1

NSMRL TECHNICAL REPORT NO. 1223 13 June 2002

RECREATIONAL DIVER RESPONSES TO 600–2500 Hz

WATERBORNE SOUND

By

D. M. Fothergill

D. Schwaller,

S.E. Forsythe,

E.A. Cudahy

Released by:

M. D. CURLEY, CAPT, MSC, USN

Commanding Officer

Naval Submarine Medical Research Laboratory

______________________________________________________________________________

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1. REPORT DATE (DD-MM-YYYY)

13-06-2002

2. REPORT TYPE

technical

3. DATES COVERED (From - To)

10-01-1999 to 9-30-2001

4. TITLE AND SUBTITLE

Recreational diver responses to 600-2500 Hz waterborne sound

5a. CONTRACT NUMBER

5b. GRANT NUMBER

5c. PROGRAM ELEMENT NUMBER

6. AUTHOR(S)

Fothergill, David M; Author

5d. PROJECT NUMBER

Schwaller, Derek ; Author

Forsythe, S E; Author

5e. TASK NUMBER

Cudahy, Edward A; Author 5f. WORK UNIT NUMBER

5913

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) 8. PERFORMING ORGANIZATION REPORT

 NUMBER

Naval Submarine Medical

Research Laboratory

Naval Submarine Base New

London Box 900

Groton, CT 06349-5900

NSMRL Report # 1223

9. SPONSORING / MONITORING AGENCY NAME(S) AND ADDRESS(ES) 10. SPONSOR/MONITOR’S ACRONYM(S)

Naval Submarine Medical Resea NSMRL

rch Laboratory

Naval Submarine Base New 11. SPONSOR/MONITOR’S REPORT

Groton, CT 06349-5900 NUMBER(S)

12. DISTRIBUTION / AVAILABILITY STATEMENT

A Approved for public release; distribution is unlimited.

13. SUPPLEMENTARY NOTES

14. ABSTRACT

Previous work (UHM, 27(Suppl): 18, 2000) investigated aversion to 600–2500 Hz waterborne sound (WBS) in US Navy

divers. This study extends previous work by investigating the effects of 600–2420 Hz WBS on psychophysical and reaction

time responses of recreational divers who have never previously experienced high levels of WBS. Nineteen male and two

female military recreational divers volunteered. Subjects wore full 3-mm wet suits (without hood or gloves). Sound

exposures consisted of 28-s pure tones at 600, 1000, 1750 and 2420 Hz, each presented at four sound pressure levels

(SPL) ranging from 140 to 166 dB re 1 μPa. At least a 50% duty cycle was used. Subjects performed an underwater visual

two-choice reaction time (RT) test while exposed to WBS. Following each sound exposure, divers rated loudness and body

vibration for each signal on a 10-point category-ratio scale. Exposures to 600–2420 Hz WBS at SPLs up to 166 dB

produce relatively low sensations of body vibration and result in small, but clinically insignificant, effects on a simple cognitive

task. 15. SUBJECT TERMS

Divers; underwater acoustics; low frequency sound; waterborne sound (WBS); psychophysical;

sound exposure;

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OF ABSTRACT

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OF PAGES

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Ronald Joe

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Report

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860-694-5157
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Prescribed by ANSI Std. Z39.18
2

RECREATIONAL DIVER RESPONSES TO 600–2500 Hz

WATERBORNE SOUND

D.M. Fothergill,

D. Schwaller,

S.E. Forsythe,

E.A. Cudahy

Naval Submarine Medical Research Laboratory

Report # 1223

Work Unit # 5913

Approved and Released by:

M. D. CURLEY, CAPT, MSC, USN

Commanding Officer

NAVSUBMEDRSCHLAB

Approved for public release; distribution unlimited.

fo.$. &*&^
3

TABLE OF CONTENTS

SUMMARY PAGE .............................................................................................................................................. 4

ABSTRACT ......................................................................................................................................................... 5

INTRODUCTION................................................................................................................................................ 6

OBJECTIVES.................................................................................................................................................... 11

HYPOTHESES TESTED........................................................................................................................................ 11

METHODS......................................................................................................................................................... 11

SUBJECTS ......................................................................................................................................................... 11

TESTING LOCATION .......................................................................................................................................... 12

DIVING SET-UP ................................................................................................................................................. 13

SOUND MAPPING AND ACOUSTIC SET-UP........................................................................................................... 14

Underwater Sound Exposures....................................................................................................................... 16

PRE AND POST DIVE TESTING ............................................................................................................................ 18

EXPERIMENTAL PROTOCOL ............................................................................................................................... 19

Underwater Reaction Time Task ................................................................................................................... 20

Subjective Ratings........................................................................................................................................ 21

Procedure for aborting a dive....................................................................................................................... 22

HEART RATE AND BREATHING FREQUENCY........................................................................................................ 23

RESULTS........................................................................................................................................................... 24

PRE- AND POST-DIVE TESTING ........................................................................................................................... 24

UNDERWATER REACTION TIME ......................................................................................................................... 24

SUBJECTIVE RATINGS ........................................................................................................................................ 25

Loudness...................................................................................................................................................... 25

Vibration...................................................................................................................................................... 25

HEART RATE AND BREATHING FREQUENCY ....................................................................................................... 27

DISCUSSION..................................................................................................................................................... 30

STUDY LIMITATIONS ........................................................................................................................................... 33

PROPOSED SPL LIMITS FOR EXPOSURE TO 600 –2500 HZ LFWBS IN RECREATION DIVERS ....................................... 33

CONCLUSIONS ................................................................................................................................................ 35

REFERENCES................................................................................................................................................... 35

ACKNOWLEDGEMENTS ............................................................................................................................... 39

APPENDIX A..................................................................................................................................................... 40

APPENDIX B..................................................................................................................................................... 41

APPENDIX C..................................................................................................................................................... 44

APPENDIX D..................................................................................................................................................... 50

APPENDIX E..................................................................................................................................................... 52

APPENDIX F ..................................................................................................................................................... 52

APPENDIX G..................................................................................................................................................... 53
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SUMMARY PAGE

The Problem

Increasing use of high-powered sonar for detection of submarines has put the recreational

diver at an increased risk of sound injury. In particular the development of new sonar systems for

use in littoral waters raises the possibility that high levels of underwater sound may encroach on

popular recreational dive sites. Currently, there is no guidance to indicate acceptable sound

exposure levels for sonar systems that operate in the 500— 2500 Hz frequency region.

Method

Nineteen male and two female recreational divers volunteered. Diving was conducted in a

large fresh water pond (Dodge Pond, Niantic, CT). Subjects wore full 3-mm wet suits (without

hood or gloves) and breathed surface supplied compressed air via a SCUBA regulator. Sound

exposures consisted of 28-s pure tones at 600, 1000, 1750 and 2420 Hz, each presented at four

sound pressure levels (SPL) ranging from 140 to 166 dB re 1 μPa1. At least a 50% duty cycle

was used. Subjects performed an underwater visual two-choice reaction time (RT) test while

exposed to waterborne sound. Following each sound exposure, divers rated loudness and body

vibration for each signal on a 10-point category-ratio scale. If the divers could not tolerate the

waterborne sound, they were instructed to follow specific abort procedures.

The Findings

There were no aborts or indications of panic resulting from the sound exposures.

Furthermore, the subjects were able to continue with a simple two-choice underwater RT test

with only minor decrements in the speed or accuracy of responding, even during the highest

intensity sound exposure. Although sound exposures above 154 dB SPL resulted in high ratings

of loudness and reports of vibration, physiological measures of heart rate (HR) and breathing

frequency remained unaffected by the underwater sound exposures. This latter finding suggests

that under the current experimental conditions the subjects did not exhibit a significant startle

response to the underwater sound exposures.

The Application

The ultimate goal of this research is to provide input for setting guidelines for peacetime

use of military active sonar that operate within the 500— 2500 Hz frequency band. Based upon

the loudness ratings it is recommended that the maximal acceptable SPL to 600–2500 Hz

LFWBS for recreational divers be no higher than 154 dB re 1 μPa. This guideline will help

ensure that operational use of low frequency sonar systems will cause no significant impact on

the recreational diver.

ADMINISTRATIVE INFORMATION

This investigation was conducted under work unit # 5913 entitled: “Recreational diver responses to 600-2500 Hz

waterborne sound.” The views expressed in this report are those of the authors and do not reflect the official policy

or position of the Department of the Navy, Department of Defense, or the U.S. Government. This report was

approved for publication on 13 June 2002 and has been designated as NavSubMedRschLab Report # 1223.

 

1

 Throughout this document, underwater sound pressure levels are given in decibels (dB) referenced to 1 μPa.
5

ABSTRACT

BACKGROUND: Previous work (UHM, 27(Suppl): 18, 2000) investigated aversion to 600–

2500 Hz waterborne sound (WBS) in US Navy divers. This study extends previous work by

investigating the effects of 600–2420 Hz WBS on psychophysical and reaction time responses of

recreational divers who have never previously experienced high levels of WBS.

METHODS: Nineteen male and two female military recreational divers volunteered. Diving was

conducted in a large fresh water pond (Dodge Pond, Niantic, CT). Subjects wore full 3-mm wet

suits (without hood or gloves) and breathed surface supplied compressed air via a SCUBA

regulator. Sound exposures consisted of 28-s pure tones at 600, 1000, 1750 and 2420 Hz, each

presented at four sound pressure levels (SPL) ranging from 140 to 166 dB re 1 μPa. At least a

50% duty cycle was used. Subjects performed an underwater visual two-choice reaction time

(RT) test while exposed to WBS. Following each sound exposure, divers rated loudness and

body vibration for each signal on a 10-point category-ratio scale. If the divers could not tolerate

the WBS, they were instructed to follow specific abort procedures.

RESULTS: No diver aborted a dive because of the sound exposure. RT was 3% slower during

the sound presentations when compared with control trials (silence) (p<0.05). Neither frequency

nor SPL significantly influenced the decrement in RT (p>0.05). The highest mean rating for

body vibration was “Very Slight”; this occurred at 600 Hz. Loudness ratings increased linearly

as SPL increased (p<0.0001) approaching a mean rating of ‘Severe” at 166 dB. The 2420 Hz

signal was perceived as significantly louder than the other frequencies (p<0.01).

CONCLUSIONS: Exposures to 600–2420 Hz WBS at SPLs up to 166 dB produce relatively

low sensations of body vibration and result in small, but clinically insignificant, effects on a

simple cognitive task. While recreational divers tolerate these sound exposures well, an

increasing number of subjects give high loudness ratings (“>Very Severe”) once the SPL

exceeds 154 dB.
6

INTRODUCTION

Most of the early research on the biophysical and psychological effects of low frequency

waterborne sound (LFWBS) in humans has focused on frequencies below 500 Hz. The impetus

for previous LFWBS studies was provided by the emergence of low-frequency active acoustics

as a critical antisubmarine warfare technology (Tyler 1992). Specifically, the U.S. Navy was

required to provide an environmental impact statement for the operational use of a newly

developed towed sonar array system (SURTASS LFA) that operates at frequencies below 500

Hz. Due to the high powered nature of this system, and the long propagation distance of low

frequency sound, there was a possibility that high levels of underwater sound may encroach on

popular recreational dive sites.

At the time when the SURTASS LFA system became operational there was little

information available in the scientific literature on the bioeffects of low frequency sound on

divers. To determine safe exposure levels to low frequency underwater sound, human diving

experiments were carried out in the 1990s by US Navy labs and a consortium of US universities

as well as the Ministry of Defence in the United Kingdom. Table 1 summarizes the studies of

low frequency underwater sound that have been conducted to date and is an update of the Table

provided in Steevens et al., (1997). Many of the studies in Table 1 were conducted to provide

data for the SURTASS LFA environmental impact statement which has been recently published

by the Department of the United States Navy (2001). The SURTASS LFA environmental impact

statement provides guidelines for peacetime use of military low frequency active sonar that

operate within the 100-500 Hz frequency band.

Recent developments in sonar technology are exploring the use of new Low Frequency

Active sonar systems that operate within the 500–2500 Hz frequency range. The higher

frequency range of the new sonar offers advantages for detecting submarines in littoral waters. In

anticipation of the operational use of these new sonar systems, the US Navy has continued to

support research investigating the bioeffects of LFWBS on divers. This continuing research

effort aims to provide information on which to formulate exposure limits for both military and

civilian divers exposed to LFA sonar within the 500 – 2500 Hz frequency range.

The current report describes the third in a series of three experiments designed to

evaluate the psychophysical effects of (LFWBS) in the 500-2500 Hz range on both US Navy

and recreational divers. During the first two experiments, 31 U.S. Navy divers were exposed to

LFWBS at 6 frequencies from 600 to 2500 Hz at Sound Pressure Levels (SPLs) up to 163 dB

re. 1 μPa. The duration of the LFWBS was from 7 to 28 seconds. The primary objective of the

first two experiments was to determine the relationship between aversion and sound pressure

level (SPL) in U.S. Navy divers exposed to sonar exposures across the frequency range of

interest. Other objectives included determining the influence of frequency, signal type, and inert

gas narcosis on aversion to LFWBS and on the presence or absence of vibration sensations.

Preliminary results have been reported in Fothergill et al., (2000, 2001a) and are included in

Table 1.

The main findings from Fothergill et al., (2000) were that aversion to LFWBS and the

probability of detecting vibration increased linearly with increasing SPL. The probability of
7

detecting vibration was greatest at 600 Hz and the least at 2000 Hz. These frequencies also

corresponded to most and least aversive frequencies, respectively. Across all frequency and signal

conditions there was a 10% probability that an aversion rating would exceed "Very Severe" (seven

on the category-ratio scale) at the highest SPL (163 dB). There was no significant difference in

aversion among the three different signal types tested in this study.

The main conclusions from Fothergill et al., (2001a) were that at SPLs of 151 dB and

above, aversion and perception of vibration to LFWBS is reduced under mild inert gas narcosis. In

contrast to previous results at lower frequencies and intensities (Sims et al., 1999), increasing the

signal duration of 600 Hz LFWBS from 7 to 28 s increased the level of diver aversion to

underwater sound, slightly, but significantly.

It should be noted that in the studies by Fothergill et al. (2000, 2001a), several of the

subjects were familiar with the effects of LFWBS, following their participation in similar

previous experiments. Furthermore, the procedures used in Fothergill et al., (2000) used a

sequential increase in SPL for a given frequency and signal type rather than random presentation.

The subjects were also under full control of the sound exposures. These procedures were

adopted to minimize the possibility of a subject de-volunteering as a result of aversion to the

sound exposures. It was thought that these precautions would optimize the chances of obtaining

usable data while at the same time enabling the main objective of the study to be met within the

limited time and budget constraints.

Because of the extensive training and experience of the US Navy divers, as well as the

conservative procedures described above, none of the divers aborted their dive or showed a panic

reaction as a result of the sound exposures. Furthermore, there were no measurable deficits in

cognitive performance or changes in hearing acuity due to the sound exposures. While the data

from Fothergill et al., (2000, 2001a) provides useful information on the psychophysical

responses of well-trained U.S. Navy divers to LFWBS, information is still needed on the

responses of other less well-trained diver populations.

The aim of this research was therefore to resolve the major concerns associated with the

response of the recreational diver, who by level of training, experience and fitness may be less

prepared to successfully cope with an unexpected exposure to LFWBS. The primary focus of the

present study was to determine the psychophysiological reactions of recreational divers

presented with sound unexpectedly and to determine if such reactions place naive divers at risk

of harming themselves. To achieve this goal, we used individuals who were not US Navy dive

trained and had never been involved in an underwater sound experiment.
Table 1

Previous Studies on the Bioeffects of Low Frequency Underwater Sound

Author Method Frequencies SPL Time of Exposure

Nyborg 1993 Modeling < 1000 Hz < 160 dB Minutes

Crum and Mao 1993 Modeling < 1000 Hz < 190 dB Minutes

Suki et al. 1994 Modeling 250 Hz Not specified Minutes

Duykers and Percy

1978

Pig exp. (head out)

(n = 4)

40-70 Hz 144-167.5 dB 1.5-18 minutes

 Rogers et al. 1994 Human exp.

(n = 5)

50-500 Hz 130 dB 4-6 sec. x 30

 Verrillo et al. 1994 Human exp.

(n = 6) +

Modeling

250 Hz < 180 dB Minutes
Table 1 Con't

Author Method Frequencies SPL Time of Exposure

Smith et al. 1996 Human exp.

(n = 27)

125, 250,

500,

1000 Hz

 (+ 5% warble)

161 dB

171 dB

181 dB

4 minutes

4-15 minutes

4-15 minutes

Steevens et al. 1994a Human exp.

Head out

(n=22)

225-275 Hz

(warble)

160 dB 5-10 min>(cont.) +

30-60 sec. x 5

Knee 

Steevens et al. 1994b Human exp.

33 fsw

(n = 18)

160-320 Hz

(warble)

160 dB 5 minutes

Steevens et al. 1999 Human exp.

60 fsw

(n = 1)

160-320 Hz

(warble)

160 dB 15 minutes

Russell and Knafelc

1995

Human exp.

33-133 fsw

(n = 22)

160-320 Hz

(warble)

160-260 Hz

(sweep)

240-320 Hz

(sweep)

160 dB 100 sec. pulses x 9

(50% duty cycle)
Table 1 Con't

Author Method Frequencies SPL Time of Exposure

Steevens et al. 1994b Human exp.

30 & 60 fsw

(n = 6)

160-320 Hz

(warble)

240-320 Hz

(sweep)

160 dB 100 sec. pulses x 9

(50% duty cycle)

Sims et al., 1999 Human exp.

Depth 1 m

(n=20)

100-500 Hz

(pure tone)

120 dB 1 sec.

 Fothergill et al.,

2001b

Human exp.

Depth 1 m

(n=23)

100-500 Hz

(pure tone, 30 Hz sweep

up and down)

130-157 dB Repeated 7 sec.

signals

Sims et al., 1998b Human exp.

Depth 1 m

(n=26)

100 Hz

(pure tone, 30 Hz sweep

up and down about center

frequency )

136 dB 7, 14, 21, 28 sec.

(50% duty cycle)

Sims and Fothergill

1999

Human exp.

Depth 1 m

(n=24)

100, 250, 500 Hz pure

tone

126 –157 dB Repeated 28 sec

signals

Parvin et al., 1994 Human exp.

20 meters depth

(n = 4)

15-1500 Hz 160 dB 5 min. sweeps x 3

Fothergill et al., 2000 Human exp.

Depth 1 m

(n=31)

600, 800, 1000, 1500

2000, 2500 Hz pure tones

and 10% hyperbolic

sweeps up and down

140 –163 dB Repeated 7 sec

signals

Fothergill et al.,

2001a

Human exp.

Depth 1 m

(n=31)

600, Hz pure tones 140, 151 and 163

dB

7, 14, 21, 28 sec

signals

(50% duty cycle)
11

OBJECTIVES

i. Determine if LFWBS presentations at frequencies between 600 and 2500 Hz at SPLs up to 166

dB result in avoidance behavioral responses (i.e. ascents to the surface to avoid the sound) and/or

a significant startle response to the sound. These data will be used to determine the potential for

causing indirect harm to a diver unexpectedly caught in a sound field. The data will predictions

of panic in divers to be made.

ii. Determine if LFWBS presentations at frequencies between 600 and 2500 Hz result in

cognitive diversion in recreational divers. Although some subjects may not show avoidance

behavior to LFWBS, there may be some degree of diversion from a task because of the sound

exposure that may interfere with diving procedures, underwater work or overall dive safety.

iii. Determine if the magnitude of a startle response to LFWBS is related to the individuals state

or trait anxiety level.

iv. Determine psychophysical perceptions of loudness and vibration to LFWBS as a function of

SPL and frequency.

Hypotheses Tested

i. Divers with the highest state and trait anxiety will be those most likely to show avoidance

behavioral responses in response to high levels of LFWBS.

ii. LFWBS will divert a diver’s attention and reduce their performance (increase reaction time

(RT)) on a two choice RT test. The increase in RT will be independent of the sound pressure

level and frequency of the sonar stimulus.

iii. LFWBS stimuli of 154 dB and above will result in a physiological startle response (i.e., a

temporary cardiac acceleration). The rationale for this hypothesis is based upon preliminary

results from NSMRL protocol 30358 that indicate the emergence of a temporary cardiac

acceleration during sound presentation at 151 dB that was more clearly defined at 163 dB.

iv. Vibration ratings will be highest for the lowest frequencies tested, and will increase in direct

proportion to the sound pressure level.

METHODS

Subjects

Active duty military and Coast Guard personnel were recruited as subjects by advertising

in the Naval Submarine Base New London paper (The Dolphin) and in local dive shops and dive

clubs. Flyers requesting subjects for the study were also placed around the Submarine Base, New

London and at the Coast Guard academy in New London. An electronic message was also sent to

various commands on the Submarine Base, New London, Coast Guard Academy and other local

Coast Guard Commands for inclusion in their plan of the day (see Appendix A).
12

Subjects were required to be at least 18 years of age and hold a recognized civilian diving

certification. (e.g. Professional Association of Diving Instructors [PADI]; National Association

of Underwater Instructors [NAUI]; Young Men’s Christian Association [YMCA] etc.). Medical

fitness for diving was screened by history (review of the Coast Guard or military medical record

and the Medical Data Form shown in Appendix B) and physical examination by a U.S. Navy

diving medical officer. Any subject with an absolute contraindication for diving as outlined by

the Recreational SCUBA Training Council’s (RSTC) guidelines for physicians (see Appendix C)

was disqualified from participating in this study for safety reasons. Qualified Navy divers as

defined in OPNAVINST 3150.27A were excluded from participating because of their extensive

dive training and the fact that the goal of this study was to evaluate the responses of recreational

divers only. To comply with the U.S. Navy diving directive OPNAVINST 3150.27A a general

waiver on physical standards for civilian-trained military divers was obtained from Naval

Military Personnel Command (CHNAVPERS) (with Bureau of Medicine and Surgery

concurrence). There were no exclusion criteria for high frequency hearing loss, which is

common in the diving community.

Nineteen male and two female active duty military recreational divers participated in the

study. The subject population had a mean age of 29 years, (range 20 - 52 years). The average

number of years diving was 5.7 years (range 0 - 16 years) with a mean number of dives since

certification of 95 (range 0 – 500).

Testing Location

All dive experiments were conducted at the Dodge Pond Acoustic Measurement Facility,

Naval Undersea Warfare Center Detachment (NUWC), Niantic, CT (see Figure 1). This site was

chosen as the testing site for the following reasons:

• The test site is secure and under U.S. Navy control (no gasoline-powered motor boats are

allowed on the pond).

• The pond’s depth, sloping sides, and mud bottom reduce the influence of sound reflections

(echoes) on the acoustic test field. When compared to a pool, the pond more accurately

simulates the open water conditions, where a diver may be exposed to LFWBS.

• NUWC’s barge facilities allow for optimal adjustment of the sound transducers and diver

placement to achieve a consistent sound field at the diver’s location.

• The pond has a very low level of background sound across all test frequencies. For most

frequencies the ambient noise levels in Dodge Pond are well below Sea State 0 (see Figure

2).

• All rigging and electronic support is protected from the weather, allowing experiments to be

conducted throughout all seasons.

• Navy diving support and local hyperbaric chambers are available. Dodge Pond is a 20-minute

drive from the Naval Submarine Medical Research Laboratory (NSMRL) hyperbaric

chambers, the Naval Ambulatory Care Center Groton and several civilian hospitals.

• The site was available for use during the time frame proposed for the current study.
13

Figure 1. The Naval Underwater Warfare Center Acoustic Test Facility, Dodge Pond, Niantic,

CT.

Diving Set-up

All dives were performed within a large, five-sided, open-top, plastic, hard-walled tank

(1.25m wide x 2.25m long x 3.5m deep), suspended beneath the command control platform of

the barge at Dodge Pond (see Figure 3). The tank is acoustically transparent at the frequencies

tested. Heated water was supplied to the tank to maintain the water temperature at a comfortable

level for the diver during the dives. All divers wore a fully deflated buoyancy compensator, a

standardized SCUBA face mask and a full 3-mm neoprene wet suit (without hoods or gloves).

Divers were negatively buoyant and suspended in the tank in a prone position at 1-m depth using

support lines to the legs and upper body. Compressed air was supplied to the divers via a

standard SCUBA regulator (US Divers) attached via a long second stage hose to SCUBA

cylinders at the surface (i.e. a hooka rig).

All dives were performed in accordance with the U.S. Navy Diving Manual Revision 4,

1999. Each subject had a tender/safety monitor at the surface that tended a safety line attached to

a diver worn harness. The tender’s role was to assist the diver in case of emergency. In addition
14

Figure 2. Ambient subsurface noise levels in Dodge Pond. SS = Sea State.

to the tender, a safety diver was also present. Communication from topside to the diver was

facilitated by an in-water communication diver recall system. Divers communicated with

topside using an underwater control console (see below) and line-pull signals.

Sound Mapping and Acoustic Set-up

Two sound sources were used to cover the frequency range for the current experiment.

An HX-188 sound projector was used for frequencies up to and including 1750 Hz and a TR-317

sound projector was used for frequencies above 1750 Hz. Both sound projectors were placed at

a depth of 0.8 m outside of the Lexan box and in line with the head and torso of the diver. The

source placement was designed to make the sound field at the diver axis in the region of head

and thorax as uniform as possible. A diagram of the transducer set up is shown in Figure 4. Prior

to human testing, the sound field in the region of the diver was mapped with the diver absent

using an array of 5 hydrophones spaced along an axis at 0.25 m intervals. The hydrophone array

was oriented along the head to foot axis of the diver position and subsequently moved to 5

positions perpendicular to its length to measure the uniformity of the sound field in a volume

around the diver. The 5 positions of the array are shown in Figure 4 and are listed below.

100

AMBIENT NOISE LEVELS OF DODGE POND

COMPARED TO DEFINED SEA STATE NOISE

100

FREQUENCY (Hz)

DATE: 5/7/96 TIME: 4PM

WEATHER: SUNNY

WATER: CALM

1000 10000
15

Figure 3: (Left)

The plastic

acoustically

transparent box

placed within the

well of the barge at

Dodge Pond. All

diving was

performed at 1 m

depth within this

box. The

underwater sound

transducers were

placed outside the

box at a depth of

0.8 m (see Figure 4

below).

Figure 4. Underwater transducer set-up and sound mapping of the diver’s volume (test space).

Sound Sources:

TR-317(2420Hz) Water level

HX-188 (600 -175011z)

Sound Mapping: 1.00m

C T T 1 1

l.OOm//

| 0.30 m

0.80 m

5 Hydrophones

0.25 m apart

5 locations alon<* the lono ^

yjr

/ TR-3I" HX-188

axis of the divers volume *

*<^

40 m

/

1.29m

Divers volumc

274 m
16

Positions used for the hydrophone array during sound mapping of the diver’s volume.

1. Center (along the diver axis at a depth of 1 m).

2. Down (0.15 m down from the diver axis).

3. Up (0.15 m up from the diver axis).

4. Away (0.20 m away from the source at the depth of the diver).

5. Toward (0.20 m toward the source at the depth of the diver).

The initial pure tone test frequencies chosen for the study were 600, 1000, 1750 and 2500

Hz. However, after preliminary sound mapping measurements were made it was found that large

deviations in the sound field occurred for the 2500 Hz tone. A more uniform sound field was

obtained when the frequency was lowered to 2420 Hz. Consequently, it was decided to change

the highest frequency tested from 2500 Hz to 2420 Hz. Results of the sound mapping for 600 Hz

through 2420 Hz are shown in Appendix D.

A schematic of the equipment set-up, used during the experiments, is shown in Figure 5.

Sound generation, acoustic monitoring and data acquisition were controlled by two IBM clone

computers. A master computer contained the primary program, written in Lab View, that

controlled the RT task and presented, stored and collected the diver’s responses transmitted from

the diver response box. The master computer also controlled a second slave computer which

provided signals to the two underwater sound projectors via their respective filters and amplifiers

to generate the underwater pure tones.

Underwater Sound Exposures

All LFWBS stimuli were 28-second pure tone signals with a rise and fall time of 20 ms.

The frequencies and Sound Pressure Levels (SPLs) of the signals are shown in Table 2. At each

of the four test frequencies, 4 SPLs between 140 and 166 dB were presented. Each subject

therefore received 16 distinct LFWBS exposures (4 SPLs x 4 frequencies); each of which was

presented twice for a total cumulative sound exposure of 14.9 min (i.e. 28-second pulse duration

x 4 frequencies x 4 SPLs x 2 presentations). The SPL for the 600 Hz was limited to 163 dB, due

to initial concern over possible vibratory effects at this frequency with higher SPLs.

The order of stimulus presentation was predetermined using a computer which randomly

ordered the 16 LFWBS stimuli together with three silence periods. The randomly generated

stimulus order matrix is shown in Appendix E and was programmed into the software that

provided the sound presentations during the experiments. The silence periods were used as

control (or sham) trials, in which the subjects performed the RT test without the presence of

LFWBS. A second computer-generated list randomly selected where, within the stimulus order

matrix, a given subject began their sound exposures (i.e., which sound exposure was first). The

conditions for the second list were that, (i) the subject would not start with a sham trial and (ii) at

least 1 subject would be represented in each one of the starting positions. Once the starting

position (initial sound exposure) had been chosen and entered into the computer, there was a

choice to go forward or backward through the stimulus order matrix. During the experiments, the

direction in which the subjects conducted the stimulus order was counter balanced. Since each

subject ran through the stimulus order matrix twice during the dive, there were six sham

exposures for comparison with the LFWBS sound exposures.
17

McIntosh

MC2500 Power

Amplifier

McIntosh

MC2500 Power

Amplifier

Wavetek

Brickwall

 Filter

Rockland

dual hi/lo

Filter

 Topside

Interface Unit

 Slave

Computer

 Master

Computer

 Custom Made

 Hydrophones

 Diver

 Response

 Box

LCD

Water Level

head

body

source

Oil

filled

cable

HX-188

Underwater Sound Projectors

TR-317

Figure 5. Schematic of the equipment set-up.
18

Table 2. SPLs tested at each frequency

Each Frequency SPL combination was tested twice per subject

Frequency

600 Hz 140 dB 148 dB 154 dB 163 dB

1000 Hz 140 dB 148 dB 154 dB 166 dB

1750 Hz 140 dB 148 dB 154 dB 166 dB

2420 Hz 140 dB 148 dB 154 dB 166 dB

Pre- and Post-Dive Testing

On the morning of the dive, a standard in-air audiogram was measured for each

subject at the NSMRL. The audiogram was conducted within a sound-proof booth

(Controlled Acoustical Environments, Industrial Acoustics Comp. Inc., NY) by a qualified

auditory technician or audiologist using a calibrated GSI 16 Audiometer (Model 1716,

Grason Stadler, MA). Subjects repeated the audiogram on the morning following their dive,

to determine if there was any change in their hearing due to the underwater sound exposures.

Statistical analysis of the data was conducted using a repeated measures analysis of variance

(ANOVA) with test day (pre versus post dive audiogram), frequency (6 levels from 500 Hz

to 6000 Hz), and ear (left or right) as independent variables. Significance was set at the 0.05

level.

After arriving at the dive site, subjects completed the State-Trait Anxiety Inventory

(STAI) for Adults (Spielberger 1983). Data from this test was used to assess the subject’s pre

dive anxiety level and to assess if our subject population’s Trait anxiety level varied substantially

from the general military population. Subjects then performed the automated

Neuropsychological Assessment Metrics (ANAM 2000) test battery to assess their cognitive and

memory function (Reeves et al., 1998).

The ANAM 2000 test battery is a computer based clinical subset of the Office of Military

Performance Assessment Technologies, Testers work bench that was derived using components

from the United Tri-service Cognitive Assessment Battery (Englund et al., 1987) and the Walter

Reed Performance Assessment Battery. The ANAM 2000 is purported to measure mental

efficiency as well as accuracy for a variety of cognitive tasks. Details of the sub-tests and their

purported measures are discussed in detail in Reeves et al., (1998). The nine sub-tests chosen for

the current experiment are listed in their order of presentation below.

Sub-tests used in the ANAM 2000 test battery

1. Demographics form

2. Stanford Sleepiness Scale – Measures alertness level

3. Simple Reaction time – Measures basic psychomotor speed

4. Code Substitution (Letter/Symbol Comparison) – Measures visual scanning and learning

5. and 9 Code Substitution (Short and Long-Delay) – Measures immediate and delayed recall

6. Matching to Sample – Measures pattern recognition, visual scanning, attention, working/short

term memory and decision making

7. Running Memory Continuous Performance Task (CPT) – Measures working memory
19

8. Mathematical Processing Task – Measures computational speed and working memory.

Each subject was guided through the computer instructions for each task to ensure they

understood how to perform the sub-task correctly. After showing satisfactory performance on

each of the tasks, they then completed the full test battery a total of three times, to assist in

stabalizing performance. A fourth test battery was conducted by each subject within 30 minutes

of completing his or her dive. Data from the third trial was compared with post dive performance

to determine if there had been a change in cognitive function because of the subject’s

participation in the study.

Performance on sub-tasks 3 through 8 was characterized by the mean reaction time

(MRT), percent accuracy of response (ACC), and throughput (TTP, the number of correct

responses per minute). Preliminary analysis of these data was conducted using paired t-tests to

assess differences in scores between pre and post dive. Because of the large number of

comparisons performed, the significance level of the paired t-test was set at 0.01 level, to reduce

the chances of committing a Type I error. In addition, a more powerful split plot repeated

measures analysis was performed on the MRT data for sub-tasks 3 through 8, to determine if

participation in the diving experiments resulted in a significant general effect on RT.

Experimental Protocol

As the primary goal of the study was to understand how a diver reacts to a sound that

he/she is not expecting, it was important that the subject remain blinded from the true objective

of the experiment until after the exposures. If the subject were to be informed that the objective

of the experiment was to investigate startle responses to LFWBS, they may form a cognitive

preparatory strategy that would reduce the chance of observing a true startle response. In an

attempt to minimize this preparatory strategy, subjects were instructed that the primary objective

of the study was to determine how well they could perform a RT task underwater, during the

presence of underwater sound. Although subjects were informed of the risks associated with

LFWBS and that LFWBS may or may not be present during the RT task, they were not

forewarned when the stimulus would be presented.

The Committee for Protection of Human Subjects at the Naval Submarine Medical

Research Laboratory, Groton, Connecticut and Naval Health Research Center, San Diego, CA

approved the study. Final approval was obtained from the Bureau of Medicine and Surgery,

Washington, D.C. After being briefed on the study, all subjects signed informed consent forms.

In addition, all female subjects underwent a pregnancy test on the morning before their dive to

ensure that they were not pregnant immediately prior to their participation in the study.

Following completion of pre-dive testing (see above), subjects were instrumented with a

three-lead electrocardiogram designed for underwater use. They then donned a 3-mm neoprene

wet suit and were trained topside on how to operate the underwater diver response console

shown in Figure 6. Topside training included: (i) practice on the underwater RT task (see below),

(ii) instructions for rating loudness and vibration, and (iii) procedures for aborting a dive.
20

Underwater Reaction Time Task

The underwater RT task was a simple two-choice visual RT task that was performed

using the underwater console shown in Figure 6. At the start of the test, the ready light on the

underwater console illuminated to warn the subject that the RT test was about to begin. Several

seconds later light #1 or light #2 was illuminated on the underwater console for 500 ms. The

subject was instructed to respond to the light stimulus by pressing either button #1 or #2 as

quickly as possible. When light #1 was illuminated, the subject responded by pushing button #2.

When light #2 was illuminated, button #1 was pressed. A timer measured the subject’s RT from

the onset of the light stimulus to when either button #1 or #2 was pushed. Measures of both

speed (RT) and accuracy were recorded for repeated stimulus presentations. Reaction times

faster than 200 ms or slower than 2 s were recorded as errors. The time interval from when the

subject responded to when the next stimulus was presented varied randomly between 1 and 3 s.

During the topside practice session, the subject performed 65 trials. Once the diver was in

place (suspended at 1 m in a prone position) and ready to begin the study, they performed an

additional 65 trials, before being exposed to LFWBS. Within 10 – 15 seconds of completing the

in-water baseline, subjects recommenced the RT task. At a random time between the 4th and the

8

th RT trial, the diver was exposed to LFWBS. The subject attempted to maintain his/her

attention on the RT time task for a further 9 RT trials while being exposed to the LFWBS. After

completing these 9 RT trials they were cued by light #3 to use the Borg scale to rate their

loudness perception and sensation of vibration during the sound exposure (Borg 1982). Each

Figure 6. The underwater diver

response box and liquid crystal display

(LCD) used during the experiments.

Divers were instructed via the back lit

LCD when the reaction time (RT) test

was about to commence and when to

rate loudness and vibration (see text for

further details). The RT and

psychophysical data were relayed to

the surface via an oil filled cable to a

purpose built top side interface unit,

before being passed to a computer for

storage and analysis (see Figure 5).

LOUDNESS VIBRATION

READY ?

BUTTON #1 BUTTON #2

ASCEND

RATING
21

LFWBS exposure lasted 28 seconds and was followed by a rest interval (silence period) of no

less than 28 s. After the rest interval subjects were instructed to begin the RT task again, and the

above procedures were repeated until all the sound presentations were completed.

For each subject and for each SPL-frequency combination, a mean RT was calculated

from the trials immediately prior to the onset of the LFWBS and a second mean RT from the

trials during the LFWBS exposure. As subjects occasionally missed the first pre-sound RT trial,

this trial was omitted from the calculation of the pre-sound RT mean. The percent change in RT

was then calculated from the difference between the pre-sound exposure and exposure RTs. This

percent change in RT was subjected to a two-way repeated measures analysis with frequency (4

levels) and SPL (4 levels) as independent variables. For the purpose of this analysis, the highest

SPL level at each frequency was considered equivalent.

A mean percent change in RT was also calculated from the six sham trials in similar

fashion to that described above. In this case, the computer picked a random time between the 4th

and the 8th RT at which to begin the sham period. RT times collected prior to this point were

considered pre–sham trials and those after this point were during the sham trial. A separate

paired t-test was conducted to compare the percent change in RT during the sham trials with the

average change in RT recorded during the LFWBS exposures. The number of choice errors

(pressing the wrong button) was also recorded for the first exposure at each sound pressure level

(i.e. sham, 140, 148 ,154 and 163 or 166 dB). Changes in the frequency of choice errors between

the sham trail and the LFWBS exposures were analyzed using the Chi-square test. Significance

for all tests were set at alpha = 0.05.

Subjective Ratings

Subjective perceptions of loudness and vibration to LFWBS were rated using the

Borg Category-ratio scale (Borg 1982) shown below. The descriptors were placed directly in

front of the diver on a waterproof placard.

Rating Descriptor

0 None at All

0.5 Extremely Slight (just noticeable)

1 Very Slight

2 Slight

3 Moderate

4 Somewhat Severe

5 Severe

6

7 Very Severe

8

9

10 Extremely Severe (almost max.)

* Maximal

The diver used the dial on the underwater console to rate the perceived loudness of the

sound and level of vibration felt. A rating of “0” indicated that no sound was heard or no
22

vibration was felt. A rating of “10” was defined as that stimulus intensity which results in the

subject wanting to immediately terminate an open ocean dive because of the loudness or

level of vibration during the sound exposure. The * or Maximal rating allows the scale to

remain open ended so that the subject could rate an exposure higher than a 10 if a 10 had

already been rated for a previous stimulus. If a diver gave a maximal response they were

asked to rate the sound presentation with a number greater than 10. They were then asked if

they wanted to continue with the experiment. All ratings given by the subject were

automatically recorded in a computer data file once the subjects pressed the “Enter” button

on the underwater console.

Statistical analyses of the loudness and vibration ratings were conducted using three-way

repeated measures analysis of variance with first versus second presentation, frequency, and

SPL as the independent variables. As the highest SPL was different for the different

frequencies, two separate analyses were performed. The first repeated measures ANOVA

analysis included all the SPLs (140, 148, 154 dB and highest SPL) and the second analysis

included only the first 3 SPLs (i.e. 140, 148 and 154 dB). Post Hoc analysis was conducted

using Tukey’s Honest Significant Difference. Significance was set for all tests at alpha =

0.05.

Procedure for aborting a dive

The diver was instructed to use the ASCEND button if they wanted to leave the sound field.

Although the divers were only 3 feet below the surface, they were instructed to pretend that they

were 15 feet below the water. If they could not tolerate the LFWBS, they were instructed that

they could ascend to the surface to avoid the sound. However, any ascent to the surface must be

done at a “safe rate”, i.e. a rate not to exceed 30 feet/min. Thus it should take the diver 30 s to

reach the surface from a pretend depth of 15 feet. To simulate a 30 s “safe” ascent, the diver was

instructed to push and hold down the ASCEND button while a timer counted down 30 seconds.

Since the duration of the sound was only 28 s and the ascent period was 30 s, a diver pressing the

ASCEND button immediately on sound presentation may remain submerged if they perform a

“safe ascent” since the sound would terminate prior to ascent. Release of the button terminated

the sound immediately at any time during the count down. Thus, divers deciding that they could

not tolerate the sound during a 30 s “safe ascent period” had to release the button to come to the

surface immediately, thereby terminating the sound exposure.

Any use of the ASCEND button terminated the RT test for that trial. Ascent to the surface to

avoid the sound was defined accordingly: 1) “Panic” - immediate ascent to the surface (failure to

push the ASCEND button), 2) “Potentially harmful ascent” -ascent faster than 30 s, 3) “Aborted

dive” - any ascent to the surface at the appropriate rate. Any use of the ASCEND button that

resulted in a “potentially harmful ascent” or “panic” eliminated further presentations for that

subject for that frequency and SPL as well as further increases in SPL for that frequency. If

subjects ascended to the surface for any reason they were asked if they desired to continue with

the dive.
23

Heart Rate and breathing frequency

Heart rate (HR) was monitored continuously during each test, using a three-lead

electrocardiogram designed for underwater use. The EKG signal was digitized at a sample

rate of 1000 Hz, using AcqKnowledge III hardware (BIOPAC Systems Inc, Santa Barbara,

CA), before being presented online on an IBM laptop and stored on hard disk for later

analysis. Beat-to-beat intervals were determined from the peak of one R wave to the peak of

the next (R-R interval) using AcqKnowledge III software. For each sound exposure or

sham trial, the R-R intervals were divided into four periods, each containing five R-R

intervals. The four time periods were: pre-sound exposure, early sound exposure (first five RR intervals during the sound exposure), late sound exposure (next five R-R intervals during

the sound exposure), and post sound exposure. The data analyzed for each subject were: the

first sham trial, the first 140 dB exposure, and the first sound exposure greater than 154 dB.

Statistical analysis was conducted using a repeated measures ANOVA, with the independent

variables being SPL (3 levels), time period (4 levels), and R-R interval (5 levels).

In addition to HR, breathing gas temperature was monitored continuously using a fast

response temperature probe (TSD102A thermister, BIOPAC Systems Inc, Santa Barbara,

CA), placed in the mouthpiece of the SCUBA regulator. The temperature probe was

interfaced to the same data acquisition system as described above. Fluctuations in gas

temperature between inhalation and exhalation allowed respiratory frequency (fb) to be

monitored throughout the dive. Output from a monitoring hydrophone was also digitized and

passed through the BIOPAC data acquisition system for synchronization of the sound stimuli

with breathing pattern and heart rate responses.

For the purpose of analysis, breathing rates (fb)were determined for approximately 28

s prior to and during the sound exposures for: (1) the first and last sound, (2) the first 140 dB

exposure, (3) the first LFWBS exposure >154 dB, and (4) the first sham exposure. A oneway repeated measures ANOVA was performed on the respiratory frequency data to

determine if there were any change in breathing rate between the sham exposures and the

highest and lowest intensity sound exposures. In addition, a separate 2-way repeated

measures ANOVA was performed on the respiratory frequencies prior to and during the first

and last sound exposure to determine if: (a) breathing rate changed over the course of the

experiment, and (b) whether fb was affected by the sound exposures.
24

RESULTS

Pre- and post-dive testing

Statistical analysis of the audiogram data showed no significant changes in hearing acuity

between the pre and post dive tests (p>0.05). The group mean ± SD State and Trait Anxiety

Scores were 28 ±5.8, and 28 ±5.6, respectively. These values fall within the 10th and 16th

percentile scores for male military recruits for State and Trait Anxiety, respectively (Spielberger,

1983). When compared with a group of qualified US Navy divers of similar age who took part in

a similar previous experiment, both State and Trait scores were significantly higher for the

recreational diver group (p<0.05).

Summary statistics showing the results of performance on the ANAM 2000

neuropsychological test battery are provided in Appendix G. Preliminary statistical analysis

showed that the only significant changes between pre- and post-testing occurred for the code

substitution, matching to sample, and math test. All the other tests showed no significant change

in RT, accuracy or throughput (all p>0.01). The code substitution test showed evidence of a

slight improvement in accuracy, from 94% to 96% post dive (p<0.01), while the math test

showed a slight improvement in RT from 2255 to 2117 ms post dive (p<0.01).

The only performance measure showing a decrement post-dive was RT on the matching

to sample test, which increased from a mean of 1174 ms to 1372 ms post dive (p<0.01). When

the RT data from all the tests on the ANAM 2000 were subjected to analysis of variance, the

overall main F statistic comparing pre versus post RT was not significant (F1,20 = 2.82, p = 0.11).

However, there was a significant interaction between pre- versus post-RT and the sub-tests on

the test battery (F6,120 = 6.25, p<0.0001). Tukey’s post hoc analysis revealed that the significant

interaction was predominantly the result of the slight increase in the mean post-dive RT on the

matching to sample test described above.

Underwater Reaction Time

During the sound exposures, RT on the underwater task was 3.34% (SD ± 4 .99%) slower

than during the period immediately prior to the onset of the sound. This was significantly

different from the RTs during the sham exposures (p<0.05), which, as expected, changed little

(mean % change = 0.36%, SD ± 7.29%) between the pre sham trials and the designated sham

trials. Although the presence of LFWBS resulted in a 3% slowing of the underwater RT,

ANOVA showed that this slowing was independent of the SPL (F3,60 = 0.97, p=0.41) and

frequency (F3,60 = 1.94, p=0.13) of the waterborne sound. Analysis of the choice errors (pressing

the wrong button) showed 3 subjects exhibiting choice errors during the first loud sound (163 or

166 dB), no subjects with choice errors during the first 140, 148 and 154 dB LFWBS exposure

and two subjects with choice errors during the first sham exposure. The total number of choice

errors was; 12 during the first loudest sound, and 2 during the sham exposure. Chi-square

analysis of these frequencies showed a significant increase in the number of choice errors during

the first loud sound compared with the first sham trial (p<0.05), but no significant difference in

error rate between the first sham trial and the first 140, 148 and 154 dB exposure (p>0.05).
25

Subjective ratings

Loudness

None of the subjects aborted the dive due to the sound exposures or pressed the abort

button on the diver response box. However, seven subjects reported that they were startled by

some of the underwater sounds. Three subjects provided loudness ratings of 9 or greater during

one or more of the sound exposures. All the high ratings were for sounds at the highest SPL and

showed no particular bias towards any one frequency (600 Hz, n=2; 1000 Hz, n= 3; 1750 Hz,

n=1; 2420 Hz, n=3). Based on these responses approximately 15% of divers would consider

immediately aborting an open ocean dive if they were exposed to 28 seconds of LFWBS at these

frequencies at SPLs between 163 and 166 dB. None of the divers gave ratings to indicate that

they would abort a dive at 154 dB or less.

Statistical analysis of the loudness ratings showed that the ratings were dependent on

frequency (F3,42 = 6.41, p<0.01) and SPL (F3,42 = 89.86, p<0.0001), but were similar for the

initial and repeat exposures (F1,14 = 0.08, p=0.79). A repeat of this analysis with the highest SPL

omitted from each frequency provided similar results. Figure 7 shows the change in loudness

ratings with SPL for each frequency. As expected, the loudness ratings increase linearly with the

increase in SPL, with differences between each loudness level being significant (p<0.001).

Tukey’s Post hoc analysis of the main effect for frequency revealed that the 2420 Hz tone was

perceived louder than all the other frequencies (all comparisons with 2420 Hz p<0.01). Since

Figure 7 does not give an indication of the wide inter-subject variability in the loudness ratings,

Figure 8 is included to show the median and 95th percentile confidence limits for the loudness

ratings at each SPL tested. This latter Figure shows that 95 percent of recreational divers would

rate the loudness of LFWBS at SPLs up to and including 154 dB as no more than Severe for

frequencies between 600 and 2420 Hz.

The correlations between the mean loudness rating and State and Trait anxiety scores

were low and non-significant (State anxiety, r = 0.16; Trait anxiety, r = 0.22).

Vibration

During the post-dive debriefing, six divers reported feeling vibration between the wet suit

and skin and a further five divers reported feeling vibration in the region of the head, ears or

sinus, during some of the sound exposures. Statistical analysis of the vibration ratings for SPLs

up to and including 154 dB showed that the sensations of vibration during the LFWBS exposures

were dependent upon SPL (F2,40 = 6.24, p<0.005), but independent of the frequency of the sound

(F3,60 = 1.38, p=0.26). However, when the highest SPL was included in the repeated measures

analysis of variance significant main effects were obtained for SPL (F3,60 = 5.68, p<0.005),

frequency (F3,60 = 3.90, p<0.05) and the SPL x frequency interaction (F9,180 = 2.27, p<0.05). The

different conclusions arising from these two analyses are best explained graphically as shown in

Figure 9. The first point to notice from Figure 9 is that the mean ratings for vibration sensation

are very low even at the highest SPL tested. Secondly, for the data points up to and including 154

dB there is little difference in the vibration ratings reported for the different frequencies or for

the different SPLs. However, when least squares linear regression lines are fitted for each

frequency using all the data points, the interaction is clearly evident from the steeper slope for

the 600 Hz frequency compared to the other frequencies.
26

SPL (dB re 1 uPa)

Loudness Rating

Nothing at all

Extremely Slight

Very Slight

Slight

Moderate

Somewhat Severe

Severe

Very Severe

0

.5

1

2

3

4

5

6

7

135 140 145 150 155 160 165 170

600 Hz

1000 Hz

1750 Hz

2420 Hz

Figure 7. Loudness ratings by frequency for the LFWBS exposures. The data are means from 21

recreational divers. The lines through the data points were fitted using least squares linear

regression. See Appendix F for the regression equations.

SPL (dB re 1 uPa)

Loudness Rating

Nothing at all

Extremely Slight

Very Slight

Slight

moderate

Somewhat Severe

Severe

Very Severe

Extremely Severe

0

0.5

1

2

3

4

5

6

7

8

9

10

139140141142143144145146147148149150151152153154155156157158159160161162163164165166

95%

5%

75%

25%

Median

Figure 8. Median and percentile loudness ratings at each SPL for the LFWBS exposures.

Data includes all frequencies and are for 21 recreational divers.
27

Variability of the vibration ratings is shown for each SPL in Figure 10. Over most of the

SPL range, there was little variability with 95% of the ratings falling below 2 (“Slight”) for SPLs

of 154 dB and below. The largest variability occurred for 600 Hz at 163 dB. However, even for

this data point 75% of the ratings given for vibration were “Very Slight” or lower. There were no

vibration ratings greater than Severe for any of the sound exposures.

Heart Rate and Breathing Frequency

All heart rate data were analyzed and presented in the beat domain. Results showing the

group mean changes in the R-R intervals for the sham exposures, and the first low (140 dB) and

high (163 – 166 dB) SPL exposures are shown in Figure 11. Statistical analyses of these data

showed that there were no significant differences in heart rate between these three conditions

(F2,40 = 0.08, p=0.92). Furthermore, heart rate was similar across the four time periods analyzed

(i.e. pre-sound exposure, early sound exposure [first five R-R intervals during the sound

exposure], late sound exposure [next five R-R intervals during the sound exposure], and postsound exposure, [F3,60 = 1.22, p=0.31]). R-R intervals within a given time period were also

similar (F4,80 = 0.69, p=0.60).

The average breathing frequency was approximately 11 breaths/min and did not differ

significantly between the beginning and the end of the dive (F1,16 = 2.85, p=0.1). The main F

statistic for the ANOVA that compared breathing rates, during the sham exposures, with

breathing rates, during the first low (140 dB) and first high SLP (163 –166 dB) exposure, was

also not significant (F2,30 = 1.73, p=0.19). This suggests that the LFWBS exposures did not

significantly impact breathing frequency. However, a separate two-way repeated measures

ANOVA performed on the respiratory frequencies prior to and during the first and last sound

exposure showed that breathing rate was increased significantly by 12.6% (1 breath/min) (F1,16 =

8.90, p <0.01) during the sound exposure. At first, these analyses seem to contradict each other.

However, they may be explained by the fact that during the majority of time over which the presound exposure respiratory frequency was calculated, the divers were not performing the

underwater RT test. In contrast, during the period when the sound was on and during the sham

period, the divers had to perform the RT task and rate loudness and vibration. Thus, the

additional cognitive and physical demands under the later condition likely resulted in the slight

increase in breathing frequency noted in the second analysis.

When breathing rate during the different LFWBS exposures was correlated with State

and Trait anxiety scores, the r-values ranged from –0.40 to 0.01. None of the correlations were

significant (p>0.05).
28

SPL (dB re 1 uPa)

Vibration Rating

Nothing at all

Extremely Slight

Very Slight

Slight

0

0.5

1

2

135 140 145 150 155 160 165 170

600 Hz

1000 Hz

1750 Hz

2420 Hz

Figure 9. Vibration ratings by frequency for the LFWBS exposures. The data are means from 21

recreational divers. The lines through the data points were fitted using least squares linear

regression. See Appendix F for the regression equations.

SPL (dB re 1 uPa)

Vibration Rating

Nothing at all

Extremely Slight

Very Slight

Slight

Moderate

Somewhat Severe

0

0.5

1

2

3

4

139140141142143144145146147148149150151152153154155156157158159160161162163164165166

95%

5%

75%

25%

Median

Figure 10. Median and percentile vibration ratings at each SPL for the LFWBS exposures. Data

includes all frequencies and are for 21 recreational divers.
29

Beat Number

R-R Interval (s)

SPL silence

0.70

0.74

0.78

0.82

0.86

0.90

-4

-3

-2

-1

0

1

2

3

4

5

6

7

8

9

10

z

a

b

c

d

SPL low (140 dB)

-4

-3

-2

-1

0

1

2

3

4

5

6

7

8

9

10

z

a

b

c

d

SPL high (163 -166 dB)

0.70

0.74

0.78

0.82

0.86

0.90

-4

-3

-2

-1

0

1

2

3

4

5

6

7

8

9

10

z

a

b

c

d

Mean+SE

Mean-SE

Mean

Figure 11. Group mean ± SE for R-R intervals recorded during the first sham (silence), low (140

dB) and high (163 – 166 dB) LFWBS exposures. Onset of the LFWBS stimulus occurs between

R-R interval “0” and “1”. While the sound was on for 28 s, only the first 10 R-R intervals during

the sound exposure (i.e. 1 through 10) were subjected to statistical analysis. The LFWBS

stimulus was switched off between the “z” and “a” R-R interval.
30

DISCUSSION

Our results indicate that the current group of recreational divers tolerated the underwater

sound exposures well. There were no aborts or indications of panic resulting from the sound

exposures. Furthermore, the subjects were able to continue the underwater RT test with only

minor decrements in the speed or accuracy of responding, even during the highest intensity

sound exposure. Although sound exposures above 154 dB SPL resulted in high ratings of

loudness and reports of vibration, physiological measures of heart rate (HR) and breathing

frequency remained unaffected by the underwater sound exposures. This latter finding suggests

that under the current experimental conditions the subjects did not exhibit a significant startle

response to the underwater sound exposures. Since we hypothesized that a startle response would

be evident at the higher SPL exposures the following discussion focuses on possible reasons for

our non-significant findings.

Previous studies, in which subjects have been unexpectedly exposed to in-air noise

bursts, have elicited either an orienting reflex (OR), a defense reflex (DR) or a startle reflex

(SR). The OR is reflected by a HR deceleration, whereas the DR and SR are characterized by

long or short latency HR acceleration, respectively (Graham 1979). The type of response elicited

is dependent upon the stimulus parameters, experimental design and instructions to subjects. In

addition, conditioning of the cardiac DR versus OR has been related to the affective content of

the stimulus (Gautier and Cook 1997; Cook et al. 1986), and there is evidence that the SR is

potentiated by aversive emotional states (Cook et al. 1992). For further details on the

physiological significance and theoretical construct of these reflexes or responses, the reader is

referred to papers by Turpin (1986) and Barry and Maltzman (1985).

In our previous underwater diving studies, underwater sound presented at frequencies

between 100 and 500 Hz at SPLs up to 157 dB provoked a temporary decrease in HR (Fothergill

et al. 1998b). This HR deceleration was attributed to a normal non-habituating voluntary OR. In

contrast to the findings of Fothergill et al. (1998b), the current study showed no evidence of a

cardiac OR or SR. We can not discount the possibility that the underwater sounds elicited a DR,

since HR measures beyond 5 beats post stimulus were not analyzed. The onset of the long

latency cardiac acceleration, typical of a DR, usually occurs after at least 2 seconds following the

sound stimulus. However, with initial exposure to a high intensity stimulus, HR may not reach a

peak until 35 s after the stimulus (Turpin 1986). As the duration of sound exposures in the

current study were much longer than the typical auditory startle stimuli used for air studies, any

long latency HR responses will likely have been affected by possible reactions to the sound

stimulus being switched off.

It is possible that the cardiac response to the sound in the previous experiment was

dependent on voluntary attentional processes and the significance of the sound stimuli to the

subjects. In the current experiments, subjects were told to ignore the sound stimulus and

continue with the RT time task. Although they were informed that the sounds might be loud, they

were not given any indication that they may be aversive. In contrast, during the experiments

conducted by Fothergill et al. (1998b), subjects were required to attend to the stimulus and were

asked to rate their level of aversion to the sound. Clearly, the instructions to the subjects in the

two experiments were different, which may have induced differences in cortical set and
31

expectations about the aversive nature of the sound. O’Gorman (1990) has suggested that

whether or not a voluntary OR is elicited is dependent upon the subject’ cortical set and the level

of activation of the left hemisphere. Only when subjects are required to think actively about the

stimulus is a common cortical set given to all subjects and consistent responding to be expected

(O’Gorman 1990).

Further evidence of the effects of cortical set on HR responses to underwater sound were

shown in the experiments conducted by Waltz and Fothergill (1999). Their findings are shown in

figure 12. When subjects were exposed to 600 Hz sound at 163 dB, a clear increase in HR was

evident by the 5th beat post stimulus when breathing air at 1 m. However, when the same

subjects breathed a normoxic 23% N2O mixture at 1 m, this short latency HR increase was no

longer evident. It is thus possible that manipulation of cortical set or attention processes, by

either inert gas narcosis or by a distracter task as in the case of the current experiment, can

reduce or abolish the cardiac responses to an underwater sound stimulus.

BEAT 

R-R Interval (s)

GAS: A

0.88

0.92

0.96

1.00

1.04

SPL (dB re 1 uPa): 140

GAS: N

0.88

0.92

0.96

1.00

1.04

0 1 2 3 4 5 6 7 99 A B C D E

SPL (dB re 1 uPa): 151

0 1 2 3 4 5 6 7 99 A B C D E

SPL (dB re 1 uPa): 163

0 1 2 3 4 5 6 7 99 A B C D E

Mean+SE

Mean-SE

Mean

Figure 12. Group mean ± SE for R-R intervals recorded during exposures to different sound

pressure levels of a 600 Hz underwater pure tone while breathing air at 1 m (Gas: A) or a

normoxic 23% N2O gas mixture (Gas: N) at the same depth. The data are for 29 US Navy Divers

who participated in the study by Waltz and Fothergill (1999). Onset of the LFWBS stimulus

occurs between beat “0” and “1”. Beats 1 through 7 are during the sound exposure. The LFWBS

stimulus was switched off between beat “99” and “a”. Beats A through E were post stimulus.

Note the difference in HR response during the sound presentations between the two different gas

conditions (see text for further details).
32

Our data shows that the underwater sound stimuli significantly increases RT, and, at the

highest SPLs, increases the number of choice errors on a two-choice RT time task. Similar

findings have also been found for in-air acoustic startle experiments (Fitzpatrick and Paige 1997;

Vlasak 1969). Fitzpatrick and Paige (1997) found that a 110 dB re 20 μPa 50-ms burst of white

noise increased RT to the first button press in a sequential memory test by 220 ms. Furthermore,

subjects with larger orbicularis oculi and sternocleidomastoid EMG amplitude responses to the

startling stimuli showed greater RT slowing. Interestingly, changes in HR evoked by the startling

stimulus were not related to RT slowing. Vlasak (1969) also noted that simple RT lengthened

following a loud burst of sound from a klaxon-hoot. The sound intensity of the klaxon-hoot was

100 dB re 20 μPa at 1-m distance with a mean frequency of 300–400 Hz and 2000–3000 Hz. In

the same set of experiments, Vlasak also noted that the number of errors on a simple math test

increased significantly during the first 15 seconds following the startle stimulus.

It thus seems that a strong sound stimulus can temporarily interrupt the train of thought of

an ongoing activity. Furthermore, if the startle stimulus is loud enough, some individuals may

make mistakes in decision making immediately following the stimulus. However, our subjects

showed only small decrements on the RT task in response to the underwater sound stimuli, that

were largely independent of the SPL and frequency. Thus, from a practical perspective, these

minor temporary effects on simple mental activity following exposure to the levels of underwater

sound used in the current experiments are of little practical concern.

The only performance measure showing a post-dive decrement was RT on the matchingto-sample test which lengthened by 17%. The reason for this performance decrement is unclear.

One possibility is that it is a Type I error or a result of an outlier. Analysis of the group data

showed that the post-dive standard deviation for RT on this subtest was almost double that of the

pre-dive standard deviation. However, the difference between the two standard deviations was

not significant. Furthermore, inspection of individual RTs did not reveal any particular

remarkable outliers in the post dive data set. Of the 21 subjects, 15 showed longer RTs, 2

subjects were within 10 ms of their pre-dive score and 4 subjects improved on the matching-tosample test post-dive. As a precaution against committing a type I error, alpha for this test was

set at 0.01 rather than 0.05. Thus, it seems likely that the slowing of RT on this test was due to

factors other than statistical error.

Recently, Lowe and Reeves (1999) used the ANAM 2000 neuropsychological test battery

to determine if cognitive function was affected during a 1000 fsw chamber saturation dive.

Results of their study showed that Matching-To-Sample was the only subtest to show a

significant performance decrement at depth. The Matching-To-Sample test was also found to be

the most sensitive test for detecting cognitive changes associated with decompression stress in a

diver who exhibited delayed decompression symptoms following accelerated decompression

from a saturation dive (Lowe et al., 1999). In the present study, all of the divers were exposed to

the LFWBS during the dive. Without additional data from divers performing the experiment

without the sound exposure, we can not confidently distinguish the cause of the decreased

performance on the matching-to-sample test between the stresses of the dive and the effects of

LFWBS. At a minimum, it would seem that one or both of these factors may have contributed to

the post-dive performance decrement on the matching-to-sample task.
33

Study Limitations

When interpreting the above findings we acknowledge some of the limitations of the

study. First, as all subjects were volunteers, it is uncertain how well our subject population

represents the responses of the general recreational diver population. The state and trait anxiety

scores indicate that our subject population was less anxious than the general population of

military recruits. It is possible that the physical and psychological aspects of diving tend to

attract low-anxiety personalities and/or dissuade highly anxious individuals from conducting or

completing their dive certification. It may also be that divers learn to inhibit state anxiety since it

tends to disrupt performance under water (Baddley 1972; Mears and Cleary 1980). In addition, it

is likely that highly anxious recreational divers would be less likely to participate in the current

study due to the potential aversive nature of the sound stimulus. There is evidence that high trait

anxiety individuals exhibit significantly larger startle responses than low trait anxiety individuals

(Filion and Brown 1997). Thus, the low anxiety scores of our diver population may be another

reason for the lack of a startle response in the current study.

A second limitation of the study is that its is ethically unacceptable to place novice divers

in a situation where they would be completely unaware that they were about to be exposed to a

potentially aversive underwater sound stimulus. Consequently, subjects were made aware that,

through the informed consent process, they would be exposed to loud sounds underwater. This

likely resulted in some a priori expectation by the subject that may have reduced the chance of

observing a startle response. Clearly, this expectation would be absent in a diver exposed to a

sonar signal while conducting a recreational dive in the open ocean. Post-dive reports from the

subjects did, however, indicate that one-third of the subjects were startled by one or more of the

underwater sound stimuli. Although the subjective reports are not reflected in our physiological

measures of startle, more sensitive physiological measures of startle (e.g. eye blink reflexes) may

have indicated that startle was present.

Other post dive comments revealed that approximately one-half of the subjects said they

would surface if they heard these sounds during a recreational dive. Interestingly, at the highest

SPLs only two subjects gave loudness ratings of 10, which indicated they would immediately

abort an open ocean dive because of the sound exposure.

Proposed SPL limits for exposure to 600 –2500 Hz LFWBS in recreation divers

Although the mean HR data showed no evidence of a cardiac startle response, many

individuals still found some of the underwater sound stimuli startling or annoying. Bjok (1999)

has shown that the annoyance resulting from a sound stimulus is not necessarily associated with

the evoked startle response. Thus,when behavioral or physiological indications of startle are not

evident, we need to rely on the subject’s subjective responses to determine acceptable exposure

levels to underwater sound. This approach was used in setting the SPL exposure limits to

LFWBS for recreational divers in the US Navy’s SURTASS LFA Environmental Impact

Statement (2001). A similar approach is adopted here to help define acceptable SPL exposure

limits to 600 – 2500 Hz LFWBS.

Using the subject’s loudness responses, figure 13 shows the change in percentage of

loudness ratings that exceed ‘Very Severe’ as a function of SPL. A rating of 7, or ‘Very Severe’
34

loudness, was chosen as the high rating cut off point, to conform with the convention used for

setting SPL exposure limits to 100 – 500 Hz LFWBS (Cudahy et al., 2002, Department of the

United States Navy 2001). Furthermore, since a loudness rating of 10 was considered the point at

which a diver would abort an open ocean dive, choosing a value less than 10 as the high rating

cut off will provide a level of conservatism when estimating the dive abort risk for a given sound

exposure. Figure 13 shows that only one subject rated the loudness of the LFWBS at 154 dB,

greater than ‘Very Severe’. However, once the SPLs exceed 154 dB there was a sharp increase in

the number of subjects providing loudness ratings greater than ‘Very Severe’. These data suggest

that if recreational divers are exposed to 600–2500 Hz LFWBS at SPLs in excess of 154 dB,

there is an increased risk that a diver will abort a dive because of the sound. It is therefore

recommended that the maximal acceptable SPL at 600 –2500 Hz LFWBS for recreational divers

be no higher than 154 dB. Based upon the data in Figure 8 it is estimated that only 5% of divers

would rate the loudness of 600–2500 Hz LFWBS greater than ‘Severe’ at an SPL of 154 dB.

Sound Pressure Level (dB re. 1 uPa)

Percentage of Loudness ratings > Very Severe

0

2

4

6

8

10

12

138 144 150 156 162 168

n = 1

n = 1

n = 4 (600 Hz only)

n = 4

(1000 - 2420 Hz)

Figure 13. Percentage of loudness ratings greater than 'Very Severe' versus SPL. The line

through data points is fitted with an exponential. (n = the number of subjects contributing to each

data point).

The proposed maximum acceptable SPL for the 600–2500 Hz frequency region is well

below the minimum SPL at which bare-headed divers have reported physiological effects (other

than sensations of vibration) from underwater sound exposures at these frequencies. In a study

conducted by Parvin et al., (2001), bareheaded divers were exposed to underwater sound up to a

maximum SPL of 191 dB re. 1μPa in the frequency range from 800–2250 Hz. In their study, the
35

minimum SPL causing termination of the sound exposures was between 176 and 185 dB. The

reasons given for termination were that the sound affected balance and resulted in dizziness

during the exposures. The effects subsided once the sound was removed. Using the subjective

comments from their divers and a 5 out of 10 loudness rating, Parvin et al., (2001) commented

that the maximum acceptable exposure level for recreational divers to underwater sound at

frequencies from 880 Hz to 2250 Hz ranged between 142 and 153 dB. It should be noted that

although Parvin et al., (2001) used a 10-point loudness scale, the descriptive anchors on the scale

were different than those used in the present study. In the current study, a rating of 5 was given if

the diver perceived the loudness of the sound to be ‘Severe.’ In contrast, 5 on the loudness scale

used by Parvin et al., (2001) indicated a sound that was “loud, but not disturbing.” Despite the

difficulties in comparing the two data sets, our proposed recreational diver SPL exposure limits

to 600–2500 Hz LFWBS are not far removed from the upper limit recommended by Parvin et al.,

(2001).

CONCLUSIONS

Waterborne sound at frequencies from 600-2420 Hz at SPLs up to 166 dB for up to 28 s

is tolerated well by bare headed SCUBA divers. Other than very slight sensations of vibration,

which are greatest at the lower end of the frequency range, there is minimal physiological impact

of these sound exposures. Furthermore, at SPLs below 166 dB there is little impact of these

LFWBS exposures on simple cognitive performance. Although none of the divers aborted the

dive because of the sound exposures, an increasing number of subjects gave high loudness

ratings (“>Very Severe”) once the SPL exceeded 154 dB. Based upon the loudness ratings it is

recommended that the maximal acceptable SPL to 600–2500 Hz LFWBS for recreational divers

be no higher than 154 dB re 1 μPa.

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ACKNOWLEDGEMENTS

Supported by the Office of Naval Research Code 341. The views expressed in this report

are those of the authors and do not reflect the official policy or position of the Department of the

Navy, the Department of Defense or the US Government. This work was conducted while Dr.

Fothergill was on assignment leave from the Research Foundation of the State University of New

York at Buffalo through an Assignment Agreement with the Naval Submarine Medical Research

Laboratory, Groton, CT. The work was done by US government employees as part of their

official duties and therefore cannot be copyrighted.

The dedicated and professional efforts of Mr. Rick Donlon, MDV (Ret), BMC(DV)

Walter Von Borstel, EM2(DV) Lloyd LeNormand and CDR Keith Wolgemuth MSC in

providing diving supporting are acknowledged and greatly appreciated. Support and training on

the ANAM 2000 neuropsychological test battery was provided by LT Michael Low MSC. In

particular, his assistance in the statistical analysis and interpretation of the ANAM 2000 data is

greatly appreciated. Our thanks are also extended to Linda Hughes and HM3 Michael McFadden

who administered the audiograms to the subjects. The tireless efforts of Dr. Steven Forsythe, and

John Armstrong at the Naval Underwater Warfare Center, RI, during modification and

development of the software for sound presentation and data collection were instrumental in

contributing to the success of this study. Finally, we especially extend our thanks to the subjects

who volunteered their time to participate in this study.
40

Appendix A:

ADVERTISEMENT PUBLISHED IN THE PLAN OF THE WEEK OF VARIOUS

COMMANDS REQUESTING DIVE VOLUNTEERS FOR THE STUDY

Active Duty SCUBA Divers needed for Navy dive study!

Recently the U.S. Navy produced an environmental impact statement on the use of the

Surveillance Towed Array (SURTASS) Low Frequency Active Sonar (LFA) System. The

SURTASS LFA sonar system uses specialized sounds and echo detection methods to detect and

track submarines. As these low frequency sonar sounds can travel long distances, some of the

sound may reach popular dive sites. Research conducted by the Naval Submarine Medical

Research Laboratory (NSMRL) provided important data that contributed to development of the

environmental impact statement. In particular, human diving studies conducted by NSMRL

researchers, with the aid of recreational diver volunteers as subjects, helped to provide guidance

for the operational use of the SURTASS LFA sonar system.

Due to recent developments in sonar technology, NSMRL scientists are currently

extending their research into a higher frequency region than that studied in the human dive

experiments for the SURTASS LFA sonar system. In the past two years NSMRL researchers

have conducted several successful experiments investigating divers’ subjective responses to

different levels of sound within the 600 to 2500 Hz frequency region. Experiments were

conducted with the help of US Navy trained divers as volunteer subjects.

The objective of these human dive experiments is to provide guidance on the acceptable

level of sound that can be used when using these sonars near potential dive sites. As this

guidance needs to apply to the general diver population, the final set of diving experiments

planned for July of this year will require civilian trained/certified divers both, male and female,

(i.e. NAUI, PADI or equivalent certification) as experimental subjects. The study is being

conducted at the NSMRL, on Submarine Base New London, CT and at Dodge Pond Niantic, CT,

between July 12th and July 27th. The purpose of the study is to see if waterborne sound in the

frequency range 600 to 2500 Hz distracts a diver’s ability to concentrate on a simple task.

Testing is noninvasive (i.e. no blood draws) and involves one day of diving and a 30 min hearing

test on the morning of the dive and the morning after the dive. Volunteers may be eligible to

receive experimental stress pay following their participation in the diving portion of this study.

If you are over 18 and are active duty military or Coast Guard, and have a civilian

diving qualification, and wish to participate in this research, please contact:

Dr. David Fothergill at 860 694 2536

Email fothergill@NSMRL.NAVY.MIL

or Rick Donlon MDV at 860 694 4907

Email donlon@NSMRL.NAVY.MIL
41

Appendix B:

MEDICAL DATA FORM

Name: ____________________________________________

SSN___________________

Sex (Circle) Male Female

1. Age (years)_______ (months)_______ DOB_____________

2. Weight (lbs.)_______

3. Height (inch)_______

4. Are you currently qualified to dive? Circle Yes No:

5. Level of certification_________________

Years of diving experience____________ Approximate date of last dive__________

Approximate number of dives conducted since certification___________

Are you a U.S. military trained diver? Circle Yes No

6. What is your NEC? __________

7. Have you ever had an episode of AGE (arterial gas embolism) or DCS (decompression

sickness)? Circle Yes No If yes, please give approximate dates and

details.________________________________________________________________________

______________________________________________________________________________

______________________________________________________________________________

______________________________________________________________________________

____________________________________________________________________________

8. Do you have any neural deficits? (patches of numb or tingling skin, motor weakness,

memory disturbance, seizures, tumor or aneurysm, stroke, spinal cord injury) Circle:Yes

No If yes, please describe.

______________________________________________________________________________

______________________________________________________________________________

______________________________________

9. Have you ever had surgery? Circle Yes No If so, describe what organ system or

body part, dates and reasons.
42

______________________________________________________________________________

______________________________________________________________________________

______________________________________________________________________________

______________________________________________________________________________

____________________________________________________________________________

10. Do you have any metal objects/hardware in your body? (i.e. screws, rods, pins or shrapnel

etc.)

Circle Yes No If yes, what and

where?____________________________________________________________

11. Smoking Status: Circle Non Smoker Occasional Smoker Smoker 1ppd 2ppd >2ppd

12. Do you have any chronic orthopedic complaints? i.e. knee pain, low back pain, chronic pain

related to injury/accident etc. Circle Yes No If yes please explain

______________________________________________________________________________

______________________________________________________________________________

______________________________________________________________________________

_________________________________________________________

13. Have you ever suffered a head injury resulting in: (Circle) concussion loss of consciousness

seizure? Please give dates and details:

______________________________________________________________________________

______________________________________________________________________________

______________________________________________________________________________

_________________________________________________________

14. Do you have any hearing difficulties or have you had ear surgery or chronic ear infections?

Circle: Yes No . If yes, please explain:

______________________________________________________________________________

______________________________________________________________________________

______________________________________________________________________________

______________________________________________________________________________

____________________________________________________________________________

15. Do you have any breathing, lung or heart problems (asthma, emphysema, punctured lung,

bronchitis, arrhythmia, congestive heart failure, heart attack, high blood pressure, fainting)? If
43

yes, please explain:

______________________________________________________________________________

______________________________________________________________________________

______________________________________________________________________________

______________________________________________________________________________

____________________________________________________________________________

16. Are you currently under medical care or taking any medications? Circle Yes No. If yes,

please list medications and indications.

______________________________________________________________________________

______________________________________________________________________________

______________________________________________________________________________

______________________________________________________________________________

____________________________________________________________________________

17. Do you have any other conditions such as sickle cell disease, polycythemia, leukemia,

claustrophobia, psychosis, panic disorder, drug or alcohol abuse? If yes please explain.

______________________________________________________________________________

______________________________________________________________________________

______________________________________

18. Are you currently pregnant? Circle: Yes No

Have you been treated for any of the above conditions or are you currently under the care of a

physician or health care provider?

______________________________________________________________________________

______________________________________________________________________________

______________________________________
44

Appendix C

GUIDELINES FOR RECREATIONAL SCUBA DIVER'S PHYSICAL EXAMINATION

Instructions to the Physician:

Recreational scuba (self-contained underwater breathing apparatus) diving has an excellent

safety record. To maintain this status it is important to screen student divers for physical

deficiencies that could place them in peril in the underwater environment.

The Recreational Scuba Diver's Physical Examination contains elements of medical

history, review of systems and physical examination. It is designed to detect conditions that put a

diver at increased risk for decompression sickness, pulmonary overinflation syndrome with

subsequent cerebral gas embolization and loss of consciousness, that could lead to drowning.

Additionally, the diver must be able to withstand some degree of cold stress, cope with the

optical effects of water and have a reserve of physical and mental abilities to deal with possible

emergencies.

The history, review of systems and physical examination should include, as a minimum,

the points listed below. The list of contraindications, relative and absolute, is not all-inclusive. It

only contains the most commonly encountered medical problems. The brief introductions should

serve to alert the physician to the nature of medical problems that put the diver at risk, and (lead

him) to consider the individual patient's state of health.

Diagnostic studies and specialty consultations should be obtained as indicated to satisfy

the physician as to the diver's status. A list of references is included to aid in clarifying issues

that arise. Physicians at the Diver Alert Network (DAN) are available for consultation by phone

(919) 684-2948 during normal business hours. For emergency calls 24 hours, 7 days a week call

(919) 684-8111.

Some conditions are absolute contraindications to scuba diving. Conditions that are

absolute contraindications place the diver at increased risk for injury or death. Others are relative

contraindications to scuba that may be resolved with time and proper medical intervention.

Ultimately the physician should decide with the individual, based on his knowledge of the

patient's medical status, whether the individual is physically qualified to participate in scuba

diving.

Remember at all times that scuba is a recreational sport, and it should be fun, not a source

of morbidity or mortality.

CARDIOVASCULAR SYSTEMS

Relative Contraindications: The diagnoses listed below potentially render the diver unable to

meet the exertional performance requirements likely to be encountered in recreational diving.

The diagnoses listed may lead the diver to experience cardiac ischemia and its consequences.

Formalized stress testing is encouraged if there is any doubt regarding physical performance

capability. The suggested minimum criteria for stress testing in such cases are 13 METS. Failure

to meet the exercise criteria is disqualifying. Conditioning and retesting may make later

qualification possible.

• History of CABG or PCTA for CAD

• History of myocardial infarction

• Hypertension
45

• History of dysrhythmias requiring medication for suppression

• Valvular regurgitation

• Asymptomatic mitral valve prolapse

• Pacemakers - The pathologic process that necessitated pacing should be addressed regarding

the fitness to dive. Finally in those instances that the problem necessitating pacing does not

preclude diving, will the diver be able to meet the performance criteria? Note: Pacemakers

must be certified by the manufacturer as able to withstand the pressure changes involved in

recreational diving (to depths of 130 feet of seawater).

Absolute Contraindications.- Various gas emboli produced during decompression may cross

intracardiac shunts and enter the cerebral circulation with potentially catastrophic results.

Asymmetric septal hypertrophy and valvular stenosis may lead to the sudden onset of

unconsciousness during exercise.

• Congestive heart failure

PULMONARY

Any process or lesion that impedes airflow from the lung places the diver at risk for pulmonary

overinflation with alveolar rupture and the possibility of cerebral air embolization. Asthma

(reactive airway disease), COPD cystic or cavitating lung diseases all may lead to air trapping.

Spirometry, provocative tests such as methacholine challenge and other studies to detect air

trapping should be carried out to establish to the examining physician's satisfaction that the diver

is not at risk. A pneumothorax that occurs or recurs while diving is catastrophic. As the diver

ascends, air trapped in the cavity expands rapidly producing a tension pneumothorax.

Relative Contraindications:

• History of prior asthma or reactive airway disease (RAD)*

• History at exercise/cold induced bronchospasm (EIB)*

• History of solid, cystic or cavitating lesion*

• Pneumothorax secondary to thoracic surgery,* trauma or pleural penetration,* previous

overinflation injury

• Restrictive disease**

(*Air trapping must be excluded) (**Exercise testing necessary)

Absolute Contraindications:

• Active RAD (asthma), EIB, COPD or history of the same with abnormal PFTs or positive

challenge

• Restrictive diseases with exercise impairment

• History of spontaneous pneumothorax

NEUROLOGICAL
46

Neurologic abnormalities that affect a diver's ability to perform exercise should be assessed

individually based on the degree of compromise involved.

Relative Contraindications:

• Migraine headaches whose symptoms or severity impair motor or cognitive function

• History of head injury with sequelae other than seizure

• Herniated nucleus pulposus

• Peripheral neuropathy

• Trigeminal neuralgia

• History of spinal cord or brain injury without residual neurologic deficit

• History of cerebral gas embolism without residual pulmonary air trapping has been excluded

• Cerebral palsy in the absence of seizure activity

Absolute Contraindications: Abnormalities where the level of consciousness is subject to

impairment put the diver at increased risk of drowning. Divers with spinal cord or brain

abnormalities where perfusion is impaired are at increased risk of spinal cord or cerebral

decompression sickness.

• History of seizures other than childhood febrile seizures

• Intracranial tumor or aneurysm

• History of TIA or CVA

• History of spinal cord injury, disease or surgery with residual sequelae

• History of Type II (serious and/or central nervous system) decompression sickness with

permanent neurologic deficits

OTOLARYNGOLOGICAL

Equalization of pressure must take place during ascent and descent between ambient water

pressure and the external auditory canal, middle ear and paranasal sinuses. Failure of this to

occur results at least in pain and in the worst case rupture of the occluded space with disabling

and possible lethal consequences.

The inner ear is fluid filled and therefore noncompressible. The flexible interfaces between the

middle and inner ear, the round and oval windows, are however subject to pressure changes.

Previously ruptured but heated round or oval window membranes are at increased risk of rupture

due to failure to equalize pressure or due to marked overpressurization during vigorous or

explosive Valsalva maneuvers.

The larynx and pharynx must be free of an obstruction to airflow. The laryngeal and epiglottic

structures must function normally to prevent aspiration.

Mandibular and maxillary function must be capable of allowing the patient to hold a scuba

mouth piece. Individuals who have had mid-face fractures may be prone to barotrauma and

rupture of the air filled cavities involved.
47

Relative Contraindications:

• Recurrent otitis externa

• Significant obstruction of external auditory canal

• History of significant cold injury to pinna

• Eustachian tube dysfunction

• Recurrent otitis media or sinusitis

• History of TM perforation

• History of tyrnpanoplasty

• History of mastoidectomy

• Significant conductive or sensorineural hearing impairment

• Facial nerve paralysis, not associated with barotrauma

• Full prosthodontic devices

• History of mid-face fracture

• Unhealed oral surgery sites

• History of head and/or neck therapeutic radiation

• History of temperomandibular joint dysfunction

Absolute Contraindications:

• Monomeric TM

• Open TM perforation

• Tube myringotomy

• History of stapedectomy

• History of ossicular chain surgery

• History of inner ear surgery

• History of round window rupture

• Facial nerve paralysis secondary to barotrauma

• Inner ear disease other than presbycusis

• Uncorrected upper airway obstruction

• Laryngectomy or status post partial laryngectomy

• Tracheostomy

• Uncorrected laryngocele

• History of vestibular decompression sickness

GASTROINTESTINAL

Relative Contraindications: As with other organ systems and disease states, a process that

debilitates the diver chronically may impair exercise performance. Additionally diving activity

may take place in areas remote from medical care. The possibility of acute recurrences of

disability or lethal symptoms must be considered.

• Peptic ulcer disease

• Inflammatory bowel disease
48

• Malabsorption states

• Functional bowel disorders

• Post gastrectomy dumping syndrome

• Paraesophageal or hiatal hernia

Absolute Contraindications: Altered anatomical relationships secondary to surgery or

malformations that lead to gas trapping may cause serious problems. Gas trapped in a hollow

viscous expands as the giver surfaces and can lead to rupture or in the case of the upper GI tract,

emesis. Emesis underwater may lead to drowning.

• High grade gastric outlet obstruction

• Chronic or recurrent small bowel obstruction

• Enterocutaneous fistulae that do not drain freely

• Esophageal diverticula

• Severe gastroesophageal reflux

• Achalasia

• Unrepaired hernias of the abdominal wall potentially containing bowel

METABOLIC AND ENDOCRINOLOGICAL

Relative Contraindications: With the exception of diabetes mellitus, states of altered hormonal or

metabolic function should be assessed according to their impact on the individual's ability to

tolerate the moderate exercise requirement and environmental stress of sport diving. Generally

divers with altered hormonal status should be in as near an optimal physiologic state as is

possible. It should be noted that obesity predisposes the individual to decompression sickness

and is an indicator of poor overall physical fitness.

• Hormonal excess or deficiency

• Obesity

• Renal insufficiency

Absolute Contraindications: The potentially rapid change in level of consciousness associated

with hypoglycemia in diabetics on insulin therapy or oral hypoglycemic medications can result

in drowning. Diving is therefore contraindicated.

PREGNANCY

Venous gas emboli formed during decompression may result in fetal malformations. Diving is

absolutely contraindicated during any stage of pregnancy.

HEMATOLOGICAL

Abnormalities resulting in altered rheological properties may increase the risk of decompression

sickness.

Relative Contraindications: Absolute Contraindications:
49

Sickle cell trait Sickle cell disease

Acute anemia Polycythemia

Leukemia

ORTHOPEDIC

Relative impairment in mobility particularly in the small boat environment or ashore with

equipment weighing up to 40 pounds must be assessed. The impact of exercise ability is also an

important consideration.

Relative Contraindications

• Chronic back pain

• Amputation

• Scoliosis - must also assess impact on pulmonary function

• Aseptic necrosis - possible risk of progression related to adequacy of decompression

BEHAVIORAL HEALTH

Behavioral: The diver's mental capacity and emotional makeup are important to safe diving. The

student diver must have sufficient learning abilities to grasp information presented to him by his

instructors, be able to safely plan and execute his own dives and react to changes about him in

the underwater environment. The student's motivation to learn scuba and his ability to deal with

potentially dangerous situations is also crucial to safe diving.

Relative Contraindications:

• Developmental delay

• History of drug or alcohol abuse

• History of previous psychotic episodes

Absolute Contraindications:

• Inappropriate motivation to dive - solely to please spouse or partner, to prove oneself in the

face of personal fears

• Claustrophobia and agoraphobia

• Active psychosis or while receiving psychotropic medications

• History of panic disorder

• Drug or alcohol abuse
50

Appendix D

RESULTS OF THE SOUND MAPPING

The tables below summarize the deviations from the median sound pressure at each of the

four test frequencies used in the study. Rows 1-5 correspond to the array positions listed in the

Sound Mapping and Acoustic Setup section above. Columns 1-5 correspond to the hydrophone

positions 1 through 5. The median was chosen as a robust statistic to compensate for outliers in

the data due to the dB scale. Further, the statistics were formed in the amplitude representation,

rather than in the dB representation, again to compensate for outliers. As an example of the bias

in the dB scale, the three amplitudes, 0.8, 1.0 and 1.2, have a mean of 1.0. Using the dB scale,

the respective dB values are -1.9382, 0, and 1.5836. The mean of these values is -0.118 which

corresponds to 0.986, different from 1. For small variations about the mean, the bias is not

important; however, when larger excursions (0.7 = about 3 dB) the bias is significant.

Table D1: Deviations from median for 600 Hz (mean deviation = -0.17, SD =1.1)

 0.53 0.7 0 0.25 -1

 1 1.4 0.51 0.6 -0.24

 -1.1 -0.69 -1.9 -1.9 -2.9

 -0.91 -0.48 -1.4 -1.1 -1.8

 1.2 1.3 0.73 0.93 0.18

Table D2: Deviations from median for 1000 Hz (mean deviation = 0.012, SD = 0.86)

 0.1 1.2 -0.47 0.5 0.19

 0.66 2.2 -0.34 0.32 0.13

 -0.95 0 -1.7 -0.79 -1.2

 -0.15 0.81 -0.98 -0.5 -0.86

 -0.4 1 -0.98 0.66 0.8

Table D3: Deviations from median for 1750 Hz (mean deviation = -0.13, SD = 1.3)

 1.4 -1.7 0.23 1.1 -0.8

 -0.14 -1.2 -1.9 -1.5 -3.1

 0.98 0.72 0.73 1.5 -0.59

 0.16 -0.32 0.18 1.1 -2.7

 2.8 0.18 -1.1 -2.1 0
51

Table D4: Deviations from median for 2420 Hz (mean deviation = 0.053, SD = 1.8)

 0.65 -2.4 0.2 0.83 -1.1

 0.49 -2.8 -1.3 0.37 -0.85

 3.2 0 2 3.5 -0.77

 2.8 -1.7 -1.7 0.92 -1

 -0.71 -2.4 0.54 1.5 -4

The table below summarizes the distribution for mean and standard deviation vs.

frequency when the median is chosen at 0 dB. As expected, the spread increases with frequency,

as do the outliers.

Table D5: Summary of Tables D1 –D4 showing overall mean and standard deviation by

frequency

Frequency Mean Sigma ±95%

 600 -0.17 1.1 2.2

 1000 0.012 0.86 1.72

 1750 -0.13 1.3 2.6

 2420 0.053 1.8 3.6

Initial placement of the sound projectors was determined by modeling efforts. Final

placement of the projectors was determined following preliminary sound mapping at several test

placements. The source placement chosen was designed to make the field most uniform at the

diver axis in the region of head and thorax. The summary below shows the pressures relative to

the median along this axis (array position 1) for the four frequencies for the final projector

configuration. The figures in red show the head and thorax region.

Table D6: Summary of the deviation in SPL (dB) relative to the median when the median is

chosen as 0 dB for array position 1 (along the long axis of the diver at 1.0 m depth) for each of

the test frequencies.

 600 Hz 0.53 1 -1.1 -0.91 1.2

 1000 Hz 0.1 0.66 -0.95 -0.15 -0.4

 1750 Hz 1.4 -0.14 0.98 0.16 2.8

 2420 Hz 0.65 0.49 3.2 2.8 -0.71
52

Appendix E

The computer generated randomized stimulus order matrix

Starting

Position

Frequency SPL

1 2500 154

2 silence

3 2500 166

4 1000 140

5 1000 166

6 2500 140

7 2500 148

8 1750 140

9 600 148

10 silence

11 1000 148

12 1750 148

13 600 154

14 1000 154

15 600 163

16 silence

17 1750 166

18 600 140

19 1750 154

Appendix F

Least Squares linear regression equations for loudness and vibration as a function of SPL for

each LFWBS frequency

Loudness ratings (see Figure 7)

Loudness at 600 Hz = 0.13 x SPL – 16.69

Loudness at 1000 Hz = 0.117 x SPL – 14.92

Loudness at 1750 Hz = 0.108 x SPL – 13.31

Loudness at 2420 Hz = 0.115 x SPL – 13.77

Vibration ratings (see Figure 9)

Vibration at 600 Hz = 0.039 x SPL – 5.44

Vibration at 1000 Hz = 0.016 x SPL – 2.09

Vibration at 1750 Hz = 0.013 x SPL – 1.67

Vibration at 2420 Hz = 0.02 x SPL – 2.73
53

Appendix G

Summary Statistics comparing pre and post dive performance on the ANAM 2000 Test Ba

Code substitution T-Test

Paired Samples Statistics

1126.8481 21 205.5243 44.8491

1062.7024 21 146.4903 31.9668

377.9724 21 152.3333 33.2419

394.7529 21 145.2910 31.7051

93.9776 21 5.6113 1.2245

95.7667 21 3.7121 .8100

51.5281 21 10.6135 2.3161

54.7148 21 8.0366 1.7537

PREMRT

POSTMRT

Pair

1

PRESD

POSTSD

Pair

2

PREACC

POSTACC

Pair

3

PRETP

POSTTP

Pair

4

Mean N Std. Deviation

Std. Error

Mean

Paired Samples Correlations

21 .817 .000

21 .174 .451

21 .910 .000

21 .846 .000

Pair 1 PREMRT & POSTMRT

Pair 2 PRESD & POSTSD

Pair 3 PREACC & POSTACC

Pair 4 PRETP & POSTTP

N Correlation Sig.

Paired Samples Test

64.1457 120.3916 26.2716 9.3441 118.9473 2.442

-16.7805 191.3500 41.7560 -103.8820 70.3210 -.402

-1.7890 2.7129 .5920 -3.0239 -.5542 -3.022

-3.1867 5.7402 1.2526 -5.7996 -.5738 -2.544

Pair 1 PREMRT - POSTMRT

Pair 2 PRESD - POSTSD

Pair 3 PREACC - POSTACC

Pair 4 PRETP - POSTTP

Mean Std. Deviation

Std. Error

Mean Lower Upper

95% Confidence

Interval of the

Difference

Paired Differences

t df

The following units are used throughout th

Mean Reaction Time (MRT) = ms

Accuracy (ACC) = % correct

Throughput (TP) = number of correct resp
54

Code substitution-short delay T-Test

Paired Samples Statistics

1254.8962 21 337.6896 73.6899

1149.0419 21 366.7014 80.0208

529.1224 21 382.7996 83.5337

469.8790 21 497.3355 108.5275

89.9467 21 11.9937 2.6172

91.7981 21 9.7207 2.1212

45.9638 21 13.7277 2.9956

51.7057 21 14.1271 3.0828

PREMRT

POSTMRT

Pair

1

PRESD

POSTSD

Pair

2

PREACC

POSTACC

Pair

3

PRETP

POSTTP

Pair

4

Mean N Std. Deviation

Std. Error

Mean

Paired Samples Correlations

21 .505 .020

21 -.066 .775

21 .528 .014

21 .627 .002

Pair 1 PREMRT & POSTMRT

Pair 2 PRESD & POSTSD

Pair 3 PREACC & POSTACC

Pair 4 PRETP & POSTTP

N Correlation Sig.

Paired Samples Test

105.8543 351.4598 76.6948 -54.1283 265.8369 1.380

59.2433 647.3986 141.2740 -235.4490 353.9357 .419

-1.8514 10.7337 2.3423 -6.7374 3.0345 -.790

-5.7419 12.0270 2.6245 -11.2165 -.2673 -2.188

Pair 1 PREMRT - POSTMRT

Pair 2 PRESD - POSTSD

Pair 3 PREACC - POSTACC

Pair 4 PRETP - POSTTP

Mean Std. Deviation

Std. Error

Mean Lower Upper

95% Confidence

Interval of the

Difference

Paired Differences

t df
55

Code substitution long delay T-Test

Paired Samples Statistics

1312.2219 21 342.4363 74.7257

1157.3081 21 337.5796 73.6659

592.1095 21 357.3633 77.9831

383.5186 21 182.2746 39.7756

87.0362 21 14.4149 3.1456

87.8290 21 13.3344 2.9098

42.0281 21 14.3514 3.1317

47.1119 21 14.2319 3.1057

PREMRT

POSTMRT

Pair

1

PRESD

POSTSD

Pair

2

PREACC

POSTACC

Pair

3

PRETP

POSTTP

Pair

4

Mean N Std. Deviation

Std. Error

Mean

Paired Samples Correlations

21 .545 .011

21 .060 .798

21 .551 .010

21 .534 .013

Pair 1 PREMRT & POSTMRT

Pair 2 PRESD & POSTSD

Pair 3 PREACC & POSTACC

Pair 4 PRETP & POSTTP

N Correlation Sig.

Paired Samples Test

154.9138 324.4986 70.8114 7.2038 302.6238 2.188

208.5910 391.3820 85.4066 30.4360 386.7459 2.442

-.7929 13.1788 2.8758 -6.7918 5.2060 -.276

-5.0838 13.7993 3.0112 -11.3652 1.1975 -1.688

Pair 1 PREMRT - POSTMRT

Pair 2 PRESD - POSTSD

Pair 3 PREACC - POSTACC

Pair 4 PRETP - POSTTP

Mean Std. Deviation

Std. Error

Mean Lower Upper

95% Confidence

Interval of the

Difference

Paired Differences

t df
56

Simple Reaction Time Dependent T-Test Results.

Paired Samples Statistics

256.2157 21 30.5741 6.6718

244.6448 21 27.6715 6.0384

68.3486 21 59.6678 13.0206

52.4267 21 24.3416 5.3118

237.3967 21 28.5963 6.2402

247.9281 21 25.2259 5.5047

PREMRT

POSTMRT

Pair

1

PRESD

POSTSD

Pair

2

PRETHRUP

POSTTP

Pair

3

Mean N Std. Deviation

Std. Error

Mean

Paired Samples Correlations

21 .673 .001

21 .596 .004

21 .682 .001

Pair 1 PREMRT & POSTMRT

Pair 2 PRESD & POSTSD

Pair 3 PRETHRUP & POSTTP

N Correlation Sig.

Paired Samples Test

11.5710 23.7103 5.1740 .7782 22.3637 2.236

15.9219 49.2163 10.7399 -6.4811 38.3249 1.483

-10.5314 21.6916 4.7335 -20.4053 -.6575 -2.225

Pair 1 PREMRT - POSTMRT

Pair 2 PRESD - POSTSD

Pair 3 PRETHRUP - POSTTP

Mean Std. Deviation

Std. Error

Mean Lower Upper

95% Confidence

Interval of the

Difference

Paired Differences

t df
57

Continuous Performance Test T-Test

Paired Samples Statistics

515.7233 21 55.7860 12.1735

491.9990 21 57.8453 12.6229

137.3905 21 30.3171 6.6157

137.8162 21 31.7585 6.9303

96.5033 21 2.0361 .4443

95.6005 21 3.3150 .7234

113.7986 21 12.6470 2.7598

117.8805 21 12.1525 2.6519

PREMRT

POSTMRT

Pair

1

PRESD

POSTSD

Pair

2

PREACC

POSTACC

Pair

3

PRETHRUP

POSTTP

Pair

4

Mean N Std. Deviation

Std. Error

Mean

Paired Samples Correlations

21 .744 .000

21 .375 .094

21 .514 .017

21 .622 .003

Pair 1 PREMRT & POSTMRT

Pair 2 PRESD & POSTSD

Pair 3 PREACC & POSTACC

Pair 4 PRETHRUP & POSTTP

N Correlation Sig.

Paired Samples Test

23.7243 40.6863 8.8785 5.2041 42.2445 2.672

-.4257 34.7250 7.5776 -16.2323 15.3809 -.056

.9029 2.8627 .6247 -.4002 2.2059 1.445

-4.0819 10.7936 2.3554 -8.9951 .8313 -1.733

Pair 1 PREMRT - POSTMRT

Pair 2 PRESD - POSTSD

Pair 3 PREACC - POSTACC

Pair 4 PRETHRUP - POSTTP

Mean Std. Deviation

Std. Error

Mean Lower Upper

95% Confidence

Interval of the

Difference

Paired Differences

t df
58

Matching to Sample T-Test

Paired Samples Statistics

1174.0171 21 238.3221 52.0061

1371.9976 21 453.5160 98.9653

360.3633 21 126.8660 27.6844

530.7629 21 546.5878 119.2752

95.8724 21 6.4898 1.4162

93.9676 21 8.4069 1.8345

50.9129 21 11.8797 2.5924

45.0090 21 14.4242 3.1476

PREMRT

POSTMRT

Pair

1

PRESD

POSTSD

Pair

2

PREACC

POSTACC

Pair

3

PRETP

POSTTP

Pair

4

Mean N Std. Deviation

Std. Error

Mean

Paired Samples Correlations

21 .787 .000

21 .353 .116

21 .091 .694

21 .731 .000

Pair 1 PREMRT & POSTMRT

Pair 2 PRESD & POSTSD

Pair 3 PREACC & POSTACC

Pair 4 PRETP & POSTTP

N Correlation Sig.

Paired Samples Test

-197.9805 304.0154 66.3416 -336.3666 -59.5943 -2.984

-170.3995 515.6226 112.5181 -405.1081 64.3091 -1.514

1.9048 10.1405 2.2128 -2.7112 6.5207 .861

5.9038 9.9319 2.1673 1.3829 10.4247 2.724

Pair 1 PREMRT - POSTMRT

Pair 2 PRESD - POSTSD

Pair 3 PREACC - POSTACC

Pair 4 PRETP - POSTTP

Mean Std. Deviation

Std. Error

Mean Lower Upper

95% Confidence

Interval of the

Difference

Paired Differences

t df
59

Math T-Test

Paired Samples Statistics

2255.1314 21 689.0928 150.3724

2116.8210 21 663.8208 144.8576

736.2481 21 357.7136 78.0595

725.7233 21 287.0323 62.6356

91.4286 21 7.7690 1.6953

91.1905 21 8.9310 1.9489

26.1486 21 8.6013 1.8770

27.5690 21 8.1100 1.7697

PREMRT

POSTMRT

Pair

1

PRESD

POSTSD

Pair

2

PREACC

POSTACC

Pair

3

PRETP

POSTTP

Pair

4

Mean N Std. Deviation

Std. Error

Mean

Paired Samples Correlations

21 .951 .000

21 .655 .001

21 .587 .005

21 .936 .000

Pair 1 PREMRT & POSTMRT

Pair 2 PRESD & POSTSD

Pair 3 PREACC & POSTACC

Pair 4 PRETP & POSTTP

N Correlation Sig.

Paired Samples Test

138.3105 212.6201 46.3975 41.5270 235.0940 2.981

10.5248 275.4163 60.1008 -114.8432 135.8927 .175

.2381 7.6610 1.6718 -3.2491 3.7253 .142

-1.4205 3.0264 .6604 -2.7981 -4.29E-02 -2.151

Pair 1 PREMRT - POSTMRT

Pair 2 PRESD - POSTSD

Pair 3 PREACC - POSTACC

Pair 4 PRETP - POSTTP

Mean Std. Deviation

Std. Error

Mean Lower Upper

95% Confidence

Interval of the

Difference

Paired Differences

t df