Taste 2. Measures of primary nystagmus following
the termination of each rotatory stimulus for cats.
Each response value is a mean of responses to an
acceleration and a deceleration stimulus, Stimuli
were 4°/sec* for 1.2, 3, 9, 15, 21, or 80 seconds.

Time From End of Stimulus to End of Primary
Nystagmus (Sec)

Cat 12 3.0 9.0 15.0 21.0 30.0
108 10.9 12.4 14.6 10.6 81 6.0
109 5.9 8.3 82 5.4 4.0 16
110 18.5 73 9.2 12.0 5.0 23
it 71 111 88 65 43 12
112 3.0 12.4 11.6 15.7 12.2 10.8
113 28 11.8 9.8 9.4 6.0 38
114 8.2 11.6 9.3 8.0 13.6 6.8
115 10.2 8.0 10.2 106 13.1 9.0
116 115, 12.1 14.2 15.3 124 13
7 76 3.0 82 9.3 6.2 5.0
us 8.9 12.3 13.3 13.3 12.5 12.1
119 10.4 10.7 72 5.0 72 2.5
M= 88 101 10.4 10.1 87 65

Time From End of Stimulus to Start of Secondary
Nystagmus (See)

108 15.6 15.4 20.8 15.60 145 18.2
109 79 16.9 13.5 9.9 6.5 62
110 15.9 6.6 12.9 6.0 8.4 6.7
i 15.0 16.8 12.6 10.8 75 (10.6
112 —_ 14.6 175 24.4 20.4 18.1
113 15.7 18.3 14.1 116 9.0 15
14 12.5 12.7 14.7 25.4 154 15.6
115 17.3 19.5 14.6 16.7 15.0 14.0
116 13.6 16.9 21.3 175° «1540 161
117 11.2 18.0 14.8 12.6 13.0 © 15.6
118 93 16.3 15.3 15.5 16.4 7
119 15.2 14.9 11.8 114 95 a1
M= 13.6 15.6 15.3 14.8 12.6 12.2

Beats of Primary Nystagmus After End of Stimulus

108 2.0 12.0 19.0 125 115 6.5
109 15 7.0 9.0 6.5, 2.5 1.0
110 3.0 3.0 6.5 65 4.0 3.0
11 25 10 85 70 4.0 2.0
112 25, 8.0 140 185 «16.5 95,
113 2.0 15 9.5 9.0 5.0 3.0
114 55 8.5 12.0 75 17.0 5.5
115 45 7.0 85 9.5 16.5 10.5
16 55 8.0 16.0 18.0 9.5 18.5
117 4.0 5.0 —_ 8.5 5.0 12.0
118 12.0 15.5 17.0 19.5 19.0 15.0
119 4.0 8.0 5.5 45 7.0 15

— > — rr

M= 41 8.0 14 10.6 o8 73

Taste 8. Measures of primary nystagmus following
the termination of each rotatory stimulus for human
subjects. Each response value is a mean of re-
sponses to an acceleration and a deceleration stim-
ulus. Stimuli were 4°/sec* for 1.2, 3, 9, 15, 21, or
30 seconds.

Time From End of Stimulus to End of Primary
Nystagmus (Sec)

Subject 12 3.0 9.0 15.0 21.0 80.0

Pa 22.0 11.0 17.3 32.0 168 223
Da 12.6 25.2 42.4 541 646 ©6458
Br —_ 28.8 20.5 25.7 87.5 = 29.6
Do 18.3 19.6 38.9 513 36.3 © 89.8
Ch 13.1 25.1 40.0 33.0. 245 23.9
Ro 13.6 41.3 28.4 34.9 44.2 40.5
Ve 10.9 62.2 44.0 413 884 87.9
Te —_ 20.9 42.6 26.7 33.1 272
Dt 318 42.0 44.4 484 40.1 85.7
Sa 21.3 22.3 55.6 44.1 32.8 288
Pz 73 29.1 51.9 40.3 89.2 28.5
Dy 17.6 46.3 42.4 45.6 33.7 29,2
M= 16.9 812 39.5, 898 368 32.4

Time From End of Stimulus to Start of Secondary
Nystagmus (Sec)

Pa —- —§$— S §- — — - 1
Da — -—_— $s — — — es
Br —- —- —-  —

Do >- CO Cr Ore rr
Ch —_ —_ 30.6. 428 283 27.1
Ro —_ _ 12.7 413 514 45.4
Ve _ —_— 48.8 46.1 402 381
Te _— 11.4 23.0 Wl (3841 35.9
Dt 818 40.2 44.4 588 401 35.7
Sa 213 —_— — 32.2 829 288
Pa —_— —_— 51.7 419 39.2 358
Dy —_— — 50.4 50.0 33.7 3819
M= * * 46.8 413 875 © 87.2
Beats of Primary Nystagmus After End of Stimulus
Pa 13.0 13.0 19.5 36.5 39.0 27.5
Da 10.0 25.0 66.5 825 940 81.0
Br _ 27.0 115 29.0 33.0 29.5
Do 9.0 13.0 39.5, 47.0 425 39.0
Ch 15 29.5, 47.0 455 425 37.0
Ro 85 24.5, 43.0 50.5 70.0 62.5
Ve 45, 30.0 41.0 44.0 37.0. 82.5
Te —_— 23.0 58.0 46.0 515 38.5
Dt 12.0 39.5 55.5 63.5 595 | 55.5
Sa 20.0 315 78.5 73.0 52.5 540
Pz 4.0 12.0 84.5 34.0 285 24.0
Dy 15.0 20.5 47.0 510 46.5 |= 48.5
M>= 10.4 24.0 44.7 50.2 49.7 43.7

*Too few scores on which to base a mean.



representation of movement, due to central and
peripheral differences, will differ slightly in
different animals.

The functional significance of the secondary
process is not established. Some pathological
conditions undoubtedly yield a central imbalance
of spontaneous input from the two ears, and the
“secondary process” may serve to readjust the
point of homeostatic balance. Some complex
motions of the head and body may terminate
with minor residual cupula deflections, and this
could require minor shifts in the point of bal-
ance between the two ears, which would be ac-
complished too slowly by the elasticity of the
cupula. Tolerance to an increased level of ves-
tibular stimulation encountered in land, sea, and
air travel may require a suppression at some
level of vestibular inflow, and it is possible that
this secondary process serves this function. It
has been shown that standard test stimuli ad-
ministered after an angular acceleration are
influenced in proportion to the duration of the
preceding angular acceleration, and it may be
assumed that this finding is another manifesta-
tion of the “secondary process.” Moreover, with
repetitive angular accelerations, the peaks of
both primary and secondary nystagmus in cats

diminish and shift toward earlier occurrences.*°
This suggests that the secondary process en-
croaches more and more upon the primary reac-
tion and thus limits the magnitude and duration
of the primary reaction with repetitive stimula-
tion. In humans, there are large individual
differences in secondary nystagmus. If the sec-
ondary reaction is a manifestation of an adap-
tive process which serves to limit the primary
reaction, it may prove to be an indicator, among
people with comparable histories of motion ex-
posure, of individual differences in ability to
habituate to repetitive vestibular stimulation.

VI. Summary

A direct relationship between duration of ac-
celeration and (a) decline of response during
acceleration, (b) rate of decline of response after
acceleration, and (c) magnitude of secondary
reaction, is regarded as an indication of a cen-
tral process which limits a prolonged vestibular
primary reaction. The process is manifested by
its influence on relatively basic reflex reactions
(nystagmus) in the cat, and is more prominently
manifested in man by its influence on sensory
perception.


40 -

30 F

PRIMARY NYSTAGMUS

—
e.
/ ee HUMANS
° e

SUBJECTIVE RESPONSES
4——A PRESENT STUDY

4— — 4 GUEDRY, CRAMER,
& KOELLA, 1958

POST-STIMULUS RESPONSE DURATION IN SECONDS

tL
lof o——° Oo ~~a
—$__
PRIMARY NYSTAGMUS °
5 FROM CATS
at 1 1 L 1 1 1 i L J
5 10 15 20 25 30 35 40 «45 ~~ 50
TIME IN SECONDS

Ficure 3. Duration of the post-stimulus subjective and nystagmic reactions obtained in this study are com-

pared with subjective data from an earlier study. The abcissa represents stimulus duration.

Functions de-

picted for the two sets of subjective data and for primary (slow-phase displacement) nystagmus from cats are

in close agreement.

where the mean subjective turning scores from
the present study are presented along with sub-
jective data obtained in a previous study. In
this earlier study,'* subjects had been trained in
making subjective reports, whereas the present
subjects had no preliminary practice. The rise
and decline in duration of human nystagmus
and subjective response as stimulus duration in-
creases is also matched fairly well by the change
in temporal characteristics of nystagmus in the
eat, also shown in Figure 3, Reference to Tables
2 and 8 shows that, in both man and cat, time
elapsed from stimulus termination to onset of
secondary nystagmus increases and declines in a
manner which approximately parallels duration
of the primary reaction.

Secondary nystagmus was not evident in the
recordings of any of the human subjects for the
1.2 and 3 sec stimuli, and several subjects gave
no secondary response to the 30 sec stimulus.
However, frequency of otcurrence of secondary
nystagmus increased with stimulus duration, and
this may be interpreted as evidence for a rela-
tionship between stimulus duration and intensity
of secondary response in humans similar to, but
more variable than, that observed in the cat. In
comparison with secondary nystagmus of the
cat, the secondary nystagmus in man has a later
onset, lower average intensity (relative to man’s
primary reaction), and seems to be more subject
to individual differences.

Tables 2 and 38 suggest that the number of



1007 PRIMARY menews

8° SEC

Sec
SEC

SEC
3 — SEC
o \ soo 12 sec
Fe

Pe STIMULUS DURATION
2

$

2

3

2

=

o

5

2

my

a

¢

=

=

'

z

3

3

a

3 6 9 12 1S 18 21 24 27 30 33 36 39 42 45 46 SI 54 57 60 63 66 69 72 75 78 BI 84 B87 90 93 96

20 SECONDARY NYSTAGMUS. STIMULUS: 4°/ SECT

-— kaye
a Rare cees ee eee SS one eral
3 6 9 12 IS 18 21 24 27 30 33 36 39 4245 48 5! 54 57 60 63 66 69 72 7H 78 BI 84 87 90 93 96 99 102 0S
TIME IN SECONDS

Ficure 2. Time-course plots of slow-phase displacement per 8-sec interval for 12 human subjects exposed to 6
stimulus durations of 4°/sec* angular accelerations.

dent for any duration (compare with Figure 1).
tions occurs after stimulus termination.

No decline of nystagmus during stimulation is evi-

Note that the peak response for the three shortest dura-
No secondary responses were evident for the 1.2 and 3 sec stimuli

and not all subjects showed secondary nystagmus for the longer stimuli.

The slow-phase velocity of primary and sec-
ondary nystagmic responses was plotted for each
of the 6 stimulus durations (Figure 1). For
the 21 and 30 sec stimuli, there was a slight de-
cline in response during constant angular ac-
celeration, Consistent with data from cats in
the earlier experiment,’ it appears that the nys-
tagmic response reaches maximum intensity be-
tween 15 and 20 sec and declines after this, even
though the stimulus is of constant magnitude
and direction.

The peak magnitude of secondary nystagmus
appears directly related to the duration of the
angular acceleration. Secondary responses were
obtained from all but one cat for the 6 stimulus-
duration conditions; the exception (cat 112)
gave no secondary nystagmus following the 1.2
second stimulus.

B. Human Subjects

Figure 2 shows little or no decline in human
nystagmus during constant angular acceleration

irrespective of stimulus duration. This is con-
sistent with human results of earlier studies,>***
but it is in contrast with results from cats in
which nystagmus declined after about 20 sec of
constant angular acceleration.

With brief stimuli (1.2 sec and 8 sec), it ap-
pears that in both man and cat the slow-phase
velocity of nystagmus continues to increase
(“overshoots”) after the stimulus terminates
(Figures 1 and 2), whereas, with prolonged
stimuli, slow-phase velocity of nystagmus de-
clines immediately after (in humans) or before
(in cats) the stimulus terminates (Figure 1).

As stimulus duration is increased up to about
15 seconds, the duration of the post-stimulus
primary nystagmus increases. With longer
stimuli, the duration of the post-stimulus pri-
mary response declines. In this respect human
primary nystagmus corresponds fairly well in
its temporal characteristics with the human sub-
jective response. This is shown in Figure 3


man when prolonged high-magnitude angular
accelerations are used.)

It is parsimonious and reasonable to assume
that a single process accounts for (a) the decline
in response during prolonged angular accelera-
tion, (b) the increased response decline following
prolonged acceleration, and (c) the increased
secondary response following prolonged accelera-
tion. The possibility that the cupula endolymph
system is under-critically damped, contrary to
the common supposition, would explain a sec-
ondary response, but this seems at variance with
much of the evidence for the over-damped Tor-
sion Pendulum analogy of van Egmond, Groen,
and Jongkees*? and could not explain findings
(a) and (b). To explain these results on the
basis of cupula deflection, it would be necessary
to assume that the stiffness of the cupula in-
ereases during prolonged constant angular ac-
celeration. Van Egmond, et al?* have proposed
that events within the endorgan (either bioelec-
tric, biochemical or plastic changes within the
cupula) could account for secondary responses,
and this possibility cannot be ruled out. Lowen-
stein** has reported that increasing cupula de-
flection in elasmobranch initiates neural activity
“in one after the other previously silent units”
which often adapt themselves rapidly, Adrian*
and recently Melvill Jones,’ recording from the
vestibular nuclei in cats, found little evidence for
rapid adaptation. However, Cappel* has noted
that slow declines in some units recorded in the
vestibular nuclei of cats correspond temporally
to declines in human subjective data. The pos-
sibility that there is a diminished sensory inflow
during prolonged cupula deflection in cats
remains open.

In man, one aspect of the vestibular reaction
(subjective velocity) declines while another as-
pect (nystagmus) does not decline during pro-
longed acceleration.* From this, it does not
seem reasonable to attribute the decline of the
one response to a suppression of sensory inflow.
(Some reservations are necessary in this inter-
pretation because average curves of different
groups of subjects form the basis of the conclu-
sion. Subjective and nystagmic data from the
same subjects should be compared and studied
for the presence of correlation.) Aschan and
Bergstedt? have evidence which implicates the
central nervous system in secondary responses.
Prolonged primary responses induced by uni-

lateral caloric stimulation should provide an
opportunity for adaptive changes within the
cupula; yet Aschan and Bergstedt? reported
little or no secondary nystagmus with unilateral
caloric stimuli, whereas bilateral hot/cold caloric
stimuli and rotational stimuli, yielding primary
responses of equivalent length, produced sec-
ondary responses.

Although secondary nystagmus (and appar-
ently associated response modulation) in man
and cat are probably attributable to the central
nervous system, it remains quite possible that
some of the differences between man and cat are
attributable to differences in the properties of
endorgans; e.g., the shorter primary nystagmic
response in cats (irrespective of stimulus dura-
tion) is probably attributable to a greater cupula
spring-action in cat, Response parameters of
the central nervous system may be conditioned
or inherently matched to the response parameters
of the cupula-endolymph system so that the
shaping of responses to unusual stimuli may be
similar in form but on a different time base in
different animals.

The conditions under which the “secondary
processes” have been demonstrated, viz. pro-
longed constant angular acceleration, are seldom,
if ever, encountered in natural movement. Even
a single, brief, unidirectional angular accelera-
tion followed by constant velocity does not oc-
cur in natural movement and, as noted in the
present study, intensity of nystagmus continues
to increase briefly beyond the termination of
short unidirectional stimuli. In natural move-
ment, any brief angular acceleration is imme-
diately followed by angular acceleration of
opposite sign which returns the cupula toward
its position of static equilibrium. Hence, in the
case of either brief unidirectional stimuli or
prolonged unidirectional stimuli, the vestibular
reactions fail to follow the theoretical’? cupula
deflection. However, this does not necessarily
signify either an inadequate response: system
within the range of natural movements or a
gross error in theoretical cupula mechanics. The
departure from expected results signifies a range
of unnatural stimuli which is not accurately
followed due to either inaccurate sensory detec-
tion or unfaithful central following of the input,
or both. Because the natural periods of move-
ments of various animals are different,’® it is
quite possible that the ranges of accurate sensory



AM 67-7

ADAPTATION TO VESTIBULAR DISORIENTATION

VI. Eye-Movement and Subjective Turning Responses to
Varied Durations of Angular Acceleration

Fred E. Guedry, Jr., Ph.D.
William E. Collins, Ph.D.

Approved by Released by
J. Roserr Dux, M.D. P. V. Srecen, M.D.
Cuter, Crvr, AEROMEDICAL Feperan Air Surazon
Insrrrvte
May 1967

FEDERAL AVIATION ADMINISTRATION
Office of Aviation Medicine





a

9

10.

11.

REFERENCES

Apzian, E. D., 1943: Discharges from vestibular re-
ceptors in the cat. J. Physiol., 101, 389.

AscHan, G. and Beresrepr, M., 1955: The genesis of
secondary nystagmus induced by vestibular stimuli.
Acta Soe. Med. Upsal., 60, 113.

. Carpet, K. L., 1966: Determination of physical con-

stants of the semicircular canals from measurement
of single neural unit activity under constant angular
acceleration. In Second Symposium on the Role of
the Vestibular Organs in the Exploration of Space.
NASA Report SP-115, 229.

. Coriins, W. E., 1964: Primary, secondary, and caloric

nystagmus of the cat following habituation to rota-
tion. J. comp. physiol. Psychol., 57, 417.

. Cortins, W. E., and Guepry, F. H., 1962: Arousal

effects and nystagmus during prolonged constant an-
gular acceleration. Acta oto-laryng. (Stockh.), 54,
349,

. Cortins, W. E., and Guepry, F. E., 1967: Duration

of angular acceleration and ocular nystagmus from
cat and man. I. Responses from the lateral and the
vertical canals to two stimulus durations, Acta oto-
laryng. (Stockh.), in press.

Corzins, W. E., and Hurrman, H. W., 1964: Design
and performance characteristics of a mechanically
driven vestibular stimulator. OAM Report No. 64-15,
Oklahoma City, Oklahoma,

Cortins, W. E., and Uppeorarr, B. P., 1966: A com-
parison of nystagmus habituation in the cat and the
dog. Acta oto-laryng. (Stockh.), 62, 19.
Dopez, R., 1923: Habituation to rotation.
Psychol., 6, 1.

Ex, J., Jonaxers, L. B. W., and Kurs, J.A.J., 1960:
On the effect of continuous acceleration. Acta oto-
laryng. (Stockh.), 51, 416.

Groen, J. J., 1960: Problems of the semicircular canal
from a mechanico-physiological point of view. Acta
oto-laryng., Supl. 163, (Stockh.) 59.

J. exp.

12. Guepry, F. E., and Ceran, 8. J., 1959: Derivation of
“subjective velocity” from angular displacement esti-
mates made during prolonged angular accelerations:
Adaptation effects. U. 8. Army Med. Res. Lab. Re-
port No. 376, Fort Knox, Kentucky.

Guepry, F. E., Cramer, R. L., and Koruna, W. P.,
1958: Experiments on the rate of development and
the rate of recovery of apparent adaptation effects
in the vestibular system. U. 8. Army Med, Res. Lab.
Report No. 338, Fort Knox, Kentucky.

14. Guepry, F, E., and Lavuver, L. §, 1961: Vestibular
nystagmus during constant angular acceleration. J.
appl. Physiol., 16, 215.

Henrixsson, N, G., Fernanpez, C., and Konur, R. L,
1961: The caloric test in the cat. Acta oto-laryng.
(Stockh.), 58, 21.

Lowenstein, O., 1956: Comparative physiology of the
otolith organs. Brit. Med. Bull., 12, 110.

MELvitt Jones, G., 1967: On the dependence of oculo-
motor response upon the neural response of the vesti-
bular system. Paper presented at Third Symposium
on the Role of Vestibular Organs in Space Explora-
tion, Pensacola, Florida (Jan, 24-26, 1967).

Metvitt Jones, G., and Spetts, K. E,, 1963: A theo-
retical and comparative study of the functional de-
pendence of the semicircular canal upon its physical
dimensions. Proc. Roy. Soc, B, 157, 403.
Mrrrermarer, R., and Rossserc, G., 1956: Vesti-
bularesuntersuchungen mit schwellennaken Beschleue-

13.

1b.

16.

1.

18.

19.

gungsreizen, Arch. Ohren-Nasen-U. Kehlkopfh., 168,
313.
20, Montanpon, A., and Fumeavx, J., 1957: Valeur dia-

gnostique comparative des nystagmus per- et post-
rotatoires 4 l’épreuve giratoire liminaire. Prac. oto-
rhino-laryng., 19, 556,

21, vAN Eomonp, A. A. J., Groen, J. J., and JonaxEEs,
L. B. W., 1949: The mechanics of the semicircular
canal, J. Physiol., 110, 1.



beats of secondary nystagmus is more closely
related to the duration of primary post-stimulus
nystagmus than to the duration of the stimulus.
This is in contrast to the maximum slow-phase
velocity of secondary nystagmus which seems
related to the stimulus duration, at least in the
cat (see Figure 1). The decline in number of
secondary beats with stimuli longer than 15 sec
may signify an encroachment of the secondary
reaction on the primary reaction.

Primary nystagmus in the cat is shorter in
duration and has a lower beat-frequency than
that of man for the range of stimuli investigated.
There is also a pronounced difference between
man and cat in regard to the intensity-ratio of
secondary to primary nystagmus, the ratio being
higher for the cat.

A log plot of nystagmus slow-phase velocity
with respect to time also shows the cat to have

30 cr
255 \ Human [O—9 30 SEC
20 f, NS e@--© 9 SEC
rsh \ _
Fis t\. cat [4-4 30 SEC
8 Mae ONG a--A 9 SEC
a VON,
Be lop \
r] N,
oe os
23 4
SE \
co}
ao Spr \
2m \
S a
ye \
ato \
rio \
ao ‘
1hé
a~ \ \
a \ vi
| \\
Ss \ e

14
3.6 9 [2 15 18 21 24 27 30 33 3639 42
TIME IN SECONDS

Ficure 4. Log plots of slow-phase eye velocity follow-
ing two stimulated durations for cat and human
subjects. Data represent nystagmus measured from
the point of stimulus termination and thus depict
the rates of response decay. Decay is more rapid
in cats and the longer stimulus duration produces
more rapid declines.

a substantially different rate of decline of nys-
tagmus (lower time constant) than man for
comparable stimuli (see Figure 4). It also ap-
pears that the slope of nystagmus decline for both
man and cat changes as a function of stimulus
duration, the. longer stimuli producing post-
stimulus nystagmus with a higher rate of decay
(lower time constant).

V. General Discussion

Because neurophysiological data from cats are
sometimes applied to the explanation of reactions
in man, it is important to compare the same
response variables in men and cats exposed to
identical vestibular stimuli. Nystagmus in cats
declined during prolonged constant angular ac-
celeration in spite of efforts to maintain alert-
ness, whereas nystagmus in alert men did not
decline during prolonged angular acceleration;
the rate of decline of primary vestibular nys-
tagmus following each stimulus was greater in
cats than in man; the ratio of secondary to pri-
mary nystagmus was higher in cat than in man.

If it is assumed that secondary nystagmus
reflects a process which develops during the pri-
mary reaction and opposes its continuation, then
all of the differences between man and cat may
be due to this secondary process in cat having a
more direct control of nystagmus than does its
counterpart in man. The characteristics of sub-
jective data reported by man resembled the
alterations of nystagmus in cats during and after
prolonged angular accelerations? and in some
respects the nystagmus of man deviates from
both the nystagmus of cat and the subjective
responses of man during and after these unusual
stimuli. It appears that the hypothesized sec-
ondary process exerts a control on man’s sensory
experience, i.e, the perceived angular velocity,
comparable to the control of nystagmus in the
cat. This is not to say that the nystagmus of
man is completely without the modulating in-
fluence of this secondary process because the rate
of decline of both post-stimulus primary nys-
tagmus and the occurrence of secondary nys-
tagmus were influenced in man by the duration
of the stimulus. However, the control is appar-
ently less consistent and, hence, probably less
direct for the range of stimuli used in the present
experiment. (Subsequent experiments have il-
lustrated a pronounced secondary nystagmus in


Scoring. Slow-phase displacement of the eyes
was scored by measuring the peak to base-line
distance for each beat of nystagmus and sum-
ming these values for 3-sec intervals. Time
measurements were also made from the end of
each stimulus (a) to the end of the primary
response and (b) to the start of the secondary
nystagmus. The number of beats of primary
nystagmus which followed stimulus termination
was tabulated.

IV. Results and Discussion

A. Cats

Measures of both response time and the number
of beats of primary nystagmus following stimu-
lus termination appear in Table 2. Post-stimulus
responses of greatest duration and magnitude
occurred when stimulus durations were between
3 and 15 sec with the maximum post-stimulus
primary response occurring, in general, with
stimuli of 9 sec duration.

907 PRIMARY NYSTAGMUS
80 ca
r * o—+ 30 SEC
a X——x 21 SEC
7OF 1 \ 15 SEC
—~—: \ ‘. 9 SEC
60F o—s 3 SEC
a \
a \ s+ 1.2 SEC
& 50r . STIMULUS DURATION
o \
i} x
40F
g |¥ \
2 oly \
30F e
< \ \
2 . \ ° x
2 20F /N 4 \ \
oN \ \ \
@ 10 |” ‘ % ° \ ‘
x \ N \ N \
a ~ ~“ \ .
' er ee >> —e
z 3 6 9 I2 15 18 21 24 27 30 33 36 39 42 45 48 51 54
a
307 = SECONDARY NYSTAGMUS 2
y STIMULUS: 4°/SEC
>
| x" oS AGE FOR 12 CATS
2p AVERAGE FO
_ ‘x.
Rept NERS =
Hor wa i RR
tag =}
N, _——
aN - SS eae

9 12 15 18 21

TIME

24 27 30 33 36 39 42 45 48 SI

54

IN SECONDS

Freure 1. Time-course plots of slow-phase eye displacement per 3-sec interval for 12 cats exposed to 6 stimulus

durations of 4°/sec’ angular accelerations.
begin to decline during the stimulus.
ulus termination,

2

For the 21 and 30 sec durations, responses reach a peak and
For the two shortest durations, the peak response occurs after stim-
Peak magnitude of the secondary reactions appears related to stimulus duration,


ADAPTATION TO VESTIBULAR DISORIENTATION

VI. Eye-Movement and Subjective Turning Responses to
Varied Durations of Angular Acceleration

I. Introduction

Ocular nystagmic responses elicited by angular
acceleration have been found to be different in
cat and in man.é With prolonged stimuli (36
sec), a rise and decline of nystagmus during
stimulation was obtained from cats for both
Jateral- and vertical-canal stimulation. Human
subjects did ‘not exhibit a comparable decline
during prolonged stimulation. Nystagmic reac-
tions of the cat thus resembled the subjective
(rather than the nystagmic) reactions of human
subjects,2#.2.19.20

At least part of the difference noted above in
regard to primary nystagmic reactions appears
related to the prominent secondary nystagmus
which characterizes responses of the cat to angu-
lar accelerations. Secondary nystagmus is op-
posite in direction to the primary response, and
it may reflect a process which develops during,
and opposes continuation of, the primary re-
action.

The present investigation represents an exten-
sion of the earlier study.? A range of stimulus
durations was used to clarify relations between
stimulus duration, the rate of decline of primary
nystagmus, and the intensity of secondary nys-
tagmus, and to compare further vestibular pro-
cesses in cat and man.

IL. Methodology

A. Cats

Apparatus. Rotational stimulation was pro-
vided in a light-proof room with the Huffman
Rotation Device.’ Angular accelerations and
decelerations were 4°/sec? separated by 54 sec of
constant velocity. Animals were tested in pairs
(with their heads at the center of rotation) by
means of a set of tiers.

Restraint. Restraint was effected by the method
of Henriksson, Fernandez, and Kohut*® and in
the manner described elsewhere.°

Recording. An Oftner Type R Dynograph re-
corded horizontal components of eye movements
from needle electrodes inserted by the outer
canthi. A 3-sec time constant was used in
amplification.

B. Human Subjects

Apparatus. A Stille-Werner RS-8 rotator was
programmed to provide accelerations and de-
celerations of 4°/sec* separated by 2 min of con-
stant velocity.

Recording. An Offner Type T polygraph (time
constant: 8 sec) recorded horizontal components
of eye movements from surface electrodes taped
by the outer canthi.

III. Procedure

Each of 12 cats and 12 human subjects re-
ceived 6 rotatory trials comprising 4°/sec? ac-
celerations and decelerations for 1.2, 3, 9, 15, 21,
and 30 sec. Rotation was always counterclock-
wise and the order of presentation of the stimu-
lus durations was counterbalanced among pairs
of subjects as indicated in Table 1.

Taste 1. Order of presentation of stimulus durations
(in seconds). Durations varied from 1.2 to 30 sec.
All angular accelerations were 4°/sec* and rotation

was always counterclockwise. Only the lateral
canals were stimulated.

Human Trials
Subjects Cats 1 2 8 4 5 6

Pz&Ch 108&109 12 30 9.0 150 210 300
Dy&Do 110&111 3.0 9.0 150 210 300 12
Sa&Br 112&118 9.0 15.0 210 3800 12 30
Dt&Da 114&115 15.0 210 300 12 30 90
Te& Ro 116&117 21.0 300 12 30 90 150
Ve& Pa 118&119 300 12 30 90 150 210

None of the subjects had been used in previous
vestibular experiments. Human subjects (6 men
and 6 women) were instructed to signal onset.
and cessation of their rotatory experiences by
means of a signal key.



ACKNOWLEDGMENTS

Dr. Guedry is Chief of Experimental Psychology, Research Department,
USN Aerospace Medical Institute, Pensacola, Florida; Dr. Collins is Chief,
Psychology Laboratory, Civil Aeromedical Institute.

This study was conducted at the Civil Aeromedical Institute in Okla-
homa City with the technical assistance of Billy P. Updegraff, Ruth Ann
Mertens, and Kathryn Quattlebaum.

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