Naval Submarine

NSMRL REPORT 1170

Medical Research Laboratory

14 MAY 1991

THE EFFECT OF BLINKING ON SUBSEQUENT DARK ADAPTATION

by

S. M. Luria

Released by

R. G. Walter, CAPT, DC, USN

Commanding Officer

Naval Submarine Medical Research Laboratory

Approved for public release; distribution unlimited
THE EFFECT OF BLINKING ON SUBSEQUENT DARK

ADAPTATION

S.M. LURIA

Naval Submarine Medical Research Laboratory

Report Number 1170

U.S. Coast Guard

Work Unit NIPR-Z51100-9-0002

Approved and Released by:

R. G. Walter

Commanding Officer

Approved for public release; distribution unlimited
SUMMARY PAGE

The Problem

To test whether or not an initial period of blinking facilitated subsequent dark

adaptation.

The Findings

Blinking did not appreciably improve the speed of dark adaptation for any one

of 10 subjects. It somewhat interfered with the course of adaptation of three

subjects, because it produced an afterimage of the light adaptation screen.

Application

Blinking will not significantly reduce the time required for dark adaptation.

ADMINISTRATIVE INFORMATION

This investigation was conducted under U.S. Coast Guard Work Unit No.

NIPR-Z51100-9-0002. It was submitted for review on 5 September 1990, approved for publication on, and has been designated as Naval Submarine

Medical Research Laboratory Report Number 1170.

ii
Abstract

This study tested whether or not dark adaptation is facilitated by blinking for a

short time at the beginning of the dark adaptaion. The course of dark adaptation was

measured for 10 subjects both with and without an initial period of blinking for 30

seconds. The blinking did not improve the rate of dark adaptation.

iii
The Effect of Blinking on Subsequent Dark Adaptation

INTRODUCTION

Night vision is extremely important

for all operational forces, no less so for

the submarine force. Periscope operators

must be able to see at night, and great

care is taken to ensure that they will be

dark adapted when necessary. The crew

in the control center routinely begins to

dark adapt well in advance of nightfall.

It is, thus, impossible to imagine that a

submariner will not be dark adaptated

when necessary.

Nevertheless, if the dark adaptation

process could be speeded up, it would

add to the efficiency of submarine operations. For this reason, a claim by

Stryker (1990) that an individual will

achieve dark adaptation very quickly if

he blinks his eyes rapidly and forcefully

for 15 to 30 seconds has aroused some interest. The claim was that this technique works for about half of those

individuals who have tried it. The Commander of the U.S. Submarine Force in

the Pacific informally requested an

evaluation of this claim by NSMRL

(Goad, 1990).

There does not appear to be any compelling physiological basis for expecting

blinking to facilitate dark adaptation.

Dark adaptation has an initial very

rapid (1 or 2 seconds) neurological component (Baker, 1963) followed by a slow

biochemical component (30 to 45

minutes) (Rushton, Campbell, Hagins

and Brindley, 1955; Wald, 1959). The

former does not require 15 seconds or

more to be affected, and it is difficult to

see how a biochemical reaction--the

transformation of the photochemical

rhodopsin in the photoreceptors-- could

be speeded up from several minutes to

several seconds. It is conceivable that

energetic blinking might increase the

flow of blood, but this should not affect

the chemical transformation of the

rhodopsin.

There is one interesting phenomenon

which relates to Stryker's technique. It

is well known that an afterimage which

has faded can be brought back by blinking (Troland, 1917; Brindley, 1962; Barlow and Sparrock, 1964). The

explanation is not clear. But any technique which reintroduces afterimages

should elevate visual thresholds and interfere with dark adaptation rather

than facilitate it. In this study, we have

compared the rate of dark adaptation

with and without a preliminary 30-

second period of blinking.

METHOD

Subjects

Ten staff members of the laboratory

(eight men and two women), aged 21 to

60, served as subjects. All had or were

corrected to at least 20/25 vision. Most

had considerable experience as experimental observers.

Apparatus

The test light was a circular stimulus

subtending 30 min visual angle at the

viewing distance of one meter. It was

presented 10 deg to the left of a pinpoint red fixation light. The light source

was a projection bulb whose luminance

was varied with neutral density filters;

1
its dominant wavelength was adjusted

to 500 nm with a Corning glass filter.

The test light was exposed for 0.5 sec intervals with a Lafayette Tachistoscope

Shutter attachment, Model 43010. The

subjects were light adapted to a ground

glass screen illuminated to 500 C/m2

and subtending 40 deg visual angle on a

side.

Procedure

The subject was first light adapted for

three minutes. The lights were extinguished, and one of two procedures was

followed. Either he (or she) stood quietly

in the dark and looked downward for 30

seconds or else was instructed to look

downward and blink rapidly and forcefully for 30 seconds. Then he sat down,

occluded his left eye, placed his chin in a

chin-rest, and acquired the fixation

light. The experimenter then called out

two time intervals in close succession

and exposed the test stimulus for 0.5 sec

during one of them. (The subject could

hear the shutter being opened during

both intervals, but the light was blocked

during one of them.) The luminance of

the test stimulus was initially set below

his threshold, and this procedure was

repeated at 15 sec intervals until the

subject reported that he could see the

stimulus and reported it in the correct

interval. The luminance of the test

stimulus was then lowered, generally by

0.1 log unit, and the procedure was

repeated. This was continued for 15

minutes. Each subject was tested twice,

once after blinking and once without the

blinking. Half the subjects were tested

first without blinking; the other half

were tested first after blinking.

RESULTS AND COMMENT

Figure 1 shows the dark adaptation

curves with and without the blinking

for each subject. The subjects are in

order of age from KJ, the youngest to

SL, the oldest. Each graph shows the

time required by each subject to see the

test stimulus at a progressively reduced

luminance level. The lower and steeper

the curve, the more sensitive and faster

the subject is dark adapting. If the blinking facilitated dark adaptation, that

curve (filled circles) would be lower than

the curve obtained with no blinking

(open circles). If the blinking produced

complete dark adaptation in 30 seconds,

then its curve would be a horizontal line

at the lowest intensity which that subject was capable of seeing. To test if the

regression lines were significantly different, Z-scores were calculated for both

the intercepts and slopes (Cohen and

Cohen, 1983).

There is little indication that the

blinking reliably facilitated the dark

adaptation. The dark adaptation curves

are faster for two subjects (MS and EN);

the pairs of intercepts for both subjects

are significantly different according to

Z-scores (p < .03). But for three of the

subjects (CS, JD, and TB) the blinking

significantly retarded adaptation

during the initial stages. The intercepts

were significantly different for CS (p <

.0001) and JD (p < .0001); although the

intercepts were not significantly different for TB, the slope of the dark adaptation curve after blinking was

significantly slower (p < .0001).

Two of the subjects gave an explicit

reason. It was that the blinking main2
tained an afterimage of the light adapting screen and made it harder to detect

the test stimulus.

There is no relationship between the

ages of the subjects and the effects of the

blnking. Of the two whose adaptation

was slightly faster, one was 23 and the

other was 51; the three whose adaptation was retarded by the blinking were

31, 37, and 45.

There is, thus, little indication that

blinking facilitated the dark adaptation. In no case is the dark adaptation

curve associated with the blinking appreciably lower than the control curve,

and, of course, the blinking did not

produce complete dark adaptaion.

Stryker claimed that only about half the

individuals show a positive effect. But if

the positive effect is no greater than that

exhibited by the two subjects in this

study, it is not of practical significance

on submarines in view of the present

operational procedures.

Acknowledgment

I thank Dr. Christine Schlichting for

calculating the regression lines and Ms.

Kelly Johnson who collected most of the

data.

REFERENCES

H.D. Baker, Initial stages of dark and

light adaptation, J. Opt. Soc. Am.,

1963, 53, 98-103.

H.B. Barlow and H.J.M.B. Sparrock,

The role of afterimages in dark adaptation. Science, 1964, 144, 1309-1314.

G.S. Brindley, Two new properties of

foveal afterimages and a photochemical hypothesis to explain them. J.

Physiol., 1962, 164, 168-179.

J. Cohen and P. Cohen, Applied Multiple Regression/Correlation Analysis

for the Behavioral Sciences (2nd Ed.).

Hillsdale, N.J.: Lawrence Erlbaum,

1983, pp. 109-111.

R.F. Goad, COMSUBPAC letter of 7

June 1990 to Paul Weathersby.

W.A. Rushton, F.W. Campbell, W.A.

Hagins, and G.S. Brindley, The

bleaching and regeneration of rhodopsin in the living eye of the albino rabbit and of man. Optica Acta, 1955, 1

183-190.

V. Stryker, letter of 10 May 1990 to Executive Officer, Naval Submarine

Base, San Diego.

L.T. Troland, Preliminary note: The influence of changes of illumination

upon afterimages. Am. J. Psychol.,

1917, 28 497-503.

G. Wald. The photoreceptor process in

vision. In J. Field, H.W. Magoun, and

V.E. Hall (Eds.): Handbook of physiology, Vol. 1. Baltimore: Williams and

Wilkins, 1959.

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circles) or not blinking (open circles). The regression lines are least squares solutions. The subjects in

order of increasing age were KJ, MS, TR, VO, TB, JD, CS, RS, EN, SL.

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11. TITLE (Include Security Classification)

The effect of blinking on subsequent dark adaptation

12. PERSONAL AUTHOR(S)

S. M. Luria 13a. TYPE OF REPORT 13b. TIME COVERED 14. DATE OF REPORT (Year, Month, Day) 15. PAGE COUNT

Interim FROM _ TO 1991 May 14 6 16. SUPPLEMENTARY NOTATION

17. COSATI CODES 18. SUBJECT TERMS (Continue on reverse if necessary and identify by block number)

FIELD GROUP SUB-GROUP dark adaptation; blinking

19. ABSTRACT (Continue on reverse if necessary and identify by block number)

This study tested whether or not dark adaptation is facilitated by

blinking for a short time at the beginning of the dark adaptaion. The

course of dark adaptation was measured for 10 subjects both with and

without an initial period of blinking for 30 seconds. The blinking did

not improve the rate of dark adaptation.

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