AM 67-24 

REACTION TIME AS A FUNCTION OF FLASH 

LUMINANCE AND DURATION 

Approved by 

~~ J. ROBERT DILLE, M.D. 

CHIEF, CIVIL AEROMEDICAL 

INSTITUTE 

Mark F. Lewis, Ph.D. 

and 

Henry W. Mertens 

November 1967 

Released by 

~AM) P. v. SIEGEL, M.D. 

FEDERAL Am SuRGEON 

FEDERAL AVIATION ADMINISTRATION 

Office of Aviation Medicine 
ACKNOWLEDGMENTS 

The authors would like to thank Faye K. Ashby who assisted in the 

collection of data, and Becky Johnson and Ronald Morris who served as 

patierrt subjects. 

Qualified requesters may obtain Aviation Medical Reports from Defense Documentation 

Center. The general public may purchase from Clearinghouse for Federal Scientific 

and Technical Information, U.S. Dept. of Commerce, Springfield, Va. 22151 
REACTION TIME AS A FUNCTION OF FLASH LUMINANCE 

AND DURATION 

I. The Problem 

Because of the high speed of modern aircraft, 

pilots must respond quickly to signal lights from 

the ground or other aircraft during night flight. 

The present study was concerned with the relation of reaction time to flash luminance and 

duration. The study was directed at the limiting case where the operator knows the position 

in space where the flash appears and where the 

behavior required of the operator is very simple. 

The relation between simple reaction time and 

the effects of stimulus luminance and duration 

has been inadequately investigated. Only a few 

studies have been concerned with the effect of 

stimulus duration on simple reaction time. 

Froeberg1 used stimuli of 3, 6, 12, 24, and 48 

msec and obtained an inverse relation between 

reaction time and stimulus duration. Wells2 

used stimuli of 12, 25, 64, 144, and 1000 msec at 

a luminance below 0.5 mL and reports fastest 

reaction times for the 25- and 64-msec flashes, 

with slower reaction times for stimuli that were 

either shorter or longer than these optima. 

Baumgardt & SegaP investigated reaction time 

to stimuli of 50 and 250 msec at a luminance of 

1700 nits ( 534 mL), with the two durations 

presented in alternating blocks of ten trials each. 

Comparisons between the means for successive 

blocks showed faster reaction times for the 50-

msec stimulus. 

Raab, Fehrer, & Hershenson4 have criticized 

the above studies on several grounds. They 

point out that the reaction times obtained by 

Baumgardt & SegaP to the 250-msec flash were 

in every case shorter than the stimulus, a circumstance that obscures the relation, since reaction time could not be influenced by that part 

of the flash which followed the occurrence of 

the response. 

Referring to Johnson's rationale5 for reaction 

time experiments and J arl's demonstration6 that 

the presentation of stimuli in homogeneous 

1 

blocks yielded effects not obtained when all 

stimuli were presented in random order within 

a session, Raab, Fehrer, & Hershenson4 also 

criticized both the W ells2 and the Baumgardt & 

Segal studies for presenting the stimuli in blocks 

of trials at the same duration; thus, they attribute the results at least in part to the method 

of stimulus programming. 

Raab et aU replicated the Baumgardt & Segal 

experiment and, at a higher luminance level, 

achieved the same result. They also obtained 

reaction times to stimuli of 10, 25, 50, 100, 250, 

and 500 msec at luminances of 0.30, 30, and 3000 

ft-L. In the latter experiment, durations were 

randomized within sessions at single luminance 

levels, but with luminances counterbalanced over 

sessions. Although reaction time was found to 

be inversely related to luminance, no effect due 

to duration was obtained. 

In a later study, Raab & Fehrer7 obtained reaction times to stimuli of 0.5, 1, 2, 5, 10, and 20 

msec at luminances of 0.3, 3, 30, 300, and 3000 

ft-L. Again, durations were randomized within 

sessions at a single luminance and luminances 

were counterbalanced across sessions. For the 

two highest luminances, duration had no effect 

on reaction time. For the 3 and 30 ft-L flashes, 

reaction time increased over the range from 5 

to 0.5 msec duration. At 0.3 ft-L, reaction time 

was inversely related to duration over the entire 

range investigated. At all durations, reaction 

time increased as luminance decreased. From 

these data, Raab & Fehrer concluded that the 

critical duration for reaction time (defined as the 

flash duration beyond which prolongation of the 

stimulus has no effect on reaction time) is less 

than 0.5 msec for luminances greater than 300 

ft-L, and increases with decreasing luminance 

to about 10 to 20 msec at a luminance of 0.3 ft-L. 

Use of the term "critical duration" by Raab 

& Fehrer7 was criticized by Lewis8 because Raab 

& Fehrer failed to show agreement with Bloch's 

law for constant reaction time criteria. Lewis 
also suggested that both luminance and duration 

should be randomized within sessions. In Lewis' 

experiment a stimulus of 8-msec duration was 

matched in luminance (10 mL) to one stimulus 

of 2-msec duration, and matched in energy to 

another stimulus of 2-msec duration (40 mL). 

The obtained reaction time distributions indicated that stimuli of equal energy but unequal 

duration yield equivalent reaction time distributions, a finding at variance with the data of 

Raab & Fehrer. 7 Lewis concluded that for constant reaction time distributions, Bloch's law is 

valid. 

The current experiment attempted to extend 

Lewis' finding to a greater range of luminances 

and durations. 

II. Method 

Subjects. The subjects were a man and woman 

undergraduate at the University of Oklahoma. 

Both were emmetropes. Both were screened for 

color vision deficiency on a battery including 

the A.O.-H.R.R. and Dvorine Plates, the Farnsworth-Munsell100 hue test, and an anomaloscope 

examination. No evidence of color deficiency 

was found. Both were paid an hourly wage. 

Apparatus. A Maxwellian view optical system, previously described,9 was designed to deliver a 0.5° stimulus to the fovea. Fixation was 

assisted by four broken red lines in the form of 

a cross around the test spot. Equipment for 

generating flashes and for control of flash luminance and duration >vere identical with the equipment used in a previous study ;

9 the same calibration procedure was used as before. Reaction 

time was measured from flash onset to release 

of a microswitch requiring 110 grams of force 

for depression. Reaction times were recorded 

from a Hewlett-Packard Model 523CR Electronic Counter. 

Procedure. Experimental sessions began with 

a seven minute period of dark adaptation following which the subject adjusted the intensity 

of the fixation lines until they were just visible. 

The following instructions were then read to the 

subject: 

"vVhen you hear the ready signal, sight 

through the tube and fix your gaze on the center 

of the cross. "\Vhen ready, press and hold down 

the switch. You will hear a noise for a period 

during which a flash will appear in the center 

2 

of the cross. As soon as you see the flash, release the switch as quickly as possible. On some 

trials no flash will appear. Release the switch 

only when you see a flash. Do you have any 

questions~" 

If there were no questions, the experimental 

session was begun. The experimenter initiated 

each trial by giving the subject a ready signal 

consisting of a short 1000 Hz tone. When prepared, the subject pressed the switch which delivered white noise to his earphone. The stimulus was then presented after a foreperiod which 

varied from 1 to 3 seconds, in steps of 0.5 second, 

and which was randomly assigned to the trial. 

The white noise was terminated when the subject 

responded to the stimulus by releasing the switch. 

Each trial was followed by a 20 second intertrial 

interval. 

The 86 stimuli ranged in luminance from 7.9 

to 15,850 mL and in dura:tion from 2 to 1024 

msec. These stimuli and nine blank trials were 

presented once in each of two random series used 

in an experimental session. The blank trials 

differed only in that no visual stimuli were presented. No responses were obtained on blank 

trials. 

At the beginning of each experimental session, 

10 practice trials were given. The stimuli for 

practice trials always had a luminance of 7943 

mL and a duration of 512 msec. Foreperiod 

duration was varied as in experimental trials. 

Both subjects were given six practice sessions 

before data collection began. The subjects, RM 

and BJ, were given 24 and 26 experimental sessions, respectively, and there were corresponding 

numbers of 48 and 52 reaction times obtained 

for each stimulus. After the practice sessions, 

the time required for each daily experimental 

session was approximately 1.5 hours. 

III. Results and Discussion 

The median reaction time was determined 

from the distribution of reaction times (see appendix) for each stimulus. For each subject 

median reaction time is shown as a function of 

luminance with flash duration as a parameter 

in Figure 1. Although there are several prominent reversals, the reversals do not appear to be 

systematic. Reaction time appears to be a decreasing, negatively accelerated function of flash 
luminance. It is not clear that there is any effect 

due to flash duration. 

210 

o 2m-

• 4 •II 

270 • 8 •II 

• 18 

a 32 •• • 84 •• • 128 

•258 

0 512 

• 1024 

200 

.9 1.5 2.1 2.7 3.3 3.9 .9 1.5 2.1 2.7 3.3 3.9 

Loo L lmll 

FIGURE 1. Median reaction time as a function of log 

luminance with flash duration as a parameter. 

For clarity, some functions have been shifted along 

the ordinate by an amount shown to the left of the 

function. Data for subject RM are on the left; 

for subject BJ, on the right. 

In Figure 2 the same data are plotted as a 

function of flash duration with flash luminance 

as a parameter. 

Although there is considerable noise in the data, 

reaction time does not appear to be systematically 

influenced by flash duration at any of the luminance levels examined. 

Because of the apparent lack of stimulus duration effects on the reaction times obtained, the 

data have been averaged across durations to 

clarify the luminance effect (Figure 3). 

Figure 3 shows that reaction time is a negatively 

accelerated function of flash luminance for both 

subjects. 

The results of the current study support the 

findings of Raab, Fehrer, Hershenson4 and of 

Raab & Fehrer' that reaction time is independent 

of flash duration at high luminances over the 

range of durations investigated. The current 

3 

210 

"" 

240 

200 

o•.al .... L .s.s 

&S.I 

•s.s 

•s.o 

•2.7 

02.4 

0 '·' • I.S 

• 1.2 * 0.1 

-~ 

B. J • 

2 • o•n~•m~-• •, ·~-~~~~ 

Tllllttcl 

FIGURE 2. Median reaction time as a function of flash 

duration with flash luminance as a parameter. 

Data for subject RM are on the left; for subject 

BJ, on the right. 

i 

E 

"' 

~ ... 

z 

0 

;:: 

u 

<( 

"' 0: 

260 

250 

240 

230 

220 

210 

200 

.9 1.2 1.5 1.8 2.1 2.4 2.7 3.0 3.3 3.6 3.9 4.2 

Loo L lmLI 

B.J. 

FIGURE 3. Median reaction time as a function of log 

luminance. Data are averaged across durations 

shown in Figure 1. Data for subject RM are on 

the left; for subject BJ, on the right. 

study fails, however, to replicate the effect of 

duration obtained at lower luminances by Raab 

& Fehrer7 and by Lewis.8 Additionally, examination of the reaction time distributions obtained 

in the current study casts doubt on the validity 

of Lewis' earlier conclusion8 that Bloch's law 

holds for constant reaction time distributions. 

The data support the suggestion (implicit in 

Raab & Fehrer's discussion7 and explicitly stated 
by Kahneman10 ) that it is incorrect to speak of 

the critical duration for Bloch's law without 

stating the criterion response, i.e., Bloch's law 

holds for a constant response criterion up to 

some critical duration. The critical dura:tion is 

not, however, independent of the response criterion. The current data, together with those 

of Raab, Fehrer, & Hershenson4 and Raab & 

Fehrer7 , suggest that for reaction time criteria 

the critical duration, if it exists, is extremely 

short. It must be noted that in the absence of 

a demonstration that Bloch's law holds for reaction time criteria, the "critical duration" discussed above is not necessarily the critical duration of Bloch's law. Rather, it is the duration 

at which reaction time becomes independent of 

stimulus duration and this need not be identical 

w~th the duration at which the integration of 

energy for a constant reaction time criterion 

ceases. 

REFERENCES 

1. FROEBERG, S.: The relation between the magnitude 

of stimulus and time of reaction. Arch. PsychoZ., 

8:1907. 

2. WELLS, G. R.: The influence of stimulus duration 

on reaction time. PsychoZ. Monogr., 15:5 (whole 

No. 66), 1913. 

3. BAUMGARDT, E. and SEGAL, J.; Facilitation et inhibition parametres de la fonction visuelle. Annee 

PsychoZ., 48:54-102, 1942. 

4. RAAB, D. H., FEHRER, E., and HERSHENSON, M.: 

Visual reaction time and the Broca-Sulzer phenomenon. J. exp. Psychol., 61 :193-199, 1961. 

5. JoHNsoN, H. M.: Reaction-time measurements. 

PsychoZ. BuU., 20 :562-589, 1923. 

6. JABL, V. C.: Method of stimulus presentation as 

4 

antecedent variable in reaction time experiments. 

Acta PsychoZ., 18 :225-241, 1957. 

7. RAAB, D. H., and FEHRER, E. : Supplement&ry report: The effect of stimulus duration and luminance on visual reaction time. J. exp. PsychoZ., 

64 :326-327, 1962. 

8. LEwis, M. F. : Magnitude es.timation and reaction 

time as functions of flash luminance and duration 

in the fovea. Unpublished Ph.D. dissertation, Columbia University, 1964. 

9. LEWis, M. F.: Cross-modality matching of loudness 

to brightness for flashes of varying luminance and 

duration. OAM Report AM 67-16, May, 1967 (in 

press). 

10. KAHNEMAN, D.: Time-intensity reciprocity in acuity 

as a function of luminance and figure-ground contrast. Vision Research, 6:207-215, 1966. 
APPENDIX 

Distributions of reaction times in response to onset of visual stimulus. Points shown in each figure 

are the interpolated deciles of each distribution. Distributions for single durations are presented 

in each figure. Data for each subject are presented separately. 

·~c~----~~~~~-"" 

.8 

.7 

.. 

. o 

.4 

.3 

.2 

o 4.2 Lot rnL 

• 3.9 

130 140 150 160 170 180 190 

T(msed 

1.0 

.9 

.. 

.7 

. 

.5 

.4 

.3 

.2 

o 4.2 Lot mL 

• 3.9 

A 3.6 

.. 3.'3 

0 3.0 

• 2.7 

• 2.4 

• 2.1 

.1~~--~~--L--L--~~--~~--

B. J . 

t•Smsec 

150 160 170 180 190 200 210 220 230 240 250 260 270 280 290 300 

T (msec) 

FIGURE lA 

FIGURE SA 

1.0 1.0 

. 9 .9 

. 8 B. J . .8 

.7 t •4msec .7 

.6 .6 

.5 .5 

.4 .4 

.3 .3 0 3.9 Lot rnL 

0 4.2 Lot "'l . ... • 3.9 . ... . ... . 3.0 

.2 • 5.3 .2 0 2.7 0 3.0 . 2.4 • 2.7 . 2.1 

. 1.0 

~~~~~====~=~=~~~ ~~~~oo=w=~ 

T {msed T Cm•c) 

FIGURE 2A FIGURE 4A 

Appendix 5 

B.J . 

1•16 msec 
1.0 

.9 

. 8 

.T 

.6 

. 5 

.4 

·' 

.2 

o 3.6 L09 ml 

• 3.3 

A 3.0 

• 2.'1 

• 1.8 

• 1.5 

B. J. 

t•32msee 

1.0 

.9 

.. 

.6 

.. 

.4 

·' 

.2 

0 3.6 LOO lfll 

• 3.3 

[J 2.4 

• 2.1 

... 0 1.2 

• 

B. J. 

t •256 msec 

.II~50:--:1::60:--:I:=To=-~~e-=-o-::190':--::200=:--:2~10:--:2=20:-2:::'l0':--::-240':--:::::-:~~=-="':-::~~-==:-=-~ 

T lmsec:l 

·',e":o:-:190:'::---:200:'::--,2:'clo:-2:':20=-:2:':l0:-c2:-'4::-0-2:-'50::---=:"-'0'0:-~=-:2~90:-::,~oo:-:,="lo"-:3"c20:-:,o:,-:-o--cl4~o-,=so~:-'l60 

T lmst<:l 

1-

1.0 

.9 

.8 

.T 

.6 

.5 

.4 

0 3.6 Lo9 mL 

• 3.3 

FIGURE 5A 

~ .3 

.. 2.7 

.2 1.8 

0 I .2 

150 160 170 180 190 200 210 220 230 240 

T (msed 

B. J. 

t•64 msec 

1.0 

. 9 

.8 

.T 

.6 

.5 

.4 

·' 

.2 

o 3.!> Loo mL 

., 

<lo 3.0 

.. 2.7 

0 2.4 

• 1.~ 

0 1-2 

• 0.9 

FIGURE SA 

FIGURE 6A FIGURE 9A 

1.0 

.9 

.8 1.0 

• T .. 

.8 .. 

.. . .. .. . 3 0 3.6 L ... IIIL 

·' . ... &2.7 

. 2 0 ... .2 

. ... 0 1.2 

140 150 160 170 180 190 200 210 220 230 240 250 260 270 280 290 300 310 140 150 160 170 180 190 200 210 220 

T (msed T lmnc I 

FIGURE 7A FIGURE lOA 

Appendix 6 

B. J • 

t• 512 msec 

8. J . 

t•I024 mnc: 
... 

1.0 

.9 

.8 

.7 

.6 

.5 

.4 

R. M. 

0 4.2 L .. .._ 

. 3.9 

3.6 

3.3 

0 3.0 

. 2.7 

~ .3 

.2 

.I C-~--~~--~--L--L--~~~~~~---L--~~--~~ 

150 160 170 180 190 200 210 220 230 240 250 260 270 280 290' 300 

1.0 

. 9 

.8 

.7 

.6 

.5 

.4 

.3 

1.0 

.9 

. 8 

.7 

.6 

.5 

.4 

.3 

.2 

T (ms•c) 

FIGURE llA 

R.M . 

1•4 msec 

T (msecl 

FIGURE 12A 

o 4.2 Lot mL. 

• 3.9 

t:. 3.6 

3.3 

3.0 

• Z.7 

a 2.4 

o 4.2 LoQ mL 

• 3.9 

150 160 170 180 190 200 210 220 230 240 250 260 270 260 290 300 

T{msecl 

FIGURE 13A 

Appendix 

1.0 

.9 

.8 

.7 

.6 

.5 

.4 

R.M. 

t•l6 msec 

~~~~~~~~-=--==-~= T (msecl 

1.0 

.9 

.8 

. 7 

.6 

.4 

.2 

FIGURE 14A 

0 3.6 Lot ML 

• 5.3 

.6 3.0 

• 2.7 

a 2.4 

• 2.1 

• 1.8 

• 1.& 

140 150 160 170 180 190 200 

1.0 

.. 

. 8 

.1 

.6 

·" 

.4 

;:: 

~.3 

!0 

.2 

0 3.6 l.o9111L 

• 3.3 

A 3.0 

.. 2.4 

0 2.7 

• 2.1 

• 1.8 

• 1.~ 

0 1.2 

T (msec) 

FIGURE 15A 

R. M • 

t•32 msec 

R.M . 

t•64 msec 

140 1!)0 160 170 180 I~ ZOO 210 ZZO Z:30 Z40 ZOO 260 Z70 280 Z90 300 

T (msecl 

FIGURE 16A 
1.0 . 9 ~ .8 

. 7 

.6 

.5 

.4 

.3 3.6 LOQ mL 

• 3.3 

\'~ 

R. M. 

t•I2Bmsec 

.2~~~~·~ 140 150 160 170 180 190 200 210 '~~ 220 230 240 250 260 270 280 290 300 

1.0 

.. 

.8 

.7 

.6 

.5 

.. 

. 3 

.2 

0 3.6 Lot mL 

• 3.3 

.. 2.7 

D 2.4 

• 2.1 

• I .2 

0 1.5 

• o .• 

T {msecl 

FIGURE 17A 

R.M. 

t• 256 msec 

140 150 160 170 180 00 200 210 220 230 240 ~ 260 270 280 290 500 

T (msecl 

FIGURE 18A 

Appendix 

... 

~ 

!!0 

.. 

8 

1.0 

.. 

.8 

.7 

.6 

.5 

.4 

.3 

.2 

0 3.6 Lot mL 

• 3.3 

~ 3.0 

<> 1.2 

• 0.9 

140 150 160 170 180 190 200 

T {msed 

FIGURE 19A 

1.0 

.. 

.8 

.7 

.6 

.5 

.. 0 3.6 Lot 1111.. 

.3 . 3.3 

. 3.0 

D . .. .2 . 2.1 

. ... . ' .. 0 0.2 

• 0.0 

R.M . 

t•512 msec 

R. M. 

t•l024 msec 

140 150 160 170 180 190 200 210 220 230 240 250 260 270 280 290 300 

T lmsecl 

FIGURE 20A 

3930