29.
28
27
26
25
24
23
22
2!
20
19
18
\7
16
5
14
13
12.
in

FUSION TIME
(SEC)

o-nu tf ann @

CONTROLS ——
SLEEP-DEPRIVED-----~

DAY

Ficure 2. Graphs of Fusion Times of Each Subject.

Table 2 is composed of ratios of the fusion
times on the morning of each day to the after-
noon of each day. Sixty percent of the controls
and 79 percent of the sleep-deprived subjects had
faster fusion times in the afternoons than in the
mornings.

Table 3 is similar to Table 2, except that the
ratios were obtained by dividing each afternoon’s
fusion time by the fusion time measured the next
morning. Seventy percent of the controls’ values
on next morning were less than the values on
the previous afternoon. Tables 2 and 3, taken





120

110

3
.3)
|

CONTROLS °
SLEEP-DEPRIVED @

804

70

AVERAGE FUSION TIME
% OF FIRST DAY'S TIME

604

50

40

AM PM | AM’ PM] AM’ PM | AM!’ PM | AM! PM |
t 2 3 4 5

DAY

Fieure 1. Graph of Average Fusion Times of the Two Groups in Percent of Initial Value for Hach Period.

four of the control subjects showed improved
fusion times. Figure 1 is a graph of average
fusion times of the two groups expressed in
percent of the initial value for each observational
period. The image displacement represented by
this graph is two squares to the left, so chosen
because it represented a fusional task of inter-
mediate difficulty that was accomplished by all
of the subjects except for one control subject
(No. 8). It shows steady improvement of fu-
sional ability by both groups over the five-day
period with the sleep-deprived group out-per-
forming the control group. Both groups finished
the experiment with average fusion times below
the initial value.

Figure 2 is a group of graphs representing
the average fusion times of each subject for two
squares to the left for each observational period.
No differentiation between the groups is sug-

gested. The one control subject (solid lines)
with such high and erratic values must not be
considered as significant. That subject was er-
ratic in the other experiments, also, and exhibited
a great deal of anxiety and general confusion
‘with inappropriate responses in conversation and
concern for himself as an experimental subject.

The rationale was adopted that, if fatigue in-
duced by sleeplessness caused an increase in fusion
time, the fusion time at the end of the experiment
should be the longest. Table 1 is made up of the
ratios of the initial fusion times to the fusion times
at the end of 86 hours. Thus, values in the table
that are greater than unity indicate that the termi-
nal fusion time was less than the initial. All of the
group averages are greater than unity. Because
of the fact that some of the fusion times are
infinite (no fusion), statistical treatment of the
values is not feasible.


together, indicate that fusion time progressively
speeded up over the 86-hour period in both con-
trol and sleep-deprived groups.

One observation made at the time of the fusion
time determinations is not reflected in the data
and must be prefaced with the following expla-
nation. The apparatus used in this study allows

Tanre I—Fusion Time First Day/Fusion Time Last Day

SLEEP DEPRIVED

Squares Displacement
Left

Squares Displacement

Subject
No. 1 2 3 1 2 3
1 11 43 14 0.6 0.6 5.7/NF*
2 12 14 16 12 0.4 04
3 8.0 8.8 ved 45 o1 12.8
4 0.4 0.4 0.2 16 2.4 13
5 0.7 14 12 10 1.0 15
6 0.8 2.9 2.0 0.7 NF/NF NF/NF
AY. 2.0 3.0 13 16 27 4.0

CONTROLS,

7 18 25 44 3.2 15 NF/65
8 0.6 0.6 NF/NF 0.2 NF/NF NF/NF
9 13 0.9 07 15, 11 13
10 3.0 16 7 14 NF/NF_ 64/NF
n 1.0 14 07 18 L7 0.9
2 1.0 2.2 21 13 12 NF/LB8
Ay. 15 15, 19 16 14 11

*NF=No Fusion.

Taste II,—Fusion Time Each A.M./Fusion Time
Each P.M.

(2nd Square Left Only)
SLEEP DEPRIVED

Day*
Sudject

No. 2 3 4 5
1 13 12 19 19

2 ww 12 12 12
3 3.0 12 07 14

4 13 0.7 10 0.2

5 16 0.8 1.0 0.9

6 16 a1 7 2.9
Ay. LT 1.0 138 14

CONTROLS

7 05 13 12 11
Bee _ _ _ _
9 a OT 07 0.9
10 12 16 05 1.0
1 54 14 wa 0.9
12 0.5 18 12 08
Ay. Lz 14 0.9 0.9

*First day omitted because schedule did not permit
a P.M. determination.

**Subject failed to accomplish fusion.

Tasxe III.—Fusion Time P.M. Hach Day/
Fusion Time A.M. Next Day

(2nd Square Left Only)
SLEEP DEPRIVED
P.M. Day/A.M, Day

Subject

No. 2/3 3/4 4/5
1 21 0.4 0.8

2 0.8 0.9 0.9

3 0.8 2.0 11

4 10 14 10

5 15 11 08

6 1.0 0.6 04
Av. 12 li 08

CONTROLS

7 14 0.6 12
gee --- a a+

9 15 10 16
10 04 15 13
lt 0.8 08 11
12 11 10 10
Av. 10 10 12

*Ratio for Day 1/Day 2 omitted because schedule did
not permit a P.M. determination on Day 1.

**Subject failed to accomplish fusion.

an image to be placed anywhere on the retina
of the right eye and does not cause any axis
deviation, That is to say, the subjects’ resting
phoria was present throughout the experiment.
That heterophoria apparently varied slightly
from time to time, necessitating a readjustment
of the Risley prisms to position the light source
at the desired place on the grid. When the sub-
ject first sat down, a “try and see” method of
adjustment was used to arrive at the desired
image placement. In the fatigued subjects
toward the end of the experiment, the image
became extremely difficult to set. The experi-
menter would think that the light was properly
positioned only to have the subject report upon
beginning the determination that the light had
moved or that it had disappeared entirely. Upon
several occasions the subjects’ heterophoria be-
came so variable that attempts to obtain a
stabilized image placement had to be abandoned.

IV. Discussion.

The lack of effect of sleeplessness on the bin-
ocular fusion reflex should not be taken to mean
that the sleep-deprived subjects in this experi-
ment were not fatigued. At times toward the
end of the sleepless period, some of the subjects
hallucinated. One tried to pick up the painted


AM 69-1

BINOCULAR FUSION TIME IN SLEEP-DEPRIVED
SUBJECTS

C. E. Melton, Ph.D.
Marlene Wicks

Approved by Released by
J. Rosperr Ditie, M.D. P. V. Srecet, M.D.
Cuter, Crvin AEROMEDICAL Feperat Arr SurGEON
Instirure

January 1969

Department of Transportation

FEDERAL AVIATION ADMINISTRATION
Office of Aviation Medicine



parking space lines in a parking lot; another
made an elaborate detour around an imagined
roll of barbed wire on the sidewalk. In all
probability, three factors operated to contribute
to lack of measureable effect; (1) the resistance
of the reflex to fatigue and (2) the ability of the
subjects to “muster their reserves” for the brief
period of the determination. A third factor,
obviously, is that when a subject became so er-
ratic that the target could not be set, no measure-
ments were made and no data were acquired.

Brecher, et al.‘ also found heterophoria to
change during fatigue. These workers, however,
reported that the binocular fusion reflex failed
after about 30 hours of sleeplessness. They
further reported that the fusion reflex failed
first at an observation distance of 33 cm, then
at 82 cm and last at 6 meters, indicating that the
reflex was more difficult to maintain when more
convergence was called for.

The slowed binocular fusion technique has
been compared with an objective cinematographic
technique and it was claimed that good correla-
tion existed’. However, neither method meas-

ured “natural” fusion time which would apply
when a person regarded a scene containing ob-
jects at different distances. Therefore, conclu-
sions drawn from the results of this study
regarding the ability of extremely fatigued sub-
jects to accomplish or maintain fusion under
natural conditions must be made with caution.
The slowed binocular fusion time method is
merely one test for the strength of a reflex under
one set of conditions. It is a particularly useful
method when a series of measurements are to be
made on the same person, thus showing a trend
if such is present.

Such a trend was apparently shown by both
groups, in the direction of improvement of rate
of binocular fusion. This result could have been
caused by the orthoptic training inherent in the
procedure or by some more subtle learning
process. Suffice it to say, however, that fatigue
did not prevent the improvement. This finding
is consistent with the results of the other study
that was concurrently executed, that the regula-
tion of body temperature and the excretion of
catecholamines, magnesium and creatinine were
unaffected significantly by sleep deprivation.

REFERENCES

1. Beyyerr, A, G., Wetts, A. H., Bryper, R. T. anp
Brecuer, G. A. “Subjective and Objective Criteria
of Binocular Fusion” Am. J. Optom. and Arch. Am.
Acad. Optom. Monograph 221, 1958.

2. Brecuer, G. A. “Quantitative Studies of Binocular
Fusion.” Am. J. Ophthal. 38: 134-141, 1954.

3. Brecuer, G. A., Harrman, A. P., ano Leonarp, D. D.
“Effect of Alcohol on Binocular Fusion.” Am. J.
Ophthal. 89 : 44-52, 1955.

4, Brecuer, G. A., Purnett, BE, W., anp Hoover, W. J.
“The Influence of Depressants, Fatigue and Stim-

ulants on Binocular Fusion.” 4th. Invitational Con-

ference for Visual Research Specialists, Sponsored
by Lamp Division, General Electric Co., Nela Park,
Cleveland, Ohio, April 23-25, 1956.

Frorrca, V., Hiectns, EB, A., amprmrro, P. F., Lave-

cota, M. T., anp Davis, A. W. “Physiological Re-
sponses of Men During Sleep Deprivation.” J. Appl.

Physiol. 24: 167-176, 1968.

. Metron, C. E, anp Wicks, M. “Pilot Vision Con-
siderations: The Effect of Age on Binocular Fusion
Time.” OAM Report No. AM 66-35, October 1966,

a

2



Acknowledgment

The authors are grateful to Mr. J. T. Saldivar for the preparation of
the figures.

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,


BINOCULAR FUSION TIME IN SLEEP-DEPRIVED SUBJECTS

I, Introduction.

The time required for the attainment of bin-
ocular single vision when the gaze is changed
from one distance to another is a component of
total reaction time and may be critical at the
closing speed of modern aircraft on collision
courses. When diplopia is prismatically induced
binocular fusion time is reported to be increased
by alcohol ingestion’, drugs and fatigue‘, and
age’. This report deals with binocular fusion
time in six subjects fatigued by 86 hours of sleep
deprivation.

IL. Methods.

Six pairs of paid subjects, all less than 30
years of age and with good binocular vision,
were studied; one subject in each pair was kept
awake continuously for 86 hours while the other
subject maintained a normal sleep/wakefulness
regime and served as a control. Measurements
of binocular fusion time were made each morning
and evening throughout the experimental period.
The subjects were allowed food, water, soft
drinks, tobacco and de-caffeinated coffee ad
libitum. Wakefulness was assured by a 24-hour
watch maintained by project investigators. Rec-
reational facilities (pool table, pin ball machines,
painting equipment, TV, etc.) were available for
the exclusive use of the subjects to aid in main-
taining wakefulness. Control subjects were
treated the same as sleep-deprived subjects except
that they were allowed to sleep through each
night in the CAMI clinic.

Briefly stated, the procedure for determining
binocular fusion time was modified from that
originally described by Brecher*, and involved
the presentation of a light steadily to the left
eye and interruptedly to the right eye. The light
source was situated in the center of a blackboard
that was marked off into five cm squares, Inter-
rupted presentation of the light was accomplished
by a cylindrical shutter rotating at 2.5 rps.
Crossed Risley rotary prisms positioned in front

of the shutter allowed the image in the right
eye to be positioned as desired. Measurements
were made at six image positions, one, two, and
three squares left and right. Any hyper- or
hypophoria was eliminated by appropriate pris-
matic adjustment and all measurements were
made with the subjects’ eyes located six meters
from the light source. Under these conditions,
the prismatically-induced diplopia initiated a
reflex attempt to fuse the two images. The inter-
rupted presentation of the target slowed the
fusional process so that it could be accurately
measured. The subject controlled the process by
means of a single button that, when pressed,
opened an occluder shutter positioned between
his eye and the constantly running cylindrical
shutter and simultaneously started an electric
timer. When he perceived one image, he simply
released the button, thus closing the occluder
and stopping the clock. The details of the
method have been previously published*,

Some learning is involved on the part of the
subject in the operation of the apparatus and
in perception of the fusional process. Thus, on
the morning of the first day the subjects were
tested until their fusion times became consistent
and they could easily detect the extent and di-
rection of image displacement. Their initial
binocular fusion times were then determined.
It is probable that some learning continued
throughout the five-day period. Since this study
was secondary to a larger study it was not pos-
sible to have the subjects in the laboratory long
enough to be assured that they were on the final
plateau of their learning curves.

III. Results.

Sleep deprivation had no pronounced effect on
the binocular fusion reflex as far as fusion time
was concerned (Fig. 1, Tables 1-3). Five of the
sleep-deprived subjects showed shorter fusion
times at the end of the 86-hour sleepless period
than at the beginning of the experiment and