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Freure 1. Representative tracings of vertical nystagmus from two cats. Vertical bars
through the tracings demarcate the stimulus periods (5°/sec’ for 12 sec).

3

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and body of each animal was in the plane of
rotation. By changing the position of the ani-
mals 180° after the habituation trials, the same
set of semicircular canals was stimulated but the

orientation of the otoliths (and other gravi-
receptors) was changed. Habituation was spe-
cific to the practiced direction of nystagmus and
to the practiced head (otolith) position.

REFERENCES

1, Berestept, M., 1961: The effect of gravitational
force on the vestibular caloric test. Acta Otolaryng.
(Stockh.), 58, 551-562.

2, Brown, J. H., 1965: Acquisition and retention of
nystagmic habituation in cats with distributed ac-
celeration experience. J. comp. physiol. Psychol.,
60, 340-353.

3. Capps, M. J. and Corrins, W. E., 1965: Bffects of
bilateral caloric habituation on vestibular nystagmus
in the cat. Acta Otolaryng. (Stockh.), 59, 511-580.

4, Comtins, W. E., 1964a: Nystagmus. responses of
the cat to rotation and to directionally equivalent
and non-equivalent stimuli after unilateral caloric
habituation. Acta Otolaryng. (Stockh.), 58, 247-258.

5. Cottins, W. E., 1964b: Primary, secondary and

caloric nystagmus of the cat following habituation

to rotation.. J. comp. physiol. Psychol., 57, 417-421.

Cortins, W. E., 1967: Effects on vestibular habitua-

tion of interrupting nystagmic responses with op-

posing stimuli. J. comp. physiol. Psychol., 64, 308-

312.

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

8, Corzins, W. E. and Uppecrarr, B. P.," 1966: A
comparison of nystagmus habituation in the cat and
the dog. Acta Otolaryng. (Stockh.), 62, 19-26,

9. Crampton, G. H. and Brown, J. H., 1964: Repeated
vertical semicircular canal stimulation does not
habituate horizontal nystagmus in cat. Acta Oto-
laryng. (Stockh.), 58, 441-448,

10. Guepry, F, E., 1965: Habituation to complex vesti-
bular stimulation in man: ‘Transfer and retention
of effects from twelve days of rotation at 10 rpm.
Percept. Mot. Skills (Monog. Suppl. 1-V21), 21,
459-481,

11. Guepry, F. E., 1966: Influence of linear and angular
accelerations on nystagmus. In Second Symposium
on the Role of the Vestibular Organs in Space Ex-
ploration, NASA Report SP-115, 185-198,

e

12, Guepry, F. E,, Coutins, W. E. and Graysiet, A.,
1964: Vestibular habituation during repetitive com-
plex stimulation: A study of transfer effects. J.
appl. Physiol., 19, 1005-1015.

13, Henrixsson, N. G., Fernanpez, C, and Kouut, R. L.,
1961: ‘The caloric test in the cat, Acta Otolaryng.
(Stockh.), 58, 21-32,

Jonexers, L. B. W. and Puiupszoon, A. J., 1962:
Nystagmus provoked by linear accelerations, Acta
Physiol. Pharmacol. Neerlandica, 10, 289-247.

15. Jonaxees, L. B. W. and Putripszoon, A. J., 1963:
The influence of position upon the eye-movements
provoked by linear accelerations. Acta Otolaryng.
(Stockh.), 56, 414-419,

16. Jonexers, L. B, W. and Puucreszoon, A. J., 1964:
Electronystagmography. Acta Otolaryng. (Stockh.);
Suppl. 189, 109 p.

1%, Lansperc, M. P., Guepry, F. E. and Graypie, A.,
1964: The effect of changing the resultant linear
acceleration relative to the subject on nystagmus
generated by angular acceleration. USN-NASA
Joint Report, No. 99, Pensacola, Fla.

18. Merrens, R. A, and Corzins, W. B., 1967: Uni-
lateral caloric habituation of nystagmus in the cat:
Effects on rotational and bilateral calorie responses,
Acta Otolaryng. (Stockh.), 64, 281-297.

19, Niven, J. 1, Hixson, W. ©. and Coznera, M. J, 1965:
An experimental approach to. the dynamics of the
vestibular mechanisms. In Symposium on the Role
of the Vestibular Organs in the Exploration of
Space, NASA Report, SP-77, 43-56.

20. Owapa, K. and Oxvuso, K., 1963: The otolithic
reaction on nystagmus by caloric stimulations. In:
Contribution to the Vestibular Physiology and Vesti-
bular Test (Japan society of vestibular research),
Acta Otolaryng. (Stockh.), Suppl. 179, 1-6.

21. Puiuipszoon, A. J., 1968: Some experiments on
the function of the labyrinth I. Proc. Oto-Rhino-
Laryng., 24, 344-847.

14,


habituation trials were conducted in accordance
with the schedule in Table 1. During one pre-
and post-habituation trial the animals were posi-
tioned on their sides with the right half of their
heads and bodies oriented upwards; in the re-
maining pre- and post-habituation trial the right
side was oriented downwards. Pre- and post-
habituation trials comprised accelerations and
decelerations of 5°/sec? for 12 sec separated by
a 2-min period of constant velocity. Half of the
animals were rotated CW; the other half, CCW.
Within these two groups, half of the animals
received the first pre- and post-habituation test
in the “right-side up” position and the second
pre- and post-habituation test in the “left-side
up” position; the order was reversed for the
remaining animals, The use of both accelerations
and decelerations permitted the elicitation of
both up-beating and down-beating nystagmus
under each of the two head-position conditions,
Since the head position was changed 180° from
the first pre- and post-trial to the second pre-
and post-trial, the same sets of vertical semi-
circular canals were stimulated on each occasion,
but the position of the otoliths was shifted.

Habituation trials comprised 15 CCW ac-
celerations of 5°/sec? for 12 sec followed by 1
min of constant velocity and a sub-threshold de-
celeration (0.15°/sec?). Half of the animals
were rotated “right-side up”; the other half,
“left-side up.” Thus for each animal only one
direction of nystagmus was elicited, with the
otoliths maintained in the same position, during
habituation trials.

Recording was accomplished with an Offner
Type R Dynograph using 3-sec time constants
in amplification. Prior to rotation each cat was
placed first on its right side, then on its left side,
in an optokinetic stimulator to obtain calibration
data for converting slow-phase measurements of
rotation-induced nystagmus to degrees of eye

Tasie 1.

movement as outlined elsewhere.* In addition
to slow-phase displacement, the number of nys-
tagmic eye movements and the duration of the
response to angular accelerations were obtained.

III. Results and Discussion.

Samples of pre- and_ post-test oculographic
tracings are presented in Figure 1. Mean re-
sponse scores for slow-phase, frequency, and
duration measures of nystagmus appear in Table
2. Mean pre-test scores for the 3 measures were
set at 100 per cent and the post-test data were
then expressed as percentages of the pre-tests.
These percentage relationships appear in Figure
2.

All post-test responses showed an average de-
cline but the direction of nystagmus repeatedly
elicited with the head (otoliths) in the “habitua-
tion” position declined more. Pre- to post-test
relative change scores were computed for each
animal under each condition and t tests were
performed (Table 3). For duration values,
which showed the smallest overall pre- to post-
test changes, no significant differences were ob-
tained among the comparisons. Other data have
also shown that duration scores are relatively
poor indicators of habituation effects.%+*

For both frequency and slow-phase measures,
the direction of nystagmus elicited with the
otolith position used in the habituation series
declined significantly (p <.01) more than: (a)
the same direction of nystagmus with the otolith
position changed, and (b) the opposite direction
of ‘nystagmus with the otoliths in either the
“habituated” or the “unhabituated” position.
There were no statistically significant differences
among the remaining comparisons.

These data indicate that habituation of rota-
tion-induced vertical nystagmus occurs in cats,
but that the habituation is specific to the direc-

Outline of test conditions. Pre- and post-habituation stimuli were accelera-

tions and decelerations of 5°/sec® for 12 sec separated by 2 min of constant velocity.
Habituation stimuli were accelerations of 5°/sec? for 12 sec (decelerations were

sub-threshold).
Pre-1 and Post-1 Pre-2 and Post-2 Habituation Series
Cats (accel and decel) (accel and decel) (15 trials-accel only)
211 & 212 CW —left side up CW—right side up CCW—right side up

218 & 214 CW—right side up
215 & 216 CCW—left side up
217 & 218 CCW —right side up

CW —left side up
CCW—right side up
CCW—left side up

CCW—right side up
CCW—left side up
CCW—left side up



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ADAPTATION TO VESTIBULAR DISORIENTATION:
IX. Influence of Head Position on the Habituation
of Vertical Nystagmus

William E. Collins, Ph.D.

Approved by Released by

M.D. P. V. Smern, M.D.

J. Roser Drutz,
Curer, Civin AEROMEDICAL FeveraL Arr SurcEon

InsTITUTE

March 1968

Department of Transportation

FEDERAL AVIATION ADMINISTRATION
Office of Aviation Medicine



Tante 2, Mean slow-phase displacement of the eyes, number of nystagmic eye move-

ments, and response duration on pre- and post-habituation trials for 8 cats.

Data

for both the habituated and the unhabituated directions of nystagmus are presented
for the head position used during habituation trials and for a 180° change in head

position (“unhabituated head position”).

Habituated Head Position:
Direction of. Nystagmus

Unhadituated Head Position:
Direction, of Nystagmus

Measure Test Habituated Unhabituated Habituated Unhabituated
Slow-phase Pre 448 372 496 325
(Degrees) Post 240 311 395 264
Number of Pre 30 30 30 28
Beats Post 18 26 27 26
Duration Pre 23 21 22 23
(Seconds) Post 18 20 21 21
‘Taste 8. Results of t tests for the various combinations of head position and direction

of nystagmus (Hab=“Habituated” ; Unhab=“Unhabituated”).

Comparisons t
Head Nystagmus Head Nystagmus Blow- Number
Position Direction v8. Position Direction Phase of Beats Duration

Hab Hab vs. Hab Unhab 3.51* 3.07" 1.94
Hab Hab vs. Unhab = Unhab 5.16* 4.39* 2.15,
Hab Hab vs. Unhab Hab 3.12* 5.00* 1.89
Hab Unhab~ vs. Unhab Hab 0.14 1.03 0.42
Hab Unhab_~svs. Unhab Unhab 0.54 0.27 0.00
Unhab Unhab_ vs. Unhab Hab 0.45 0.07 0.32,

*.01 level of significance.

tion of the reaction and to the position of the
otoliths. The results do not appear due to arousal
factors which might have been occasioned by
changing the position of the animals; additional
trials conducted with several of the cats con-
firmed the difference between the “practiced”
and the “unpracticed” positions. The otoliths
(and perhaps other nonspecific gravi-receptors)
thus appear to exercise considerable influence on
activity of the semicircular canals, probably by
altering the neural pattern of stimulation. ‘These
results may also provide a basis for an explana-
tion offered for the failure to obtain transfer of
habituation from one mode of stimulation to
another2* It has been suggested that a possible
factor in the failure of habituation of nystagmus
to repeated caloric irrigations (primarily of the
lateral canals) to transfer to rotational stimula-
tion of the same canals may be due to differences
in the position of the otoliths. That is, during
calorization procedures, the heads of the stimu-

lated animals are placed in a position tilted back
from that of normal carriage to orient the lateral
canals in an optimal position for caloric stimula-
tion. During rotation, the animals’ heads are
anteverted to place the lateral canals in the plane
of rotation. The lack of transfer of habituation
from one condition to the other may be due to
the difference in the patterns of stimulation oc-
casioned by varying the position of the otoliths.
At any rate, the consistency of the results ob-
tained from the animals tested here seems to
point to an important interaction in the habitua-
tion process between specific and nonspecific
gravi-receptors and responses from the semi-
circular canals.

Iv. Summary.

Habituation of vertical ocular nystagmus by
means of repeated angular acceleration was ac-
complished with a group of eight cats. For all
habituation trials, the saggital plane of the head



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ADAPTATION TO VESTIBULAR DISORIENTATION:

IX. Influence of Head Position on the Habituation

of Vertical Nystagmus*

I. The Problem.

Interactions of linear and angular accelerations
are frequently experienced by pilots during air-
craft maneuvers. Recent evidence from human
studies conducted on centrifuges” has indicated
that stimulation of the otoliths (detectors of
linear acceleration) may influence the magnitude
of nystagmic reactions initiated by the semi-
circular canals (detectors of angular accelera-
tion). Data based on nerve resections in rabbits”?
showed that the otoliths exert some regulatory
functions on nystagmus. Other studies involving
rabbits and human subjects on the parallel swing
(an otolith stimulator) have reported nystagmus
produced by linear accelerations when the eyes
of the subjects were deviated laterally, either
voluntarily in humans or as the result of a com-
pensatory reaction occasioned by placing animals
on their sides2%"*"2 Niven, Hixson, and Cor-
reia®® have demonstrated clear horizontal nys-
tagmus from humans to periodic linear accelera-
tion and Guedry"t has related these findings to
his own work (involving rotation about an earth-
horizontal axis) in which nystagmus produced
by angular acceleration was augmented or di-
minished depending upon whether the gravity
vector was to the left or right of the subject.
Further, under conditions of bizarre vestibular
stimulation of human subjects (the so-called
“Coriolis” effects occasioned by head movements
during rotation), failures to obtain transfer of
habituation have been reported from a practiced
quadrant of head movement to an unpracticed
one” and from a practiced direction of rotation

TThe animals used for this experiment were lawfully acauired
‘and treated in accordance with the “Principles of Laboratory
‘Animal Care” issued by the Animal Facilities Standards Com-
mittee of the Animal Care Panel, U.S. Department of Health,
Education and Welfare, Public Health Service, March 19
‘Assistance rendered by Billy P. Updegraff and Kathryn Quat!
baum during the conduct of this study is gratefully acknowl
edged.

to an unpracticed one. In these latter studies
it was hypothesized that stimuli from several
sources (including the otoliths) may have sig-
nificantly influenced the development of certain
demonstrated compensatory reaction patterns in
ways which would result in minimal transfer of
habituation.

The present study was designed to test a dif-
ferent aspect of the possible interactions between
the otoliths and the semicircular canals. Spe-
cifically, it was desired to examine the influence
of repeated semicircular canal stimulation with
the otoliths in one position, on the response to
stimulation of the same canals with the position
of the otoliths changed. Habituation of ocular
nystagmus (a response decline resulting from
repeated stimulation) has been clearly demon-
strated in the cat under a number of different
rotatory and caloric conditions.°8252538 Tt
has been shown that this habituation is relatively
specific to the direction of response repeatedly
elicited,®* to the plane of the response,’ and
to the type (rotatory or caloric) of stimulus
used.4538

II. Method.

Eight cats, all farm-reared and of mixed
breed, were each restrained by a modification
of the method of Henriksson, Fernandez and
Kohut*? prior to testing. The restraint modifi-
cation involved the use of spacers to assure that
head position remained invariant when the cats
were placed on their sides. Fur around the left
ocular orbit was shaved off and surface electrodes
were taped above and below the eye. Animals
were tested in pairs on the Huffman Rotation
Device’ by means of a tier arrangement.?

Each animal was positioned with its head over
the turning axis of the rotator and with the
saggital plane of its head and body in the plane
of rotation. Two pre-habituation and two post-