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Paps’ 37$

THE IMPORTANCE OF PROVIDING

STEREOSCOPIC VISION IN TRAINING FOR

c

~ 

NAP-OF~THE EARTH FLIGHT

Donald E. Erwin

L!VLL

ENGAGEMENT SIMULATION TECHNICAL AREA

U. S. Army

Research Institute for the Behavioral and Social Sciences

July 1919

for PUbH7Iig; dI tr~~yIo~~~ nUmIt.~

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1

U. S. ARMY RESEARCH INSTI T UTE

FOR TH E BEHAVIORAL AN D SOCIAL SCIENCES

A Field Operating Agenc y under the Jurisdict ion of the

Deputy Chief of Staff for Perso nnel

WILLIAM L . HAUSER

JO SEPH ZEIDNER Colonel . U $ Army

Tschn lcs l Director Commander

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~~~ TIIE JMPORTANCE OF.J.

ROVIDING ~ TERBOSCOPIC VISI0P -- \

~ ~1N T~AINING FOR NA~-OF-THE-JARTH FLIGHT . - _________________________

— S. PERFORMING ORG. REPORT NUMBER

7. AUTHOR(.) S. CONTRACT OR GRAM? NUNSE~~.)

Donald E.JErwin

] -- C. PERFORMING ORGANIZATION NAME AND ADDRESS tO. PROGRAM ELEMENT. PROJECT . TASK

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and Social Sciences ~ ‘2 16l1~~ A91B ‘7

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Approve d for public re e; distribution unlimited.

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17. DISTRIBUTION STATEMENT (of st~ . ~~~ ~~~~~~~~~ 1o;

~r . e...a~..u

IS. SUPPLEMENTARY NOTES

IC. KEY WORDS (C.otbiu . m~ .o .I

~~ SI ..o.oc y d Sd.,SIb’ Sy block m b.t)

Stereops is

Nap of the earth (HOE)

Helicopter simulators

5S *ae~R*c~

r ~~~~~ — .O~~~~~~ ~~~ V T ~~~ f

~~~ 55~ 

Ip kIosk ~~~~~ .,)

~~ ~ Alap—of—the—earth (HOE) flight in Army tactical helicopter operations

necessitates high speed visual—motor coord inations in order to avoid obstacle s

in the flight path while making as~~-f as*l use of the terrain for cover end concealment from enemy air defense weapon systems. The development of simolators

for training pilots in HOE flight involves the design of visual display sys— .

1

’

’

teas whi~ i provide all the important optical information available in actual ‘

flight. At the pres ent time, however, there is insufficient information on —-

~

(continued)

~~~ ‘~I W3 asseto. ~~ ~ ~~ ~~~~ ~~~~°‘~~~ ‘ Unclassified

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~ ametv ~~.MSPICATION OP TISIB PROC (

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Unclassified

Ii~ URITY CLA$SIFICA1IOM OF THIS PAG((RO~~ Dab 55AMs~

Item 20 (Continued)

0 the role of stereo psis in HOE flight to deter mine whether fully binocular

displays must be designed into training simulators.

This paper describes results from two preliminar y studie s which e~~~ fned

the importance of binocular disparity for the perception of three—di.snsional

layout of the terrain in HOE flight. In the first experi ment , it was determined that stereoscopic movies taken from the cockpit of a helicopter in HOE

r flight produce more compelling impressions of three —dimensionality then a

non—disparate bioptic display. The results of the second experiment show

that simple reaction times for detection of thre e—di.ensionality in static

binocular displays were substantially longer than for detection of fusibility

of othe rwise identical bioptic displays . ~~dditio nal1y, it was found that

detection of fusibility required much mor’è

~ time than detection of a light

flash . \

Strategies for further research bearir~ on a design recomeendat ion

are presented and discussed .

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Unclassified

SECURITY CLASSIFICATION OF THIS PAGE(Stt.n Dab. EMt.r.~~

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TEluik

~ Paper 37$

THE IMPORTANCE OF PROVIDING

STEREOSCOPIC VISION IN TRAINING FOR

NAP-OF•THE-EARTH FLIGHT

Donald E. Erwin

Robert T. Root, Team Chief

Submitted by:

Frank J. Harris, Chief

ENGAGEMENT SIMULATION TECHNICAL AREA

Approved By:

A. H. Bimbaum, ActlnQ Director

ORGANIZATIONS AND SYSTEMS

RESEARCH LABORATORY

Joseph Zeidner - TECHNICAL DIRECTOR

US. ARMY RESEARCH INSTITUTE FOR ThE BEHAVIORAL AND SOCIAL SCIENCES

5001 Eiaunhomsr Avenue, Alexandria, VirgInia 22333

Off Ice, Deputy Chief of Staff for Personnel

D.pertm.nt of the Army

July 1979

Army Project Number Tactical Skill AcquIsItion

20161101A91B IL Retention

Appro.d for public ,ale..e; dIetribitlon unUedtsd~

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• ARI Ressardi Reports and Technical Pepess are intended for sponsors of

R&D taslis and other research and military agencies. Any findings ready for

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rime of pu blication ass aenP~

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the Brief. Upon completion of a major phase of the task, formal recommenda’Jons for official action normally are conveyed to eppropriate military

agencies by briefing or Disposition Form.

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L. . _

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FOREWORD

This research was performed under the in—house laboratory independent research (ILIR) program in FT 1978 of the Army Research Institute for the Behavioral ~~d Sucial SciencU. Dr. Aaron Hymen ’s contribution was integral to this work; he provided much of the technical

expertise needed to conceive and construct a working hypothesis in the

problem area and to indicate the direction that further research would

have to follow. The results have also been discussed in a symposium

entitled “Display Modes and Dimensions” at the national Human Factors

Society meeting in 1978.

SEPH

ethnical Director

I

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THE IMPORTANCE OP PROVIDING STEREOSCOPIC VISION IN

TRAI1!~~ FOR NAP-OF-THE-EARTH FLIGHT

BRIEF

Requirement:

Nap—of—the—earth (NOE) helicopter flight requires high speed visualmotor coordination in order to avoid obstacles in the flight path ~

while

making maximum use of terrain for cover and concealment from enemy air

defense weapon systems. The development of simulators for training

pilots in NOE flight has generated the question of whether or not stere—

optic visual displays would be more cost and training effective than the

bioptic displays usuall y employed In aircraft simulators. The purpose

of the present study was to address this question and identif y the research required to determine if stereoptic displays should be developed

for helicopter simulators.

Procedure :

Stereoscopic movie f ilms were taken of passing terrain through the

cockpit of an 051—58 flying NOE at speeds of 20, 40, and 60 knots. Observers compared stereoscopic presentations of the films to bioptic -presentations and found the depth perceived in the stereoscopic film much

more compelling. This study demonstrated that it is possible to perceive

stereoptic three—dimensionality with the stimulus environment available

through the wind screen of - a helicopter flying NOE . Observers were then

asked to make motor reaction times when they perceived three-dimensionality in stereosco pic slides of wooded terrain . These reaction times

were compared to motor reaction times to binocular fusion and a simple

flash of light to determine if the perception of stereoscopic three—

dimensionality has a measurable “rise time.” A “rise time” of approxi- mately 400 macc was measured . Ca t ch trials were used to insure that

observers waited until three—dimensionality or fusion was perceived

before responding. This result suggests that a discrete interv al is

required after “seeing” something to perceive stereoptic three—d imension— ality, and, this interval may or may not be available to observers

depend ing on the rate at which they scan the visual stimulus environment .

Findings and Conclusion s:

At the rate with which pilots flying NOE must scan the visual

stimulus environment , and , the variou s other attentiona l load s resulting from co~~ inications and avionics syste~ s, stereoptic depth perception
- - -

may not occur . Although it is theoretica lly possible , as demonstrated

in the laboratory , actual flight conditions may interfere with the

development of stereoptic three—d imenaionality. Consequently, pilots

flying NOE may perceive depth bioptically. If this is the case, stere—

optic visual displays in NOE simulators would be inappropriate. To

determine if stereoptic displays should be developed for flight simulators, five research questions must be addressed :

(1) At what rate do pilots scan the stimulus environment?

(2) Is stereoptic depth perception associated with signif icantly

more prof icient psychomotor performance?

(3) Are there attentio nal requirements in NOE flight that can

significantly lengthen the rise time for the percep tiot of

stereoptic three—diiaension.ality?

(4) Can bioptic depth information be used as effectively?

(5) Is a stereoptic display more coat—effective than extra time

in the aircraft?

Utiliz ation of Findings :

Before proceeding with technological feasibility studies of stereoscopic visual displays for helicopter simulators, the research questions

outlined in this report should be addressed to determine if helicopter

pilots see stereoptic as opposed to biopti~ depth . This report sharpens

the focus and makes more explicit the research requirement on “stereo

displays” outlined in the Five Year Development and Management ?lar~ for

Flight Simulat ion publishe d by - the Army TrainF~

g Device Agency in 1975.
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THE IMPORTANCE OF PROVIDING STEREOSCOPIC VISION IN TRAINING

FOR NAP-OF-ThE-EARTH FLIGHT

CONTENT S

Page

INTRODUCTION 1

RESEARCH RESULTS 5

Project I 5

Project II 6

STRATEGIES FOR FURTHER RESEARCH 9

Strategy A . 

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9

Strategy B 10

Strategy C . . . 11

Strategy D 11

Strategy E 12

CONCLUSIONS AND IMPLICATIONS 12

REFERENCES 13

DISTRIBUTION 15

LIST OF FIGURES

Figure 1. Nap—of—the—earth helicopter flight . 1

2. Bioptic visual display in flight simulation . . . 3

3. Stereoscopic visual display in flight simulation . 4

4. Project I 6

5. Proj ect II . . . 7

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THE DIP0RTANC~ OF PROVIDING STEREOSCOPIC VISION

IN TRAINING FOR NAP—OF-THE-EARCH (NOE) FLIGHT

INTRODUCTION

Current U.S. Army doctrine on tactical helicopter operations states

unequivocally that if the likelihood of contact with the enemy is “possible” or “expected” , both scout and attack helicopters should fly “nap—of—the—earth” (NOE) whenever possible (Figure 1) (US Army Armor

LOW-LEVEL

Altitude Con,tant ~~~~~~~~

— 

Alrsp..d Constant —

CONTOUR - 

- 

-

AItit

~~

e Variabli -

Airsp.ed Constant ____

NOE

Altitud Variable

Airspeed Variable

Figure 1. Nap—of—the—Earth Helicopter Flight

SchooL, 1975). NOE flight is currently defined as flying as “close to

the earth’s surface as vegetation or obstacles permit, while generally

following the contours of the terrain. In flight, the helicopter pilot

uses a weaving route within a prep ].anned corridor. . . in order to take

maximum advantage of the cover and concealment afforded by terrain, vegetation, and man—made features . The restrictive nature of this type

of flight demands almost instantaneous reaction from the flight personnel involved “ (US Army Train ing Device Agency , 1975) .

1

~~~~~ ~~~~ - J— -~~ -~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ _ _—.
.-— - - -----~~~.-- ~~~~~~~~~

NOE flight is demanding both psychologically and physically. The

threat during NOE flight is, in a sense, two—fold. The pilot is forced

to pay constant attention to oncoming and passing terrain and execute

motor responses qu ickly enough to avoid obstacles and make maximal use

of changes in the terrain to hide his aircraft. The pilot must also

attend to the amount of time he stays unmasked at any given location :

15—20 seconds is just about enough time for acquisition and engagement by

most anti—aircraft guns and short range missile systems. The pilot must

respond to two threats: terrain and the en~~iy. That threat of most immediate concern to the pilot in the tactical environment requiring NOE

flight is, of course, the terrain. If he can successfully cope with the

perceptual and mot

~tic demands of NOE flight , then he has significantly

reduced the probability of being unexpectedly acquired and engaged by air

defense weapon systems.

ft NOE helicopter flight , the pilot is assisted to a small extent by

his instrument panel but he relies primarily on visually monitoring the

oncoming and passing airspace for cues indicating how and when he should

change the disposition of the aircraft. A recent task analysis of NOE

flight (Gainer and Sullivan, 1976) indicates that for the task of “monitor

air space” in which the operator must observe terrain and airspace below

the helicopter to identify potential flight hazards and remain below

surrounding terrain features, the only stiim*lu s input is the external

visual display. To detect, identify, and evaluate airspace and terrain

objects and features that could become potential flight hazards is solely

the task of the pilot as he visually monitors the world outside the aircraft. There are no controls or displays available to aid him in this

task. Daytime NOE flight , then , is a purely “heaäs—up ” flying situation

requiring a high degree of perceptual/motor coordination . Minimum proficiency in obstacle avoidance may be acceptable from a safety point of

view, but high proficiency is necessary for NOE flight that is both safe

and tactically acceptable. This distinction between minimum and high

proficiency is a critical one. In the two World Wars , the probability

that a pilot would be killed in a combat mission was reduced by a factor

of 20 if tI~

e first five missions were survived. And , 4% of the pilots

have produced 40% of the kills in every war since WW I. (Merrit and

Sprey, 1972). The goal of minimally adequate performance after training

is becoming more and more widely considered as unacceptable in training

pilots in combat aircraft .

For NOE flight training, the US Army has begun to procure flight

simulators for attack and scout helicopters. The two driving forces for

research, design , and procurement of flight simulators are that they are

more cost—effective, and theoretically, more training effective than

actual flight training.

In existing simulators for the attack helicopter, terrain model

boards with optical probes are used for presenting a visual display to

the pilot/trainee. The display originates via high reso1ut’L~~. closed

2
circuit color television and is 48° horizontal by 36° vertical • The

viewing position and directed lines of sight are controlled by the simu—

lat ion computer to precisely track the simulated aircraft in all six

natural degrees of freedom relative to the geographic location and

orientation of the modeled area .

The pilot/tra inee sees only one image of the area scanned by the

optical probe: it is as if the pilot were monitoring ~ne airspace and

terrain with only one eye, as shown in Figure 2 • The trainee , when flying

MODEL BOARD

ONE PICTURE OF MODEL TERRAIN

OPTICAL PROBE BIOPTIC SCENE PRESENTED

TO THE OBSERVER

Figure 2. Bioptic Visual Display in Flight Simulation

the simulator, has bioptic, as opposed to stereoptic , vision . The U.S.

Army is not sure precisel y what impact this sort of visual environment

has on the training effectiveness of the simulator. If one of the reasons

for building flight simulators is to train highly proficient pilots, and

the visual display in the simulator does not allow the pilot/trainee to

develop and prac tice certain critical perceptual/motor skills that may be

dependent upon stereoscopic perception , then there is a design deficiency

in the simulator.

An atte mpt is being made to determ ine if stereoptic vision significantly contributes to the helicopter pilot’s ability to “ . . . evaluate airspace and terrain objects and features that could become potential flight

3 

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hazards and/or unmask the aircraft “ (Gainer and Sullivan, 1976) . If

stereoscopic vision can be shown to be critical in facilitating maximally safe and tactically proficient NOE flight skills, then the importance of a stereoscopic display for NOE flight simulators will have been

demonstrated (Figure ~~). The next requirement will be to determine what

sort of displays are technologically feasible for use in the simulator.

MODEL BOARD

Two PICTURES OF MODEL TERRAIN

- OPTICAL PROBE STEREOPTIC SCENE PRESENTED

TO THE OBSERVER

Figure 3. Stereoscopic Visual Display in Flight Simulation

This research question is stated explicitly in an exploratory re- search and development program outlined for Army flight simulators by the

Army Training Device Agency entitled , “Nap—of— the— Earth Technology Study” which is appended to the Five Year Development and Management Plan for

Flight Simulation (Army Training Device Agency , 1975) . The following

statement presents the research requirement:

The perception of distance and depth is vital in the judgement

of terrain contours during NOE flight. Conventional two—dimensional display systems do not permit the human operator to make

full use of a highly refined sense of depth. With depth added

to the display, the operator will be able to perform more eff i—

ciently by taking advantage of depth perception capabilities.

4

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Recent ly conducted research indicates that the use of stereo

television disp lays permit more efficient low-altitude , terrain—

following flight. Whether stereo displays would permit improved

operator performance during NOE flight is a question , as yet ,

not fully answered . Also not certain is whether flight training

simulators could be adapted for stereo display if such were found

to provide an advantage in NOE flight. The NOE technology study

would be directed toward obtaining data applicable to answering

both of these questions.

The research reported in this paper bears on the first of these

two areas.

RESEARCH RESULTS

The basic objective of the research program is to determine if a

recoemendation should be made that stereoscopic displays be developed for

helicopter simulators in which the pilots can train for NOE flight. There

are a number of questions that have to be answered before this objective

can be met and the research program described here has begun to look at

• the most basic of these questions: Does the helicopter pilot use stereoscopic vision in analyz ing and responding to the visual environment

during NOE flight?

Project I

The initial work on this question involved the development and

evaluation of a dynamic stereoscopic display system. An Arriflex two

perforation pull-down 35mm ciiie camera with a stereoscopic lens system

was used to collect approximately 1000 ft. of through—the—cockpit stereo

film of an OR—58 Scout helicopter flying NOE at speeds of 20 , 40 , and 60

knots. The film was collected at the NOE flight training area of the 3d

Armored Cavalry Regiment at Fort Bliss, Texas. Each frame of the film

contains two 600 diameter circular images that approximate the pair of

scenes available to the pilot as he flies NOE and looks through the

windscreen. When the images are projected to the appropriate eyes using

the technique of crossed polarizing filters, observers perceive three—

dimensionality as the aircraft moves along the terrain, 3 or 4 feet above

the ground, at speeds of 20, 40, or 60 knots. This display is presented

schematically in Figure 4.

Observers report that the impression of three—dimensionality is. much

more compelling with a stereoscopic presentation than with a bioptic

display, in which the observer looks at only one of the two 600 diameter

images with both eyes.

The purpose of this exercise was to try to determine quickly and

inexpensively if a pilot flying NOR perceives depth , and if he does, is

stereoscopic depth more compelling ~

:han biop ic depth in a dynamic real—

5

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j
world display, After a number of observers had viewed the displays,

it was posøible to conclude that they are able to perceive compelling

three—diaensionality when one has a stereoscopic view of the world while

moving along NOR terrain at 20 , 40, or 60 knots,

0 THROUGH—THE—WINDSCREEN MoVIE Fiui

• 

o STEREO DIsPI..Av vs. BI0PTIc Dis~i~v

600 VA

Is IT POSSIBLE TO PERCEIVE STEREOSCOPIC THREE—DIMENSIONALITY

DURING NOE FLIGHT?

Figure 4. Project I

It was also possible to demonstrate that standard 35em color negative

cine film could be used to provide dynamic stereoscopic views of the

visual environment, that airborne f41.tng with stereo cine equipment can

provide dynamic stimulus material for experimental studies of depth per—

ception during HOE flight, and that the prototype lens system used both

as a taking and projection lens and mated with a shoulder—mounted c~~~ra

was a low-cost, feasible alternative f or collecting stereo cine film

compared to synchronized , shock—mounted cine or videotape camera systems.

Project II

The stereoscopic cine film demonstrated that pilots flying HOE at

20, 40, or 60 knots at least have the cues available for the development

of stereopsis: observers are able to perceive three-di.ensionality when

viewing the film. But the question remains, are pilots forced by NOR

flight conditions to monitor the visual environment at a rate or with

various attentional requirements that might prevent the development of

the perception of three—diaensionality, and utilization of stereoscopic

6

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- -- 

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ • - ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ - - -if -

cues for depth perception takes an appreciable amount of time , the rate

at which the pilot flying NOR has to scan the visual world may militate

against the development and use of obstacle avoidance information avail—

able by three—dimensional, stereoscopic perception.

The research discussed in this section was designed to determine

if three—dimensional stereoscopic perception takes a significant amount

of time and what is the approximate time relative to that required for

binocular fusion. Data from two experienced observers is discussed for

static displays of real—world scenes.

Methodology. Observers were seated at a response console in front

of a rear projection screen and were instructed to rest their forearms

on the table and use their thumbs to activate left and right micro—

switches, as shown in Figure 5.

MICRO SWITCHES

~~~~~

I \.

~.,,_,_ / 3) THREE-DIMEN5IONALITY

PROJECTORS REAR (OBSERVER GIVEN 1050 SCENES)

PROJECTION

SCREEN

Figure 5. Proj ect II

Observers were instructed that there were three conditions: (1)

Si~~le Reaction Time • In this condition, observers merely had to release

the aicroswitch when a white light appeared on the screen . For one set

of trials, observers responded with their left hands, and in a second

7

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—•—----‘— - - .—. •—--- — — -- • ---- - i-— •

set, with their right hands. There were four different exposure durations: 5, 4 , 3, and 2 seconds with ten trials per band per exposure

duration. (2) Binocular Fusion: In this condition, observers were

instructed to release the microswitch as soon as they saw one imag. on

the screen . Two sets of 12 trials were used , one set per hand. Two

• out of the 12 trials were “catch” trials; i.e., binocular fusion was not

possible. Observers were told that if it was not possible to fuse the

two images, they should not respond. Again, four exposure durations

• (5, 4, 3, and 2 seconds) were used . (3) Three—dimensionality: In this

condition , observers were told to release the microsvitch when they saw

• “3—D”. Again, 12 trials for left and right hands were given, with two

catch trials per set, for four exposure durations (5 , 4 3, and 2 seconds) . In the catch tr~a1s, the observer was able to fuse the two scenes

but the slides were not stereoscopic views. Observers were instructed

not to respond if they did not see

The same slides were used for the Binocular Fusion and Thres—dimensionality conditions. Various views of a forest scene were the

stimuli, with heavy foliage at ground level surrounding a cleared path

running from foreground to background . The Binocular Fusion slides

were merely two identical slides of a given scene. Observers could of

course fuse the two images but the perception of tbree—dimensionality

via stereoscopic views was not possible. In the three—dimensionslity

condition, each view of the forest was comprised of a stereoscopic slide

pair so that the perception of three-dimensionality was possible.

Observers were practiced on each of the three conditions. Both

observers had normal vision.

Results. The two observers required an average of 276.1 macc

(SD”30.3 mace) to make the simple reaction time with their right hand

and 248.6 macc with their left hand (SD—4l.4 macc) . Responses in the

Binocular Fusion condit ion were 670.6 macc for the right hand (SD—l14 .2

macc) and 771.3 macc for the left hand (SD—l89.3 msec), Responses in

the 3—D condition averaged 1036.8 for the right hand (SD 264.3 macc) and

1114.0 for the left hand (SD—256 .7 macc) . There were no systematic

differences among mean reaction times for the different exposure durations.

From these results, it seems reasonable to infer that the perception of three—dimensionality based on stereoscopic cues in real—world

scenes takes some finite amount of time past the occurrence of binocular

fusion. A motor reaction to the stereoscopic perception of three—di—

mensionality in a static display appeared to take at least one second

in the two observers studied . If this reaction in and of itself requires about 200—250 macc to execute, it is not wholly unreasonable to

suspect that the perception and reaction to three—d iaensionality takes

600—800 macc.

8 

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- a

These results have important implications for the question of

whether or not pilots flying NOR have sufficient time to perceive a

stereoscopic , three—dimensional world while they are flying, or , if

their impression of and reactions to depth depend on the bioptic

characteristics of the visual world. We can be relatively sure that in

fixed wing aircraft , which operate at much higher speeds, pilots do not

have ample time to resolve and utilize stereoscopic cues for depth . In

a helicopter flying NOR , however , when obstacle avoidance occurs at

speeds of 20—60 knots, and, tolerances are much closer due to the tactical requirement to stay as close to the terrain as possible, pilots

may indeed have the time and the requirement to utilize stereoscopic

information for depth.

Further research in several areas is required . First , at what

rate does the pilot flying NOE scan the visual environment? Is it at a

rate that prevents the development of stereoscopic perception and utilization of that information? Second , is stereoscopic perception associated with significantly more proficient psychomotor performance of

the kind critical for obstacle avoidance? Third , are there attentional

requir ements in tactical NOR flying that interfere with the utilization

of stereoscopic information? Fourth, are there strategies for more effective bioptic depth information utilization that can be trained in

the flight simulator which represent a more cost and training effective

alternative than providing a stereoscopic display? Fifth, do pilots

learn to use stereoscopic depth information as efficiently as possible

with in severa l hours of actual NOE flight so that provision of this

capacity in a simulator could more cost effectively be replaced by

several extra hours of actual flight training time?

These questions are discussed in more detail below.

STRATEGIES FOR FURTHER RESEARQI

Research completed to date has demonstrated that observers can see

three—d iaensionality during MOE flight and that stereoscopic displays

are noticeably more compelling than b ioptic dilplays, and that the

stereoscopic perception of depth in static real—world displays requires

a finite amount of time beyond the latency for binocular fusion.

Strategies for further research basically revolve around determining if

pilots flying NOR use stereoscopic depth information which makes them

more proficient on obstacle avoidance , and , if stereoscopic information

during training in a flight simulator is more cost— and training— effective than using an aircraft or a part—task training device.

Strategy A

To determine if MOE flight allows the pilot to scan the visual en—

vironment at a rate allowing the temporal development of stereoscopic

depth peTception and utilization of stereoscopic information, two studies

L 

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need to be done . First , pilots’ eye movements and f ixation rates when

flying. NOR have to be determined. The most feasible research strategy would be to record pilot eye movements in the attack helicopter flight simulator scheduled for operational testing at the U .S. Army Aviation

School at Fort Rucker, Alabama . Intrusive measurements, such as

electromyographie recordings, during actual NOR flight are too much of

a hazard for the pilot in terms of distractions and interference with

usual headgear and cockpit configuration.

The inf9rmation on fixation rate and duration could be correlated

with specific types of terrain if NOR courses are clearly marked on the

model board in the simulator . This information would in turn have to

be matched to the results of a study in which pilots are required to

make absolute and relative distance judgements for static real—world

stereoscopic displays of different exposure durations. Earlier research

has indicated that stereoscopic depth perception requires a discrete

amount of time after binocular fusion . Presumably, judgements of relative and absolute distance to targets in a stereoscopic display should

be very poor for exposure durations less than this time. Operating

speeds and/or terrain types that require pilot eye movements and scan

rates that yield fixations shorter in duration than that required for

stereoscopic perception would most probably be attended by bioptic as

opposed to stereoptic depth perception.

A parametric study to determine when distance estimation stabilizes

relative to exposure duration would indicate the minimu* duration required for the successful utilization of stereoscopic information. It

is difficult to predict the shape of the curve relating distance judgeaents to exposure duration, but if stereoscopic information does represent a significant factor in this ability, there would be a discrete

point at which performance markedly improves and stabilizes. If this

minimum exposure duration is very much greater than the amount of f ixation time observed in most pilots’ visual processing of the NOE environment, then the inference can be made that helicopter pilots flying HOE

probably do not “see” , much less use, stereoscopic depth information . This finding would provide compelling evidence that a stereoscopic display in a flight simulator is not a critical requirement .

Strategy B

In addit ion to determining if pilots do perceive their visual

environments stereoscopically , it is necessary to determine if more

proficient psychomotor performance associated with obstacle avoidance

results from utilization of stereoscopic depth perception . A study

using the stereoscopic cine display system described earlier would seem

to be the simplest and least costly approach to this problem. Films

taken through the windscreen of an aircraft flying at and then over

various obstacles could be used as stimulus materials, Pilots used as

10

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~fl ; : • — - — - —~~~~~~ - -

subjects would be required to make hand and/or foot responses similar

to those required to maneuver an OH or AR type helicopter away from

the obstacle. The same system lag characteristics as a helicopter

would be built into the response mechanisms so that the pilots would

face basically the same psychomotor task as in flight. By making f ilms

in an aircraft flown by a highly proficient pilot instructed to fly

safely but with tolerances that are tactically acceptable, stimulus

materials that represent criterion performance will be available , By

requiring the pilot to avoid obstacles in the film, and then blocking

out the display after the obstacle avoidance response, the problem of

the subject seeing when criterion performance (i.e., the “optimum”

obstacle avoidance performance shown in the film) occurs is avoided .

Dependent variables such as the number of trials to criterion, or, macc difference from criterion could be recorded for the independent

variables of NOE speed, type of obstacle, and stereoptic versus bioptic

display. If there are no differences between stereoptic and bioptic

displays, then evidence against the inclusion of stereoscopic displays

in training simulators is presented. That is, if pilots succeed in

using depth information from bioptic displays as efficiently and eff cc—

tively as stereoptic displays, then there is really no benefit derived

from including stereoscopic displays in training simulators, or developing a part—task simulator.

Strategy C

If evidence is obtained that pilots flying MOE can in fact use

stereoscopic information for obstacle avoidance, and when doing so, can

avoid obstacles more efficiently and effectively, then a determination

has to be made if there might be conditions in tactical NOR flight that

interfere with the utilization of stereoscopic depth information. Fo~ example, does the requirement to monitor communications or divide attention between flying the aircraft and using weapon systems coimeand suff i—

cient attentional or information processing capacity to interfere with

processing of stereoscopic information?

This question could easily be resolved using the procedures described for Strategy B but including additional attentional and/or

memorial tasks, such as monitoring and responding to a tap e recording

of communications, or having to remember and respond to specific obstacles as targets or key locations. Under conditions of tactical MOE

flight , processing of stereoscopic information for depth may be superseded by less “time—consuming” or “simpler” cues for depth. If so, the

importance of a stereoscopic display in a flight simulator designed to

train safe and tactically acceptable MOE flight skills may be questionable.

Strategy D

It may be possible to train MOE pilots to use bioptic information

more efficiently in their visual environment • This would be especially

important If Strategy C indicates that there are NOR flight conditions

11
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that interfere with the utilization of stereoscop ic information ,

Training strategies for efficient bioptic depth perception may do more

to facilitate obstacle avoidance performance than a stereoscopic display

that is really not representative of the visual environment available

to the pilot during tactical MOE flight. For e~

wample, repeated runs at

obstacles on the model board with performance feedback given per run

may give - the pilot a more accurate picture of precisely what his bi—

optic depth estimation abilities are for different speeds. A carefully designed training program with the objective of giving the pilot

an accurate awareness of his capacity and limitations for depth percep—

tion may be far more important than a stereoscopic display in the training simulator. The visual display in the flight simulator must match

the pilot’s real—world visual environment. It is certainly conceivable,

via—a—via Research Strategies A—D, that pilots flying in NOR do not

actually have stereoscopic depth information available to them for

either cognitive or visual reasons or both.

Strategy E

Criterion obstacle avoidance capability dependent on stereoscopic

depth perception may occur after a very short time in the aircraft, in

which case building a stereoscopic display system may not be the most

cost—effective training alternative. If Research Strategies A, B, and

C demonstrate that stereoscopic depth perception is a critical component

of high proficiency obstacle avoidance in MOE flight, then it would be

necessary to determine whether or not a stereoscopic display in the

simulator is more cost—effective than several hours of flight time . A

study comparing time and cost requirad for achievement of criterion

performance in actual flight and in a part—task training device simulating the stereoscopic display in the training simulator would have to

be done. In that the development of stereoscopic display capability

for a helicopter simulator would represent a significant research and

development effort, this comparison would have to be made.

CONCLUSIONS AND IMPLICATIONS

It would be premature to begin-to develop a display capability for

presenting stereoptic information in an helicopter flight simulator

without research to first determine if stereoptic depth information is

important for proficient obstacle avoidance, and , if pilots have the

“time” and/or attentional capacity to develop stereoscopic three—

dimensionality. Preliminary research on this problem has provided some

research tools and methodologies, and has served to define various

problem areas and considerations.

Too often in the simulation of work environments, the operational

environment is physically replicated without consideration of what the

psychological reality of that environment is for the operator. That is,

12 
r

in an operational situation, the pilots’ attentional, visual, and motor

capabilities may be continuously directed at only a very small subset of

the total possible stimulus environment. For training simulation, replication of these stimuli and the behavioral contingencies that attend

them is the design requirement——not the replication of the total stimu—

lus environment. In the case of the helicopter flight simulator, it is

necessary to determine precisely what would be psychologically real for

the pilot/trainee in the operational environment and include that in

the flight simulator if and only if it significantly contributes to

performance and is more cost—effective than flight training. The

engineer and human factors psychologist must often resist the temptation

to build what they consider to be a high fidelity physical replication

of the operational environment without adequate consideration of the

psychological reality, the psychological fidelity, of the training

simulation. -

REFERENCES

Gainer, C. A. and Sullivan, D. J. Aircrew task analysis and training

objectives for Nap—of—the—earth flight. ARI Research Memorandum

76—2 , 1976.

Merritt, 3. and Sprey , P. Quality , quantity, or training? Paper

presented at the Inter—Service Conference on Defense Policy ,

U.S. Air Force Academy , 1972.

U.S. Army Armor School. Attack Helicopter Operations, Field Manual

17—50, l97~ .

U.S. Army Training Device Agency. Army Aviation Flight Training Simulation Development and Management Plan: FY 1976—1980, 1975.

13

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