AM 67-19 

ADAPTATION TO VESTIBULAR DISORIENTATION 

VIII. ~~cORIOLIS" VESTIBULAR STIMULATION AND 

THE INFLUENCE OF DIFFERENT VISUAL SURROUNDS 

Approved by 

~~ L BmnmT _DILLE, M.D. 

CHIEF, CIVIL AEROMEDICAL 

INSTITUTE 

William E. Collins 

August 1967 

ReleaBed by 

~MD P. V. SmGEL, M.D. 

FEDERAL Am SURGEON 

FEDERAL AVIATION ADMINISTRATION 

Office of Aviation Medicine 
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 
ADAPTATION TO VESTIBULAR DISORIENTATION 

VIII. "Coriolis" Vestibular Stimulation and the 

Influence of Different Visual Surrounds 

I. Introduction. 

"Coriolis" vestibular stimulation can be produced under controlled laboratory conditions to 

simulate one kind of "pilot's vertigo." The technique 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 results in nystagmus, sensations of disorientation 

and, depending upon ·the visual surrounds, illusory perceptions of motion in other objects. 

The present study was d.esigned to evaluate the 

influence on disorientation of different types of 

head movements made under different aircraftsimulated conditions regarding the visual environment. 

II. Methodology. 

ApparatWJ. 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 ·30°-(from the upright position) could be made 

by each subject in a uniform manner to the lef·t 

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) simuThe assistance of Billy P. Updegraff, David J. D. 

Schroeder, and Ruth Ann Mertens is gratefully acknowledged. 

1 

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 accompanying return-to-upright movements under each 

of the three visual conditions noted above : for 

this group rotaJtion 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 accompanying return movements) during both 

clockwise ( CW) and counter-clockwise (COW) 

rotation. This group was divided into three 

sub-groups of four subjects each, with each subgroup tested under one of the three visual conditions. 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 

CW first while the remaining half began with 

COW rotations. Thus, in Group B, a replication of the experiment with Group A was effected (right head tilts and return movements 

during CW rot·ation) 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 arc and each was accomplished within approximately one second. 

For all tests, rotation velocity of the StilleW emer device was maintained at 12 rpm. This 

level was attained by means of 3° jsec2 angular 

acceleration for 24 seconds. No head movement 

was made until at least three minutes had elapsed 
FIGURE 1. Several views of the stimulator. Upper left: experimental arrangement for the total darkness and the 

wing-tip lights conditions. Upper right: the cabin frame (minus the front panel) has been added. Lower 

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). 

2 
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 separately, i.e., they were regarded as independent 

movements and were separated by the threeminute rest periods. 

Subjects gave verbal reports which were taperecorded during the experiment. They indicated 

the kind of sensation resulting from each movement, 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 sensation 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-directional joy-stick (connected to an X-Y recorder) 

was used during pilot studies to indicate direction and magnitude information, but it was not 

employed in the present work since subjects apparently require considerable practice with such 

a device in order to use it reliably and with 

confidence. 

III. Results and Discussion. 

Group A. Subjects consistently mted 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 Qther :findings.8 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" conditions (see Figure 2). 

The total duration of the sensations of apparent displacement yielded similar results ; return 

movements produced significantly longer subjective reactions ( .05 level) than _did tilts (see 

Figure 2). A breakdown of the sensation into 

primary and secondary aspects was a·ttempted. 

With a given head movement, the sensation began 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) . 

3 

The point at which the subject began to experience a return to the normal position was regarded 

as the end of the primary sensation of displacement 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 17.0 to 81.1 seconds for headreturn 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 maneuver in an aircraft) with some lateral displacement 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 [return-to-upright] means of 50.0°-

75.80 of "dive" with 2.5°-8.8° of lateral displacement. Statistical tests indicated significant 

differences (.05 level) in the magnitude judgments, with the "wing-tip lights" condition producing the greatest amounts of apparent displacement. Possibly ·the highly restricted visual 

field represented by the "wing-tip lights" interacted with the relative motion between the head 

and the lights to produce the judgments of greatest magnitude. The displacement values obtained are considerably higher than those cited 

elsewhere.8 

Group B. Subjects in Group B performed 

both right ·and left head tilts with accompanying 

return movements during both cw and cow 

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 sensation" data which resembled that of Group A. 

Specifically, during CW rotation, return movements from the right produced longer sensations 

than did tilts to the right for the "dark" and 
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FIGURE 3. Average magnitude and direction of apparent displacement for 12 Group A subjects as a result of right-tilt and return-to-upright head movements 

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for both CW and COW rotation for Group B subjects. Different subjects were used for the "Dark", "Light", and "Cabin1' conditions. Intensity ratings 

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in Figure 2. 
"cabin" conditions, and about equally long sensations 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, i.e., return head 

movements yielded stronger sensations than did 

the tilts (see Figure 4). However, this relationship 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 movements for both CW and CCW rotation; this 

difference was considerably less during the "wingtip 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 significant "condition by head-movement" (.01level) 

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 displacement to the right. As in Group A, return movements produced greater apparent displacement 

than did the tilts. The magnitude of the reported displacement resembled very closely the 

values obtained from Group A subjects (see 

Figure 5). 

Left tilts during CW rotation produced sensations primarily of forward displacement ( diving) 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 returnto-upright movements, whereas the latter produced the greatest amount of displacement "forward" or "backward" (Figure 5). It is of interest 

that the apparent lateral displacement to right 

7 

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 OCW rotation, a given head movement yields a sensation opposite that obtained during CW turning (see Figure 6). For 

head movements in both the right and left quadrants, 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 returns) was always to the left. For head movements 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 certain 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 r,ead movement, yaw 

direction, and visual conditi'"n. 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 53.8 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 creates 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" 
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during CW rotation. Four different subjects were used for each of the three experimental conditions. Comparison of right-tilt and return-from-right 

head movements can be made with Group A data in Figure 3. 
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FIGURE 6. Average magnitude and duration of apparent displacement for Group B subjects for right-tilt, left-tilt, and return-to-upright head movements 

during CCW rotation. Subjects were the same as in Figures 4 and 5. 
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 rotation while other subjects were quite disturbed 

(sometimes to the point of nausea) by the same 

movements. (Several subjects had to be eliminated from the study, prior to completing the 

small number of head movements required, due 

to the onset of motion sickness. They were replaced by other subjects.) Also, the conditions 

produced marked differences in the number and 

type of events to which the subjects had to attend. In total darkness, attention could be limited solely to the internal sensations produced by 

the head movements, whereas with the "wingtip 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 inappropriately small amount of apparent displacement. At other times the lights had considerably less apparent velocity but greater apparent 

displacement. These findings have also been 

noted elsewhere.7 •

8 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 differed 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 ( mnging from means of 

33.8°-87.2°) and is in a direction which the subject 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 sensations 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 movement. 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 particular head movement. Such illusions may 

readily occur in aircraft when external visual 

references are not available or when they provide ambiguous information. The importance 

of these "Coriolis" effects has been detailed in a 

number of publications ( e.g.1 •

9 ). 

Most studies of "Coriolis" vestibular responses 

have been concerned primarily with nystagmic 

eye reactions (the directions of nystagmus resulting from various head movements during 

CW and CCW rotation have been detailed by 

Guedry6 ) with relatively limited attention given 

to the subjective effects.2•

5 Guedry and Montague8 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 displacement 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 Montague8 

may be due to one or a combination of the following factors. (1) Subjects in this study had 

no prior practice; those of Guedry and Montague 

received training trials. Data indicate that repetition produces a reduction in the response. 5 

(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 demonstrations 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 spontaneously commented on the usefulness of the 

"cabin" device for pilot-training purposes in 

familiarizing subjects with "Coriolis" vestibular 

effects. 
IV. Summary. 

"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 3Q0 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" 

11 

in a luminous "cabin" which was secured about 

the rotating device. Verbal estimates of the illusions 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 movement as opposed to another depended upon the 

turning direction (yaw-axis) of the stimulator 

(CW or CCW) and upon the visual surrounds. 
REFERENCES 

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

Williams & Wilkins, 1961. 

2. BoRNSCHEIN, H. Theorie and praktische Bedeutung 

des vestibularen Coriolis-Effektes. Mschr. Ohrenheilk., 1962, 96, 45-49. 

3. BORNSCHEIN, H. and SCHUBERT, G. Objektivierung 

und Analyse des vestibularen Coriolis-Effektes. Z. 

Biol., 1954, 107, 95-107. 

4. BoRNSCHEIN, H. and ScHUBERT, G. Die Reizparameter 

des vestibularen Coriolis-Effektes. Z. Biol., 1958, 

110, 269-275. 

5. BORNSCHEIN, H. and SCHUBERT, G. Die Richtung des 

vestibularen Coriolis-Effektes. Z. Biol., 1962, 118, 

145-160. 

6. GUEDRY, F. E. 

Stimulation in 

Habituation to Complex Vestibular 

Man : Transfer and Retention of 

12 

Effects from Twelve days of Rotation at 10 RPM. 

Percept. Mot. Skills (Monog. Suppl. 1-V21), 1965, 

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