REFERENCES

_ Brecher, G. A.: Optisch ausgeloste Augen- und
Korperreflexe am Kaninchen. Ztschr. f. verfl. Physiol.
23 :374, 1936.

. Brecher, M. H. and Brecher, G. A.
from visually induced disorientation in man.
mitted for publication)

Motor effects
(Sub-

3. Collewigh, H.: Changes in visual evoked responses

during the fast phase of optokinetic nystagmus in
the rabbit. Vision Res. 9 :803-814, 1969.

. Goetz, K. G.: Behavioral analysis of the fruitfly
drosophila. Proceedings of the symposium on infor-
mation processing in sight sensory systems sponsored
by the National Institute of Health and the California
Institute of Technology 85-99, 1-8 November 1965.

a

Moser, R.: Spatial disorientation as a factor in acci-
dents in an operational command, Aerospace Med.
40::174-176, February 1969.

. Nuttall, J. B.: The problem of spatial disorientation.

J. A, M. A, 166 :431-488, 1958.

. Nuttall, James B. and Sanford, William G.: Spatial

disorientation in operational flight in Medical Aspects
of Flight Safety, ed. Evrard, B., et. al, Pergamon
Press, 1959.

Pitts, D. E.: Visual illusions and aircraft accidents.
USAF School of Aerospace Med. Div. Brooks Air
Force Base, Texas. April 1967.





the second forward walk. The rest of the angles
formed by the nine walks were measured ac-
cording to the same procedure.

If the subject was disoriented, the second walk
across the drum would not have been in the same
path as the first walk across the drum. The
farther the subject had deviated from the first
walk with his second walk, the more his dis-
orientation and subsequent angle of deviation of
the first walk from the second walk would be.

For the control test all deviations of successive
paths of walking from one another were meas-
ured and these angles of deviations were given
absolute values. However, for the deviations
occurring while the optical environment of the
drum was moving, only those angles of deviation
which deviated in the same direction as the move-
ment of the drum were given positive values,
and the angles which indicated that a subject's
movement was in the opposite direction to the
movement of the drum were assigned negative
values.

Til. Results.

The average angle of deviation for the control
tests with a nonmoving drum was 3.1°
(S.D.+3.5). A regression equation for the tests
in the moving optical environment is shown in
Figure 1. The average angle of deviation for
each test was correlated with the speed of the
drum. The angle of deviation may be deter-
mined by the equation y’=.49x+8.69+11.1
standard error of estimate. In the above equa-
tion, y’ equals the predicted angle of deviation
for a test and x equals the speed of the optical
environment in rad./min. At faster speeds of
the optokinetic environment the subjects deviated
more than they did at slow speeds, though the
ratio of the predicted angle of deviation to the
speed of the drum decreased as the speed of the
drum increased. Only part of the decrease in
the ratio is explained by regression effects. One
may therefore state that the results indicate that
disorientation, as measured by the subject's

walking behavior, decreases relative to the
amount of increase in the speed of the visual
environment.

IV. Discussion.

At higher speeds of environmental stimulation
more rad./min. are required to induce a given
amount of disorientation, as measured by walk-
ing behavior. According to the subjective reports
from the participants in the tests, however, more
disorientation is experienced at higher speeds of
optokinetic stimulation. It is postulated here
that two factors may play a role in causing this
apparent contradiction. First, if a subject devi-
ates a great deal from a straight path of walking,
he is more likely to become aware of his devia-
tion through proprioceptor feedback and com-
pensate for this deviation after he has been told
to walk straight. Evidence for this is borne out
by the fact that some subjects report that they
feel they have deviated only when the drum is
moving faster than 20 rad./min., whereas at

‘slower speeds most of the subjects reported that

they thought they had walked straight when in
fact, they had not. Another factor to consider
with reference to this apparent discrepancy is
the increase in subjectively experienced disorien-
tation which is described to be similar to vesti-
bular effects with increases in angular accelera-
tion. Awareness of an increase in subjective lack
of knowledge of one’s objective location in space,
may cause the subject to compensate and thereby
counteract the influence of the environment on
his motor responses.

If it is true that a person is subjectively un-
aware of the disorientation he exhibits in a slow
moving optical environment, then caution must
be exhibited under such conditions. For flight
conditions in which no stable optical references
are available, pilots should become aware of their
potential disorientation and learn to identify cues
which would indicate that this type of disorien-
tation has occurred.


ANGLE OF DEVIATION

(DEGREES)
50)
y'=.49x+ 8.692 Ih
45 “| ys ANGLE oF DEVIATION
4 ( DEGREE)
-
al
40 x= SPEED OF DRUM
7 (RADIANS / MINUTE )
A
35
7
A ONE STANDARD ERROR — — —
30
7 i PREDICTED y

-
20 <4 4
| a1
An
15
}—~ 4
a
10
5
L-
5 10 18 20° 28 = 3085 0B

SPEED OF DRUM (RADIANS / MINUTE )

Fieure 1. Angle of deviation for a walking path in a rotating optokinetic drum in relation to the speed of the
drum. At higher speeds the degree of motoric disorientation becomes relatively less than the velocity increases:
of the moving optical environment.


AM 70-2

QUANTITATIVE EVALUATION OF OPTICALLY INDUCED
DISORIENTATION

M. Herbert Brecher, M.A.
Gerhard A. Brecher, M.D., Ph.D.
University of Oklahoma
Medical Center
Department of Physiology
And Biophysics
Oklahoma City, Oklahoma 73104

Approved by Released by

} Li Z § ; °
é
J. Roserr Drie, M.D. P. V. Srtcer, M.D.

Cuter, Crvit, AEROMEDICAL Feperat Amr Surceon
InstTITUTE

January 1970

Department of Transportation

FEDERAL AVIATION ADMINISTRATION
Office of Aviation Medicine





ACKNOWLEDGMENT

The authors are grateful to Mr. Frank Thurber for his technical
assistance.

Qualified requesters may obtain Aviation Medical Reports from Defense Documentation
Genter. The general public may purchase from Clearinghouse for Federal Scientific and
Technical Information, U.S. Dept. of Commerce, Springfield, Va. 22151.


QUANTITATIVE EVALUATION OF OPTICALLY INDUCED
DISORIENTATION

I. Introduction.

It has been established that man as well as
animals becomes disoriented in space when he is
exposed to a moving optical environment which
can be produced by a rotating optokinetic
drum'*. Recently the extent of such disorienta-
tion was measured by recording the motor reac-
tions of subjects who deviated from walking in
a straight path during optokinetic stimulation’.
The conclusion from these findings was that
under some flight conditions pilots could become
disoriented when the optical environment moves
and no cues from stationary optical targets are
available. Though most. flight accidents at-
tributed to “vertigo” are caused by labyrinthine
disorientation, some are probably caused by the
loss of stable optical reference points only**.
In that context, it has been implied that further
investigations of optogenic causes of accidents
are warranted’®. During a recent study of
altered motor activity in the optokinetic drum,
jt was established that the degree of disorienta-
tion increased with faster drum speeds’. In the
present paper, the association between the speed
of the drum and the extent of disorientation
was determined with a large number of subjects
at specifically selected speeds.

II. Methods.

A cylindrical drum was used in the experi-
ments for eliciting disorientation as previously
described?.

Thirty-four normal subjects were tested and
112 tests of subjects’ responses were made in the
moving optical drum. Thirty-four tests were
made in the nonmoving optical drum.

The subjects were tested at drum speeds rang-
ing from 3 rad./min, (radians/minute) to 45
rad./min. to observe the effects of the drum
speed on their walking behavior. Half the sub-
jects started the series of tests with the faster
speeds, whereas the other half started it with
the slower speeds.

A pen was taped to the subject’s left foot.
As the subject walked forward and backward
in the drum with a sliding motion, his path was
traced on a paper which had been placed under-
neath the drum for the subject to walk on.

Before entering the drum all subjects were
given the same instructions. First, they ‘were
told to slide their feet slowly using small steps
so that the pen remained constantly in contact
with the recording paper. When the subject
moved in this manner, a walk from one side of
the drum to the other took 6 (+2) seconds.
Secondly, the subjects were asked to hold their
heads with a small upward tilt so that they
looked upward and had no stationary visual
stimuli in view when the drum was moving.
Thirdly, the subjects were instructed to walk in
a straight line and to remain in the same path
while walking forward and backward in the
drum.

For each test, the subject was asked to walk
across the drum nine times. In each test the
subject walked forward five times and backward
four times (5 seconds of standing still were al-
lowed between walks). Before each series of
tests in the moving drum the subject was re-
quired to walk in the drum while it was not
moving. This test was used as a control measure
to determine the ability of the subject to walk
straight when he was not under the influence of
the stimulation from the spinning drum.

The amount of disorientation of the subject
was obtained by measuring the angle formed by
two successive walks. The first angle in a test,
for example, would be formed by a forward
walk and a successive backward walk. Three
points formed this angle. First, the point at
which the subject began walking forward;
second, the point at which he stopped walking
forward, which was also the point at which he
began walking backward; third, the point at
which he stopped walking backward. The next
angle is formed by the first backward walk and