Before entering the drum all subjects were
determined to have normal vision and given the
same instructions. First, they were told to slide
their feet slowly, using small steps so that the
pen remained in continuous contact with the re-
cording paper. A walk from one side of the
cylinder to the other took 6-+2 seconds when the
subject moved in this manner. Secondly, the
subjects were instructed only to look up to ex-
clude peripheral vision of the floor and to try to
watch a particular horizontal line which went
completely around the upper area of the inside
of the drum. Thirdly, the subjects were asked
to walk in an absolutely straight line and they
were told to try to remain exactly in the same
straight path as they walked back and forth.

On each test the subject was asked to walk
first forward and then backward till he had com-
pleted a total of nine walks. Five seconds were
allowed between walks. After the ninth walk
the subject was asked to step out of the drum.
While the subject stayed outside, the recording
paper was replaced and the drum speed altered
as required by the test.

Before the beginning of each series of tests
with the moving cylinder, the subject was re-
quested to walk back and forth in a straight
line in the stationary drum. The pattern of this
walk was used as a control.

The degree of disorientation of the subject was
obtained by measuring the angle formed by two
successive walks, one forwards the other back-
wards (Fig. 2). If the subject is not disoriented
this angle will be negligible or even unmeasur-
able. If the subject is disoriented, the second
walk will not be in the same path as the first
and the farther the subject has deviated from the
first walk the more his disorientation and subse-
quent angle of deviation will be. For the control
walk all deviations of successive paths were
measured and the angles of deviation were given
in absolute values. For the deviations occurring
while the optical environment of the drum was
moving, only those angles of deviation which
pointed in the same direction as the movement
of the drum were assigned positive values and
the angles in the opposite direction of the drum’s
turning were represented as negative values.

The subjects were exposed to speeds ranging
from 3 to 45 radians per minute and their angles
of deviation were measured. During the tests the

experimenter gave instructions from the same.

Cc A

Fieure 2. Typical walk pattern in a moving optical
environment, clockwise at 3.1 to 9.0 radians/min.
‘The solid line from A to B represents the first for-
ward walk. The solid line from B to C represents
the first backward walk. The angle between the
broken lines is the first angle of deviation from a
straight walk.





orientation, as measured by the angle of deviation
from the control, and the speed of the drum.
When the tests were divided into seven groups
on the basis of the speeds of the drum the analysis
of variance test revealed a significant (F=2.4995,

B

c A

Ficure 4, Walk pattern in an optical environment mov-
ing from 21.1 to 27.0 radians/min. (see Fig. 2).

p<0.05) positive interaction between the degree
of disorientation and the speed of the total optical
environment.

The walking patterns of the subjects in three
representative experiments corresponding to
three different speeds are depicted in Figs. 2, 4,
and 5. The angles of deviation which have been.
measured in these tracings were entered on each
of the figures.

c A

Ficure 5. Walk pattern in optical environment moving
from 39.1 to 45 radians/min. (see Fig. 2).

Part 2. The problem posed here depended
upon the results of the tests reported in Part 1.
In Part 1 it was found that a person who was
stimulated by a moving environment while he
was walking would become disoriented in his
walking behavior. In Part 2 the question is
asked whether it is necessary for the subject to
be stimulated only during motor activity to bring
about disorientation. This was done by exposing



place in the room at all times to determine if the
drum’s optical influence could override this audi-
tory orienting influence.

Ill. Results

The results were grouped in four parts to
answer four separate questions which arose from
the overall problem. Parts 2, 3, and 4 depended
upon the outcome of the results obtained in Part
1. Since somewhat different experimental pro-
cedures were required in the four parts, their
rationale is briefly introduced at the beginning
of each part.

Part 1. Does the walking path in a stationary
optical environment differ from that in a moving
one? This part of the study was exploratory to
find out whether motor activity as such was af-
fected measurably by this type of visual stim-
ulation.

After establishing the pattern of back and
forth walking with continuously open eyes for
each subject under the control condition of the
stationary drum (Fig. 3), the cylinder was ro-
tated at a constant speed and the walking paths
recorded while the subject kept his eyes open all
the time. Fifty-six tests were made at various
drum speeds. The subjects were divided into
seven groups so that deviations at different speeds
of the drum could be measured and compared.
The speeds into which the tests were grouped
fell into the ranges shown in Table 1.

Taste 1.—Deviation of path of subject, with eyes open
and drum rotating at varying speeds

Mean (+ SD)
of subjects’
angle of
deviation in
degrees

No. of

Range of
subjects

Group radians/min.

WUD OOH
(20 90 00 00 09 00 00 00,

S| socdooc5
9
8
°
i
wa
5

F4
eS

T between groups 1 and 2= 8.1666,
groups in the moving environment

an

.05_ F between
2.5, p M.05

The results are presented in Table 1. It was
evident that motor disorientation occurred con-
sistently when the total visual environment was
moving. This effect was even noticeable in those
subjects who, being exposed to the slowest rota-

Ficure 3. Tracing of a representative experiment qur-
ing a control walk in the stationary optokinetic
drum.

tion (8 to 9 radians/min.), deviated least. These
subjects deviated significantly more than they did
in their control walks (T=8.2, N=8, p<0.01).
Furthermore, the results indicated that there was
a positive association between the degree of dis-


drum induced them to walk. In another proce-
dure, subjects were asked to counteract the influ-
ence of the drum on their walking by timing the
drum’s movement so that the drum’s apparent
speed was noted. If the person walked in the
same direction as the drum’s movement the ap-
parent speed of the drum became slower. It was
reasoned that if the apparent speed of the drum
remained constant or increased for the person,
he should not exhibit disorientation in his
walking.

Although a few subjects were able to counter-
act the influence of the drum by using either or
both of the training procedures, most subjects
reacted unpredictably by overcompensating or
undercompensating.

IV. Discussion

The fact that subjects are influenced by the
drum regardless of whether they are walking or
not indicates that the disorientation induced in
these experiments does not depend on the sub-
ject’s walking during the visual stimulation.
Disorientation has merely been measured by re-
cording the subjects’ motor activity through
walking patterns, and this disorientation will
occur whether the subject is moving or stationary.

The effects of different speeds of visual stim-
ulation require further investigation and quan-
tification. The present results indicate the
subject’s disorientation does not increase linearly
with increments in drum speed.

The apparent different effects among subjects
who have been given the training procedures re-
quire further investigation. At present, it is not
known if these differences may be due to per-
sonality, motivation, or some basic orienting
ability.

The results of this study are applicable to sit-
uations involving the loss or malfunction of
flight instruments under IFR conditions. Under
those conditions, and particularly at night, the
pilot may experience disorientation arising from
the sweep of the beam from the rotating beacon.
The acceleration resulting from inappropriate
roll axis compensation could cause further dis-
orientation arising from labyrinthine stimulation,
thus compounding the problem and leading to
disastrous consequences. The danger has not
been fully recognized in the past. If rotating
beams of light are to be used, beacons should be
arranged to counter-rotate and thus cancel the
disorienting effects.

REFERENCES

1. Brecher, G. A.: Optisch ausgeloste Augen-und Kor-
perreflexe am Kaninchen, Ztschr. f. vergl. Physiol.,
28 :374, 1986.

2. Cortewren, H.: Changes in visual evoked responses
during the fast phase of optokinetic nystagmus in the
rabbit. Vision Res. 9 :803-813, 1969.

8. Gorrz, 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, 1-3 Nov., 1965.

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

5. Nurrats, J. B.: The problem of spatial disorientation.

JAMA, 166 :431-438, 1958.

. Nurratt, James B. and Sanrorp, Witt1aM G.: Spatial
disorientation in operational flight in Medical Aspects
of Flight Safety, ed. Evrard, B., et al. Pergamon
Press, 1959.

7. Prrrs, D. E.: Visual illusions and aircraft accidents.

USAF School of Aerospace Med. Div. Brooks Air
Force Base, Texas. April 1967.

=



AM 69-23

MOTOR EFFECTS FROM VISUALLY INDUCED

DISORIENTATION IN MAN

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

liu

J. Roszrt Dinix, M.D.
Cuter, Crvm AEROMEDICAL
Instrrore

November 1969

Department of Transportation

Released by

[Usege€ md
P. V. Smecet, M.D.
Fepera Am Surceon

FEDERAL AVIATION ADMINISTRATION

Office of Aviation Medicine



the subject to the rotating drum while he stood
still and having him close his eyes immediately
before and during walking. If the subject is
influenced in his walking behavior only by his
exposure to the drum prior to walking, his dis-
orientation may be attributed to the moving
environment.

If the subject walking with closed eyes does
not become disoriented after prior exposure to
the moving drum while standing quietly one
must conclude that the motor activity itself may
be necessary for disorientation to occur.

In principle, the same procedures were fol-
lowed as in the first part. Six subjects were
placed in the drum at a speed of 9-1 radians/
min. First, control tracings of walking patterns
were made with the subject keeping his eyes
continuously open such as in Part 1. Then trac-
ings were recorded in the experimental situation
in which the subject had his eyes open for a
period of 5 seconds while standing and closing
them before starting to walk, keeping them closed
during the walking.

All subjects who walked with closed eyes after
exposure to the moving environment displayed
disorientation (Group II, Table 2). Their de-
viation from the control paths in the stationary
cylinder was significant. In fact, it was almost
as marked (insignificantly different) as the angles
of deviation observed in subjects who walked
with continuously open eyes. The subjective
phenomenon of disorientation did not differ sub-
stantially from that observed among persons
tested with continuously open eyes (Part 1).

Taste 2—Deviation of path of subjects with eyes
closed compared with control and eyes open condition

Group I Group II Group II

Eyes open Eyes closed Eyes open

Subject No. Speed 0 speed 9+1 speed 9+1

radians/min. radians/min. radians/min.

(degrees) (degrees) (degrees)

1 2 17 22
2. 1 3 14
3. 3 9 10
4 2 4 13
5. 3 12 16
6. 2 9 13
13 54 88
2 9 15

T between groups I and II = 3.43340, p M.05
T between groups II and III = 2.51111, p M.05

Part 3. Based on the experience reported in
Part 1 that everyone became disoriented when
walking back and forth with open eyes in the
drum the question arose whether intermittent
periods of nonstimulation would alleviate or
counteract the disorientation.

Six subjects were tested in the drum by walk-
ing back and forth as in Part 1. However, each
time when they had reached the farthest point
of back or forward walking they closed their
eyes and stood quietly for 5 seconds. The control
tracings obtained in the stationary drum were
then compared to those found with the experi-
mental situation of intermittent stimulation.

All subjects who had nonstimulatory “rest
periods” with closed eyes between their walks
deviated significantly from the control pattern
in the stationary environment (Table 3). In
these persons the angles of deviation were almost
as marked as in those who kept their eyes open
continuously, There was no noticeable difference
in subjective disorientation between persons who
closed their eyes intermittently and those who
left them open all the time.

Tapix 3. Deviations of subjects with eyes open only
while wslking compared to the control and the eyes
open only while standing

Group IT

Intermittent Group III
Group I stimulation _—_-Byes open alll
Subject Speed 0 eyes open while the time
No. radians/ walking only. ‘Speed 941
min. Speed 941 radians/min.
(degrees) radians/min. (degrees)
(degrees)
1 2 7 22
2 1 6 4
3 3 9 10
4 2 24 13
5 3 22 16
6 2 ri 18
Total. 18 79 87
Mean. = 2 1B 15

Part 4. Since the methods and results de-
scribed in Parts 1, 2, and 8 permitted an objec-
tive measure of the degree of optical disorienta-
tion in space, it was of interest to find out
whether subjects could be trained to overcome
the disorienting effects.

Two procedures were tried. In one procedure
the subjects were told to counteract the influence
of the drum on their walking behavior by walk-
ing in a direction opposite to that in which the


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MOTOR EFFECTS FROM VISUALLY INDUCED DISORIENTATION IN MAN

I. Introduction

It has long been established by subjective ob-
servations that movements of the optical environ-
ment can produce visual disorientation. An
example would be the sensation of one’s own
movement when looking down on flowing water
from a bridge. In the absence of other clues
which permit correct orientation in space, such
visually evoked disorientation could affect pilots
adversely. This would be especially the case
when optical reference cues, such as the horizon,
are obscured. Presently many aircraft accidents
are attributed to disorientation arising from
vestibular stimulation‘ *. However, it is often
evident that the contribution of visual disorien-
tation to such accidents has not been sufficiently
disinguished from labyrinthine disorientation’ '.
The salient characteristics of optical disorienta-
tion in space therefore need to be defined. There
are two aspects to a proper definition. The first
facet is the subjective sensation of egocentric
dislocalization, which one experiences as a “feel-
ing” of being moved when looking at water pass-
ing under a bridge. By proper feedback
mechanisms from nonvisual sensory input the
person may compensate for his sensation of dis-
orientation and thereupon act appropriately with
respect to his objective environment. The second
facet is the behavioral effect of optically induced
disorientation which a person is not necessarily
aware of subjectively. One of the effects of dis-
orientation might manifest itself in changes of
various types of motor actions leading to an
abnormal motor behavior.

For the above reasons we attempted to eluci-
date the problems of orientation of persons
placed in a moving optical environment. Little
seems to be known about visually induced motor
reactions of man in this situation in which input
from all other sensory modalities remain normal’.
Considerable work on this topic has been done
with animals'*, In the present study walking
was chosen as a simple motor activity to find out
whether it is affected by a movement of the entire

optical surrounding when all stationary visual
clues are eliminated. Disorientation would then
manifest. itself if a person, intending to walk in
a straight line, should deviate from it.

One would expect walking in a straight path
to be unchanged from the normal if stationary
auditory, vestibular, and proprioceptive stimuli
are prepotent over the visual input. On the
other hand, one would expect to find deviations
from a straight walking path if visual stimuli
should override the input from the other sensory
modalities. The purpose of this paper was to
investigate whether or not measurable changes
in motor activity can be visually induced and, if
this should be the case, to explore factors influ-
encing this phenomenon.

II. Methods

The tests were conducted in a cylindrical motor
driven optokinetic drum rotating unidirection-
ally around the vertical axis either clockwise or
counterclockwise (Fig. 1). Part of the top and
bottom were conical in shape to occlude any out-
side stationary objects from the subject standing
inside the drum. The bottom of the drum had
an opening of sufficient: diameter to permit a
person to walk 28 inches in one direction on the
stationary floor beneath the drum. The drum
was suspended so that the bottom of the cone-
shaped rim was 26 inches from the floor. The
drum was 65 inches high and 48 inches in diam-
eter at its widest part. Alternating black and
white vertical stripes 1.5-inch wide constituted
the total visual environment for the subject. In
order to eliminate visual clues from a stationary
light source, the inside of the drum was illumi-
nated from the top with a battery operated
fluorescent light which rotated as part of the
optical environment.

A pen was taped to the outside of the subject’s
left foot. As the subject walked backwards and
forwards in the drum, the pen traced a record
of his walking on paper fixed to the floor under-
neath the drum.



ACKNOWLEDGMENT

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

Qualified requesters may obtain Aviation Medical Reports from Defense Documentation
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