Ill. Results.

In all tests the subjects displaced the subjective
median in the same direction in which the optical
environment was moving. All subjects were in-
fluenced by higher speeds of optical stimulation
and set the subjectively determined median at a
greater distance from the objective median than
they did at the slower speeds (see Table 1).
Even at the slowest speed used, the subjects
placed the rod a significantly greater distance
from the objective median than they did in the
control tests in which the optical environment
was stationary (t=8.2454 P<.05).

IV. Discussion.

It is clear from these findings that a person
may be influenced by his optical environment so
that objects are displaced with respect to an ob-
jective reference to the egocenter. These experi-
ments provide quantitation of the observation
that the optical environment plays an important
role in orientation in space. For this reason it
is strongly advised that the subjective optical

space should never be equated with the objective
space when the visual environment is in motion,
though under normal stationary conditions the
subjective and objective space practically coin-
elde,

Tasuz 1.—Placements of the Subjective Median Plane
under Conditions of Various Speeds of Rotational
Optical Stimulation

Placement of median (+ = clockwise — =
Counterclockwise) N = 12

speed (clockwise) constant error Deviation
radians/minute (degrees)

0 (control) —0,08 3.77

941 +6, 53* 9.43
1841 +8.59 8.46
2741 +10. 22 11,74
361 +11.00 9.40
4541 +11.90 11.65

* Significantly greater than control (t = 8.2454 p<.05).

REFERENCES

1, Brecher, M. H. and G. A. Brecher: Motor Effects
from Visually Induced Disorientation in Man. FAA
Office of Aviation Medicine Report No, AM-69-23,
1969.

2. Brecher, M. H. and G. A. Brecher: Quantitative

Evaluation of Optically Induced Disorientation.

FAA Office of Aviation Medicine, AM—70-2, 1970,

Bruell, J. H. and G. W. Albee: Effects of Asymmetri-

cal Retinal Stimulation on the Perception of the

Median Plane. PERCEP. MOT. SKILLS 5:133-139,

1955.

-

4. Hering, Ewald: Spatial Sense and Movements of the

Eye. AM. ACAD. OPTOM. pp 60-65, 1942.

Howard, I. P. and W. B. Templeton: Human Spatial

Orientation, London, John Wiley and Sons, 1966, pp

280-289.

Moser, Royce: Spatial Disorientation as a Factor in

Accidents in an Operational Command. AEROSP.

MED. 40:174-176, 1969,

7. Tschermak, A. (v): Optischer Raumsinn. HAND-
BUCH DER NORMALEN UND PATHOLOGISCHEN
PHYSIOLOGIE, 12:834-995, 1931.

so

2


TECHNICAL REPORT STANDARD TITLE PAGE

T. Report No. 2. Government Accession No. 3. Recipient's Cotelog No.
FAA-AM-71-22

4, Title and Subtitle 5. Report Date

EFFECT OF A MOVING OPTICAL ENVIRONMENT ON THE April 1971
SUBJECTIVE MEDIAN 6. Performing Organization Code

7, Author's) 8. Performing Organization Report No,
M. Herbert Brecher, M.A., Gerhard A. Brecher, M.D.,

Ph.D.

9. Performing Organization Name and Addre 10. Work Unit No.

University of Oklahoma Medical Center
Department of Physiology and Biophysics TN
Oklahoma City, Oklahoma 73104

+ Contract or Grant No.

FA67AC-2699-1
13. Type of Report and Period Covered

12. Sponsoring Agency Name and Address

Office of Aviation Medicine OAM Report
Federal Aviation Administration
800 Independence Avenue, S. W, 14.” Sponsoring Agency Code

Washington, D.C, 20590
15. Supplementary Notes

16. Abstract

The placement of a point in the median vertical plane under the influence of a
moving optical environment was tested in 12 subjects. It was found that the
median plane was displaced in the same direction as the movement of the visual
environment when the environment was moved at speeds ranging from 9 £1
radians/minute to 45 + 1 radians/minute. It was established that unidirectional
movements of the total optical environment always caused a spatial disorientation
with respect to external visual reference points.

V7. KeyWords Median plane subjective, 18. Distribution Statement

Median plane objective, Median point Availability is unlimited. Document may

setting, Egocentric localization, be released to the National Technical

Orientation in space, Disorientation in Information Service, Springfield, Virginia

space, Visual illusions, Straight ahead 22151, for sale to the public.

subjective, Straight ahead objective

19. Security Classif. (of this report) 20. Security Classif. (of this page) 21. No. of Pages | 22, Price
Unclassified Unclassified 2 $3.00

Form DOT F 1700.7 (8-69)





EFFECT OF A MOVING OPTICAL ENVIRONMENT ON THE
SUBJECTIVE MEDIAN

I. Introduction.

The point in the visual space which is judged
subjectively to lie straight ahead in the median.
plane has been studied under various conditions
in the past.? Armin von Tschermak conducted
some of the earliest intensive investigations of
the conditions causing the displacement of the
subjective straight ahead from the objective
straight ahead.? More recently the “sensory
tonic motor theory” has been proposed to explain
the displacement of the subjective median plane.*

According to Ewald Hering, who did the first
studies of the setting of a point in the median
plane, this point may be established with small
errors when an individual is sitting in a normal
upright position The purpose of the present
study was to determine if movement of the opti-
cal environment influences the setting of the
straight ahead.

The ability to orient oneself to optical refer-
ence points external to oneself, especially the
ground and horizon during flight, is often neces-
sary. Most accidents attributed to disorientation
have occurred when visual references were ob-
secured in either hazardous weather or at night
and disorientation is often experienced among
pilots who fly through clouds or in formation.*

Though the emphasis in the past has been
placed on the effects of vestibular and proprio-
ceptive stimulation on disorientation, recently
the potency of optical stimulation on orientation
has been given greater attention.*?

II. Methods.

A rotating cylindrical drum was used for the
purpose of eliciting disorientation. The top and
the bottom of the drum were conical in shape to
eliminate all stationary stimuli which may be
viewed by the subjects inside of the drum. The
bottom of the drum had an opening 36’ in
diameter and was suspended so that the bottom
was 28” from the floor. The drum was 4’ in

diameter and 5’5” high. The inside of the drum
had alternating 1.5” black and white vertical
stripes.

The subjects were seated in the drum and
their heads were held in a fixed position by a
headband which was secured to a metal bar above
the subject; thus, their heads were held so that
the point which was objectively straight ahead
could be established.

A 1%” by 6’ vertical rod was moved by the
experimenter in a semicircular path in front of
the subject and the subject was required verbally
to direct the experimenter so that the rod ap-
peared exactly in the subject’s median plane.
The rod was guided in a predetermined path by
a semicircular metal ring at the base of the rod.
Each time the rod was placed in the position of
“straight ahead” as instructed by the subject this
placement was recorded by the experimenter and
the rod was moved out of the subject’s field of
view. The side from which the rod entered the
subject’s visual space was alternated with each
trial.

In order to determine the constant error‘ or
average distance of displacement from the objec-
tive straight ahead, the subject placed the rod
three times for each test condition, Each test
was performed at one preselected drum speed.
Errors in a counterclockwise direction were as-
signed negative values and errors in a clockwise
direction were assigned positive values.

Twelve visually normal college students were
used as test subjects. After being given the
instruction that they were to direct the experi-
menter to move the rod to a “straight ahead”
position, they entered the optokinetic drum. For
each subject a control measurement was obtained
in which the subject placed the rod in a straight
ahead position when the drum was standing still.
Thereafter each subject then placed the rod while
the drum was moving at speeds ranging from
9-1 to 45-41 radians/minute.