REFERENCES

1, ArMstRoNG, H. G, Aerospace Medicine. Baltimore:

Williams & Wilkins, 1961.

2, Bornscuein, H, Theorie and praktische Bedeutung
des vestibularen Coriolis-Effektes. Mschr. Ohren-
heilk., 1962, 96, 45-49.

8. Bornscuemn, H, and Scuuserr, G. Objektivierung
und Analyse des vestibularen Coriolis-Hffektes, Z.
Biol., 1954, 107, 95-107.

. BorNscHeIn, H. and Scuvusert, G. Die Reizparameter
des vestibularen Coriolis-Effektes. Z. Biol., 1958,
110, 269-275.

5. BornscHein, H. and Scuuserr, G. Die Richtung des
vestibularen Coriolis-Effektes. Z. Biol., 1962, 118,

145-160.

6. Guzpry, F. E. Habituation to Complex Vestibular
Stimulation in Man: ‘Transfer and Retention of

i

Effects from Twelve days of Rotation at 10 RPM.
Percept. Mot. Skills (Monog. Suppl. 1-V21), 1965,
21, 459-481.

Gurpry, F. E., Graysrer, A. and Couns, W. E.
Reduction of Nystagmus and Disorientation in Hu-
man Subjects. Aerospace Med., 1962, 33, 1356-1360.

Guepry, F. E. and Montacur, BE. K. Relationship
between Magnitudes of Vestibular Reactions and
Effective Coriolis Couples in the Semicircular Canal
System. USAMRL Report No. 456, Ft. Knox, Ky.,
1960.

Nurratt, J. B. and Sanrorp, W. G. Spatial Dis-
orientation in Operational Flight. In Medical Aspects
of Flight Safety, Evrard, E., Bergeret, P., and Van
Wulfften Palthe, P. M. (Eds.) N. Y¥.: Pergamon,
1959, 73-91.


from the termination of the acceleration. At
least three minutes intervened from the end of
one head movement to the start of another, Tilt
and return movements were considered sepa-
rately, i.e., they were regarded as independent
movements and were separated by the three-
minute rest periods.

Subjects gave verbal reports which were tape-
recorded during the experiment. They indicated
the kind of sensation resulting from each move-
ment, the direction and magnitude (in degrees)
of apparent displacement, and gave signals for
the onset and termination of their sensations.
In addition, ratings of the intensity of each sen-
sation were obtained by having the subjects rate
as 100 percent the sensation resulting from one
of the first two head movements (a tilt and a
return-to-upright); all other sensations were
judged against that standard. An omni-direc-
tional joy-stick (connected to an X-Y recorder)
was used during pilot studies to indicate direc-
tion and magnitude information, but it was not
employed in the present work since subjects ap-
parently require considerable practice with such
a device in order to use it reliably and with
confidence.

Il. Results and Discussion.

Group A. Subjects consistently rated the
sensations produced by 30° head tilts toward the
right shoulder as weaker than the sensations
produced by return movements of the head to
the upright position. These differences were
statistically significant by analysis of variance
(.01 level) for the three test conditions and
agree with other findings.’ The presence of the
“wing-tip lights” produced stronger sensations
for both tilt and return movements than did
either the “total darkness” or the “cabin” con-
ditions (see Figure 2).

The total duration of the sensations of appar-
ent displacement yielded similar results; return
movements produced significantly longer subjec-
tive reactions (.05 level) than did tilts (see
Figure 2). A breakdown of the sensation into
primary and secondary aspects was attempted.
With a given head movement, the sensation be-
gan almost instantly and maximum apparent
displacement was reached very quickly. After
some period of time, the subject felt himself
returning to a normal (“level flight”) position
(although he had actually remained motionless).

The point at which the subject began to experi-
ence a return to the normal position was regarded
as the end of the primary sensation of displace-
ment and the start of the secondary reaction.
For tilts to the right, mean primary reactions
ranged from 23.8 to 31.9 seconds for the three
conditions; for head-return movements the range
was 29.6 to 35.4 seconds. The mean total time
for primary and secondary reactions combined
ranged from 48.7 to 78.5 seconds for tilts to the
right and from 77.0 to 81.1 seconds for head-
return movements.

During CW rotation, right-tilts of the head
produced sensations of apparent displacement
primarily in a backward direction (similar to a
climbing maneuver in an aircraft) accompanied
by lateral displacement to the right. Return
movements resulted in sensations of apparent
forward displacement (similar to a diving ma-
neuver in an aircraft) with some lateral dis-
placement to the right. The average apparent
magnitude of displacement was considerable (see
Figure 3), ranging from [head-tilt] means of
42.9°-60.4° of “climb” with 12.7°-20.6° of lateral
movement to [veturn-to-upright] means of 50.0°—
75.8° of “dive” with 2.5°-8.8° of lateral dis-
placement. Statistical tests indicated significant
differences (.05 level) in the magnitude judg-
ments, with the “wing-tip lights” condition pro-
ducing the greatest amounts of apparent dis-
placement. Possibly the highly restricted visual
field represented by the “wing-tip lights” inter-
acted with the relative motion between the head
and the lights to produce the judgments of great-
est magnitude. The displacement values ob-
tained are considerably higher than those cited
elsewhere.*

Group B. Subjects in Group B performed
both right and left head tilts with accompanying
return movements during both CW and CCW
rotation. In agreement with the data obtained
from Group A, return head movements from
the right tilt to the upright position during CW
rotation yielded significantly stronger sensations
by analysis of variance (.05 level) than did the
tilts to the right (see Figure 4). The same. set
of head movements yielded “duration of sensa-
tion” data which resembled that of Group A.
Specifically, during CW rotation, return move-
ments from the right produced longer sensations
than did tilts to the right for the “dark” and



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“cabin” conditions, and about equally long sen-
sations for both tilt and return movements in
the “wing-tip lights” condition (compare Figures
2 and 4).

Right head tilts and return movements during
CCW rotation in total darkness produced the
same relationship of “intensity of sensation”
ratings as that of CW rotation, ie., return head
movements yielded stronger sensations than did
the tilts (see Figure 4). However, this relation-
ship was reversed for both the “wing-tip lights”
and “cabin” conditions where the head tilts to
the right during CCW rotation produced stronger
sensations than the return-to-upright movements.
Similarly, in total darkness, left tilts of the head
yielded weaker sensations than the return move-
ments for both CW and CCW rotation; this
difference was considerably less during the “wing-
tip lights” condition and ratings were about
equal for the two head movements (for both
directions of rotation) in the “cabin” condition.
These results found statistical expression in sig-
nificant “condition by head-movement” (.01 level)
and “rotation-direction by head-movement” (.05
level) interactions. Thus the relative intensity
of the sensations occasioned by certain tilt and
return head movements appeared to be affected
by visual information.

In agreement with data from Group A, head
tilts to the right during CW rotation produced
sensations of apparent displacement backwards
(climbing maneuver) with additional lateral
displacement to the right. Return-from-right
head movements resulted in apparent forward
displacement (diving) with less lateral displace-
ment to the right. As in Group A, return move-
ments produced greater apparent displacement
than did the tilts. The magnitude of the re-
ported displacement resembled very closely the
values obtained from Group A subjects (see
Figure 5).

Left tilts during CW rotation produced sen-
sations primarily of forward displacement (div-
ing) as opposed to the apparent backward
displacement (climbing) resulting from head
tilts to the right. As with head movements in
the right quadrant, tilts to the left produced
greater lateral displacement than did the return-
to-upright movements, whereas the latter pro-
duced the greatest amount of displacement “for-
ward” or “backward” (Figure 5). It is of interest
that the apparent lateral displacement to right

tilts was always to the right (in agreement with
data from Group A) while the apparent lateral
displacement to left tilts was to the left for the
“dark” and “cabin” conditions, but to the right
for the “wing-tip lights” condition. A similar
result was obtained during CCW rotation.

During CCW rotation, a given head move-
ment yields a sensation opposite that ob-
tained during CW turning (see Figure 6). For
head movements in both the right and left quad-
rants, return-to-upright during CCW turning
tended to produce the greatest forward-backward
displacement, while tilting movements produced
the greatest lateral displacement; however, these
differences between tilts and returns were not so
great as those obtained during CW stimulation
nor were they perfectly consistent. The lateral
displacement experienced as a result of head
movements in the left quadrant (tilts and re-
turns) was always to the left. For head move-
ments in the right quadrant, however, lateral
displacement was to the right for the “dark”
and “cabin” conditions, but to the left for the
“wing-tip lights” condition. This parallels the
finding for CW rotation noted above. Thus cer-
tain types of visual information appear to modify
the lateral aspect of the direction of apparent
displacement.

The degree of apparent pitch forward was
considerable, ranging from means of 33.8° to
86.2° depending upon the head movement, yaw
direction, and visual condition. For climbing
sensations the mean pitch angle ranged from
45.6° to 87.2° (see Figure 5). The primary
aspect of the sensations lasted from 13.0 to 24.7
seconds for “climb”, and from 12.5 to 34.7 seconds
for “dive”; the total time of the sensation (from
start of head movement to the point when the
subject felt he was in “level flight” again) ranged
from means of 24.0 to 58.8 seconds for “climb”,
and from 28.0 to 71.3 seconds for “dive.” Thus,
the sensations are long-lasting and the apparent
pitch is of considerable magnitude (compare
with data from Group A). In addition, the
fact that the direction of apparent displacement
is in a plane at right angles to both the direction
of yaw and the direction of head movement cre-
ates a problem of interpretation for the subject;
the direction of apparent displacement does not
seem to be directly related to the direction of his
head movement.

The Sensations. The “intensity of sensation”



AM 67-19

ADAPTATION TO VESTIBULAR DISORIENTATION
VIII. “CORIOLIS” VESTIBULAR STIMULATION AND
THE INFLUENCE OF DIFFERENT VISUAL SURROUNDS

William E. Collins

Approved by Released by

P. V. Smeorz, M.D.
Crier, Crvm. AEROMEDICAL Fevers Am Surcron
InstiroTs

August 1967

FEDERAL AVIATION ADMINISTRATION
Office of Aviation Medicine



ratings reported by the subjects were probably
not made on an equivalent basis for the three
conditions. This is partly due to the fact that
some subjects seemed to enjoy the sensations
produced by head movements made during ro-
tation while other subjects were quite disturbed
(sometimes to the point of nausea) by the same
movements. (Several subjects had to be elimi-
nated from the study, prior to completing the
small number of head movements required, due
to the onset of motion sickness. They were re-
placed by other subjects.) Also, the conditions
produced marked differences in the number and
type of events to which the subjects had to at-
tend. In total darkness, attention could be lim-
ited solely to the internal sensations produced by
the head movements, whereas with the “wing-
tip lights” the apparent motion of the lights also
had to be considered. In the latter situation, the
lights appeared to move in the same direction
as the apparent displacement of the subject;
however, the apparent velocity of the light and
its extent of movement differed with different
head tilts. For example, the lights sometimes
appeared to have very high velocity but an in-
appropriately small amount of apparent displace-
ment. At other times the lights had consider-
ably less apparent velocity but greater apparent
displacement. These findings have also been
noted elsewhere.”® Under the “cabin” condition,
the lights appeared simply to move with the
“window frame” and the subject experienced a
visually reinforced sensation of displacement in
that he “saw” the cabin tilt with him. Thus,
the ratings assigned to the various sensations
were actually based on sets of events which dif-
fered among subjects and among the conditions.
General Discussion. These data indicate that
a strong sensation of apparent displacement
may accompany relatively small head movements
during an angular velocity of 72°/sec (12 rpm).
In addition, the experienced displacement is of
considerable magnitude (ranging from means of
33.8°-87.2°) and is in a direction which the sub-
ject does not readily associate with the head
movements. Thus, due to the so-called “Coriolis”
forces, lateral head movements during rotation
about an earth-vertical axis produce illusions of
climbing or diving, while nodding motions of
the head under the same condition produce sen-
sations of apparent tilt to the right or to the left.
Additional illusions are experienced when the

10

“wing-tip lights” are viewed. The lights appear
to move at different velocities and to different
terminal points depending upon the head move-
ment. Under the “cabin” viewing condition, the
lights appear immediately to follow the apparent
maneuver of the “cabin” which is clearly seen
as tilted in a given direction following a par-
ticular head movement. Such illusions may
readily occur in aircraft when external visual
references are not available or when they pro-
vide ambiguous information. The importance
of these “Coriolis” effects has been detailed in a
number of publications (e.g.»*).

Most studies of “Coriolis” vestibular responses
have been concerned primarily with nystagmic
eye reactions (the directions of nystagmus re-
sulting from various head movements during
CW and CCW rotation have been detailed by
Guedry*) with relatively limited attention given
to the subjective effects.*> Guedry and Mon-
tague® presented information regarding both
reactions but reported relatively low magnitudes
of apparent displacement (approximately 15°
of displacement for head tilts of 30° during
10 rpm rotation). In this study, apparent dis-
placement averaged three or more times this
value. Differences in the magnitude of the
“diving” and “climbing” sensations obtained here
as compared with those of Guedry and Montague®
may be due to one or a combination of the fol-
lowing factors. (1) Subjects in this study had
no prior practice; those of Guedry and Montague
received training trials. Data indicate that repe-
tition produces a reduction in the response.*
(2) Displacement ‘values in this study represent
the verbal estimates of the subjects whereas
Guedry and Montague used joy-stick movements
as their basic data. (3) The rate of rotation
was higher in this study (12 rpm vs. 10 rpm).

It should be noted that a considerable number
of licensed pilots (many with prior military
fighter aircraft experience) have been exposed to
the “cabin” condition during laboratory demon-
strations and have given verbal estimates of
displacement which are very similar to those
reported by the naive subjects in this study.
Parenthetically, these individuals have spon-
taneously commented on the usefulness of the
“cabin” device for pilot-training purposes in
familiarizing subjects with “Coriolis” vestibular
effects.


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Upper left: experimental arrangement for the total darkness and the

Figure 1. Several views of the stimulator.
Upper right: the cabin frame (minus the front panel) has been added. Lower

wing-tip lights conditions,
left: front panel added to cabin frame with the subject’s head in the right tilt position. Lower right: interior
view of the cabin frame condition (wing-tip lights were viewed through the “window” of the cabin).




ADAPTATION TO VESTIBULAR DISORIENTATION
VIII. “Coriolis” Vestibular Stimulation and the
Influence of Different Visual Surrounds

I. Introduction.

“Coriolis” vestibular stimulation can be pro-
duced under controlled laboratory conditions to
simulate one kind of “pilot’s vertigo.” The tech-
nique involves the use of a device capable of
rotation. If a subject makes head movements
during such rotation, he produces an unusual
stimulation of the semicircular canals which re-
sults in nystagmus, sensations of disorientation
and, depending upon the visual surrounds, il-
lusory perceptions of motion in other objects.
The present study was designed to evaluate the
influence on disorientation of different types of
head movements made under different aircraft-
simulated conditions regarding the visual en-
vironment.

II, Methodology.

Apparatus. A Stille-Werner RS-3 Rotation
Device was modified by: (a) attaching a light
source which simulated an approaching aircraft
in night flight (red and green “wing-tip” lights
and a red-“rotating beacon”); (b) developing a
special head-holder and chin-rest arrangement
so that, when properly adjusted, head movements
of 80°.(from the upright position) could be made
by each subject in a uniform manner to the left
and to the right; (c) a cabin-frame, filling the
visual field, which could be placed around the
seated subject. The front of the cabin contained
a simulated instrument panel and a rectangular
opening (window) through which the light
source was viewed. The interior of the cabin
was coated with luminous paint (see Figure 1).
Subjects were always seated directly over the
axis of rotation.

Procedure. Subjects were tested under three
sets of conditions: (a) total darkness; (b) simu-

The assistance of Billy P. Updegraff, David J. D.
Schroeder, and Ruth Ann Mertens is gratefully ac-
knowledged.

lated aircraft lights viewed in an otherwise
totally dark room; (c) simulated aircraft lights
viewed through the “window” of the luminous
“cabin” in an otherwise totally dark room. There
were two experimental groups comprised of 12
subjects each. The age range was 21-27 years.

Group A subjects (9 males and 3 females)
performed head tilts to the right with accom-
panying return-to-upright movements under each
of the three visual conditions noted above: for
this group rotation was always clockwise. A
counterbalanced design was used—half of the
subjects began with their heads upright while
the other half began with their heads already
in the tilted position.

Group B subjects (10 males and 2 females)
performed right and left head tilts (with ac-
companying return movements) during both
clockwise (CW) and counter-clockwise (CCW)
rotation. This group was divided into three
sub-groups of four subjects each, with each sub-
group tested under one of the three visual condi-
tions. Half of the subjects began with left tilts
and half with right tilts, and within each of the
sub-groups, half of the subjects were rotated
OW first while the remaining half began with
CCW rotations. Thus, in Group B, a replica-
tion of the experiment with Group A was ef-
fected (right head tilts and return movements
during CW rotation) and additional information
was obtained.

The number of head movements made by each
subject was limited to prevent the effects of
habituation from influencing the data. All head
movements were 30° of are and each was accom-
plished within approximately one second.

For all tests, rotation velocity of the Stille-
Werner device was maintained at 12 rpm. This
level was attained by means of 3°/sec? angular
acceleration for 24 seconds. No head movement
was made until at least three minutes had elapsed



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Iv.

“Coriolis” vestibular stimulation was used to
produce disorientation and simulated “pilot’s
vertigo” under controlled laboratory conditions.
During angular velocities of 72°/sec, subjects
made 30° lateral head movements under three
conditions: (a) in total darkness; (b) while
viewing simulated aircraft lights in an otherwise
totally dark room; and (c) while viewing the
simulated aircraft lights through a “window”

Summary.

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in a luminous “cabin” which was secured about
the rotating device. Verbal estimates of the il-
lusions of “diving” or “climbing” maneuvers
resulting from the head movements ranged from
a@ mean of 33.8° to 87.2° depending upon the
head movement and the visual conditions for
different groups of subjects. Relative intensity
of the sensations occasioned by one head move-
ment as opposed to another depended upon the
turning direction (yaw-axis) of the stimulator
(CW or CCW) and upon the visual surrounds.