group of birds the first pre- and post-test rota-
tions were conducted with “beak down” for two
birds (one CW, the other CCW), and with
“beak up” for the remaining two birds (one CW,
the other CCW). The second pre- and post-test
were in the same direction of rotation as the
first for a given bird, but the animal’s position
was changed by 180°. Pre- and post-tests com-
prised accelerations and decelerations of 10°/

sec.? separated by two min. of constant velocity.
Thus, during pre- and post-tests both directions
of nystagmus were elicited (one direction during
acceleration, the other during deceleration) for
the two head and body positions (“beak down”
and “beak up”). During the habituation series,
however, only one direction of nystagmus was
permitted to occur and the head and body were
maintained in a single position.

TaBuE 2.—Outline of test procedure for stimulation of the vertical semicircular canals in 16 dwarf parrots. Pre- and
post-habituation stimuli were accelerations and decelerations of 10°/sec.? for 12 sec., separated by 2 min. of constant
velocity. Habituation stintuli were accelerations of 10°/sec.? for 12 sec. (decelerations were subthreshold).

Pre-1 and post-1

Dwarf parrots (accel. and decel.)

Habituation series
(15 trials: accel. only)

Pre-2 and post-2
(accel. and decel.)

CW—beak down
CW—beak up
CCW—beak down

CCW—beak up

CW—beak down

CW—beak up
CCW—beak down
CCW—beak up

CW—beak down
CW—beak up
CCW—beak down

CCW—beak up

CW—beak down
CW—beak up
CCW—beak down

CCW beak up

CW—beak up

CW—beak down Al CW
CCOW—beak up (beak down)
CCW—beak down

CW—beak up

CW—beak down AL CW
CCOW—pbeak up (beak up)
CCW—beak down

CW —beak up

CW—beak down All CCW
CCW—beak up (beak down)
CCW—beak down

CW —beak up

CW—beak down Al COW
CCW—beak up (beak up)

CCW—beak down

Scoring. Measurements were made of slow-
phase eye displacement, frequency of nystagmus,
and duration of response as outlined elsewhere.**
For the African parrots, it was possible to con-
vert the horizontal slow-phase measurements to
degrees of eye movement by means of a calibra--
tion factor obtained from the birds’ responses to
optokinetic stimulation.* Vertical eye move-
ments could be obtained only occasionally from
a few of the dwarf parrots exposed to the opto-
kinetic stimulator, hence slow-phase measure-
ments of their vertical eye movements were
expressed in arbitrary units.

III. Results and Discussion.

Stimulation of the lateral canals. A sample
of the tracings of horizontal eye movements ob-

tained from one of the African parrots appears
in Figure 1. Mean response scores for the six
birds for measures of slow-phase displacement,
frequency, and duration of nystagmus from the
right eye are presented in Table 3 and depicted
in Figure 2.

For the direction of nystagmus repeatedly
elicited during habituation trials, there was a
decline for all three measures (relative change
scores) from the pre-test to post-1; the decline
was statistically significant for slow-phase
(t=5.38, p<.01) and frequency (t=1147,
p<.001) measures, but not for duration (t=1.36,
p<.05 level=2.57). The unhabituated direction
of nystagmus showed some decline from the
pre-test to post-1 (except for an increase in the



NYSTAGMUS
HABITUATED DIRECTION

PRE peer ermirypryyanyn e e

POST

UNHABITUATED DIRECTION
PRE [eA ennnnnndian ath tet .
AR aannne SR

POST

Wey NR RUINS

NOILISOd GW3H
Q3LVNLIGVH

HABITUATED DIRECTION

PRE — [A aay ren ee

POST

Amn AL
UNHABITUATED DIRECTION

PRE {Na a UR

NOILISOd OV3H
Q3.LVNLIGVHNN

post fl Mair anata tet

PARROT 12

Ficure 3. Tracings of vertical nystagmus obtained from a dwarf parrot.
tained for this bird. Vertical bars demarcate stimulus periods of 10°/sec.? for 15 sec.
deflections of the recording pen signify vertical eye movements in those same directions,
rectional habituation trials occurred between the pre-test and post-tests.
the head position used and for the direction repeatedly elicited during the habituation series,

That same direction of nystagmus is considerably enhanced

secondary nystagmus in the topmost post-tracing.)

“Le
30°

2 sec

An optokinetic calibration was ob-
Upward and downward

A series of 15 unidi-
Nystagmus declined significantly for
(Note the early

during the post-test trial for the unhabituated head position.

erated by the semicircular canals, the otoliths,
and other gravi-receptors interact to a consider-
able degree in determining habituation of nys-
tagmus in some animals. This proposed inter-
action would thus be more dynamic than the
previously reported regulatory effects (ie., in-
hibiting or enhancing responses) of the otoliths
on semicircular canal activity.

IV. Summary.

Horizontal ocular nystagmus from restrained
birds was habituated in a directionally specific

fashion by means of repeated angular accelera-
tions. Substantial response recovery was evident
following 2 weeks of rest. Vertical nystagmus was
similarly habituated in a separate group of birds.
The reduction of the latter response was ob-
tained with the birds positioned so that vertical
semicircular canals were in the plane of rotation.
By changing the position of the birds 180° after
the habituation trials, the same set of canals
could be stimulated but with the otoliths and
other gravi-receptors oriented differently. Hab-
ituation was relatively specific for the direction


‘Tarim 3.—Mean horizontal slow-phase eye displacement, number of nystagmic beats, and response duration obtained
from six African parrots during tests before and after a series of 15 unidirectional angular accelerations. Data represent
an average of two trials per subject (CW accel. and CCW decel., or CW decel. and CCW aceel.). The lateral canals
were in the plane of rotation. All responses were recorded from the right eye of each bird. Pre-test and post-1 tests,
respectively, were given immediately before and after the habituation series; post-2 tests were conducted 2 weeks

later.

Habituated direction

Test Slow-phase Frequency Duration
Degrees — % of pre- Beats % of pre- | Seconds  % of pre-
469.3 _----------- 35.6 .-----------| 25.8 ------------
253.7 54.1 19.2 53.9 23.1 89.5
410.5 87.5 31.9 89.6 26.1 101.2
Unhabituated direction
Slow-phase Frequency Duration
Test
Degrees —% of pre- Beats % ot pre- | Seconds —% of pre-
472.3 _-.--------- 36.7 ------------| 25.8 ---.--.-----
404.1 85.6 33.8 92.1 28.3 109.7
405.6 85.9 32.1 87.5 25.8 100.0

Tanz 4.—Results of t tests between pre-test and post-
test scores for the habituated and the unhabituated
direction of nystagmus.

Direction of nystagmus

Measure Comparisons

Habituated | Unha-

bituated

Slow-phase__| Pre- vs. post-1 #5, 38 1.76
Pre- vs. post-2 2.33 #4, 40
Post-1 vs. post-2 *3.35 0,04

Frequeney...| Pre- vs. post-2 +L AT 2.43
Pre-vs. post-2 0.70 2.21
Post-1 vs. post-2 #3.90 0.66
Duration__..| Pre- vs. post-1 1.36 1.98
Pre- vs. post-2 0.61 0.53
Post-1 vs. post-2 1,36 174

Levels of significance: *—.05, **—.01, ***—.001

in Figure 38. Mean response scores for duration,
frequency, and slow-phase eye displacement, for
each of the two head positions, appear in Table 6
and are graphically presented in Figure 4.

Statistical analyses (Table 7) of pre- and post-
test scores indicate that nystagmus in the direc-
tion repeatedly elicited during habituation trials
declined significantly for all three response
measures when the birds were maintained in the
same position as that imposed during the hab-
ituation series, For a change in position of 180°,
however, only frequency of nystagmus showed
a significant pre- to post-test decline (see Figure
4 and Table 7).

Statistical comparisons of the relative change
of post-test scores from those of the pre-test
appear in Table 8. The decline in nystagmic
output for the habituated direction and the head-
body position used during the habituation series
was significantly greater (.05-~.01 levels) than
the pre- to post-test changes for either direction
of nystagmus in the unhabituated head position,



PARROT 5 (HORIZONTAL NYSTAGMUS)

PRE LIAN arcnletabagynnhnnnnnnnrn
POST-I pe RR RR

POST-2

cw ACCEL:

PRE

5°/SEC® for 12 SEC

eee nnn

40°

POST-| fa AAV OULAALE. Wanrnrreeu

POST-2 fo Ne epee 40°]

- ccw ACCEL:

Fieve 1, ‘Tracings obtained from an African parrot.
markers appear to the right of the tracings.

5°/SEC? for 12 SEC

Vertical bars demarcate the stimulus periods; calibration
Upward deflections of the recording pen signify eye movements
to the right; downward deflections signify eye movements to the left.

A series of 15 unidirectional habitua-

tion trials occurred between the pre-test and post-1 tests; post-2 tests were given 2 weeks later. A clear, direc-
tionally specific reduction is evident in the post-1 tracings (CW acceleration), with a strong recovery from

habituation apparent in the post-2 data.

average duration score), but the declines were
not significant. Post-2 tests, conducted 2 weeks
later, showed recovery of the habituated response.
Nystagmus in the unhabituated direction was
approximately at the same level in the post-1
and post-2 sessions, but the latter tested as sig-
nificantly lower than the pre-test (t=4.40,
p<.01), due to the fact that all six parrots
showed some decline from the pre-test to post-2
(see Table 4).

Comparisons among relative change scores ap-
pear in Table 5. The declines of slow-phase eye
movement and frequency of nystagmus in the
habituated direction from the pre-test to post-1

were significantly greater than both the pre- to
post-1 change for the unhabituated direction, and
the pre- to post-2 change for the habituated
direction. No other comparisons produced sta-
tistically significant differences.

Thus, ocular nystagmus from parrots under-
went relatively rapid habituation and the re-
sponse decline was (relatively) directionally
specific. Considerable recovery occurred follow-
ing a 2-week rest. These results are similar to
those obtained from other animals,°-* 7

Stimulation of the vertical canals. Tracings
of the vertical component of eye movements re-
corded from one eye of a dwarf parrot appear


Taste 6.—Mean vertical slow-phase eye displacement,

number of nystagmic beats and response duration during pre-

and post-habituation trials for 16 dwarf parrots. Data for both the habituated and unhabituated directions of

nystagmus are presented for the head position used during the 15 habituation trials and for a 180°

position (‘unhabituated head position’”’).

change in head

Habituated head position: Unhabituated head position:
Direction of nystagmus Direction of nystagmus
Measure Test
Habituated Unhabituated Habituated Unhabituated

Slow-phase Pre 148.0 172.3 165.0 160. 6
(Arbitrary Units) Post 99.4 181.4 227.7 162. 0
Number of Beats..--.--- Pre 34.1 32.2 34.3 27.7
Post. 17.5 28.8 26.9 26.3

Duration (Seconds). -..-- Pre 23.1 22.1 22.5 21.4
Post: 18.0 22.1 QL 20.4

as well as for the unpracticed direction of nys-
tagmus in the habituated head-body position.
No other comparisons yielded statistically sig-
nificant differences (see Table 8 and Figure 4).
Thus, habituation of vertical ocular nystagmus
occurred in the birds and was confined to the
direction repeatedly elicited. Moreover, the re-
duction in response was relatively specific to the
position maintained by the animals during the
habituation series, i.e., there was relatively little
or no transfer of habituation when the same
canals were stimulated but with the position of
the animals changed by 180°. These data agree
with related results obtained from cats,’ and do
not appear to be due to arousal factors caused
by changing the position of the animals. In
addition to the auditory stimuli used to help
maintain arousal during response periods, several

birds were given six or more additional trials in
the “unpracticed” head-body position; the re-
sponse declined in the usual fashion. The birds
were then placed in the opposite position (that.
maintained during the original habituation
series) ; no recovery of response from the post-1
levels was apparent. Further trials involved
alternating the position of the animals. No
discernible effects of the handling occurred.

The results permit two interpretations: (1) The
specificity of the response reduction is due to
factors generally associated with the habituation
procedure, ie. the animal becomes habituated to
the general environment as well as to the ac-
celeration stimulus, and “significant” changes in
the environment (including body position) re-
sult in a failure of habituation to transfer to the
new situation and; (2) the neural patterns gen-

TapLe 7.—Results of t tests between pre- and post-test scores for the two directions of nystagmus and the two head-body

positions.
Condition t
Direetion of nystagmus Head position Slow-phase Frequency Duration
Habituated Habituated ¥2.72 m4 OA **3,08
Habituated Unhabituated 1,67 #2, 58 0,98,
Unhabituated Habituated 0.41 1,60 0.00
Unhabituated Unhabituated 0.08 1.05 1.31

Levels of significance: *—.05, **—-.01, ***—.001



AM 69-20

ADAPTATION TO VESTIBULAR DISORIENTATION: XI.

THE INFLUENCE OF SPECIFIC AND NONSPECIFIC
GRAVI-RECEPTORS ON NYSTAGMIC RESPONSES
TO ANGULAR ACCELERATION

William E. Collins, Ph.D.
Billy P. Updegraff, B.S.

Approved by Released by
J. Roserr Diniz, M.D. P. V. Sern, M.D.
Cuter, Crviz AEROMEDICAL Feperat Arr Surczon
Insrrrute

October 1969

Department of Transportation

FEDERAL AVIATION ADMINISTRATION
Office of Aviation Medicine



e

rs

Pa

e

na

2

10.

11,

. Commins, W.

REFERENCES

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the vestibular caloric test. Acta Otolaryngologica

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. Capps, M. J., and Cottins, W. E.: Effects of bilateral

caloric habituation on vestibular nystagmus in the
cat. Acta Otolaryngologica (Stockh.), 59 :511-530,
1965,

Cottins, W. E,: Nystagmus responses of the cat to
rotation and to directionally equivalent and non-
equivalent stimuli after unilateral caloric habitua-
tion, Acta Otolaryngologica (Stockh.), 58 :247-258,
1964.

. Commins, W. E.: Primary, secondary, and caloric

nystagmus of the cat following habituation to rota-
tion, Journal of Comparative and Physiological
Psychology. 57 :417-421, 1964.

E.: Influence of head position on the
habituation of vertical vestibular nystagmus in the
cat. Journal of Comparative and Physiological
Psychology. 67 :156-159, 1969.

Cortins, W. E., and Hurrmay, H. W.: Design and
performance characteristics of a mechanically driven
vestibular stimulator. FAA CARI Report No. 64-15,
Oklahoma City, Oklahoma, 1964.

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

. GuEDRY, F, E.: Habituation to complex vestibular

stimulation in man: Transfer and retention of ef-
fects from 12 days of rotation at 10 r.p.m. Percep-
tual and Motor Skills, 21:459-481, 1965,

Guepry, F. E.: Influence of linear and angular ac-
celerations on nystagmus. In: Second Symposium
on the Role of the Vestibular Organs in Space Bx-
ploration, NASA Report No. SP-115, 185-198, 1966.
Guepry, F. EB, Counns, W. E., and Gravsrer, A.:
Vestibular habituation during repetitive complex
stimulation: A study of transfer effects, Journal of
Applied Physiology, 19 :1005-1015, 1964.

Jonexrrs, L. B. W., and Puripszoon, A. J.: Nys-
tagmus provoked by linear accelerations. Acta

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. MERTENS,

Physiologica et Pharmacologica Neerlandica, 10 :239-
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Jonaxees, L, B. W., and Purtrpszoon, A. J.: The
influence of position upon the eye-movements pro-
voked by linear accelerations. Acta Otolaryngologica
(Stockh.), 56:414-419, 1963.

Jonaxegs, L, B, W., and Puitipszoon, A. J.: Electro-
nystagmography. Acta Otolaryngologica (Stockh.),
Suppl. 189, 1-109, 1964.

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

R. A. and Cottins, W. E.: Unilateral
caloric habituation of nystagmus in the cat: Effects
on rotational and bilateral caloric responses, Acta
Otolaryngologica (Stockh.), 64 :281-297, 1967.

Niven, J. L, Hixson, W. C., and Correa, M. J.: An
experimental approach to the dynamics of the ves-
tibular mechanisms. In: Symposium on the Role
of the Vestibular Organs in the Exploration of
Space, NASA Report No. SP-77, 48-56, 1965.

Owapa, K., and Oxuno, K.: The ofolithic reaction
on nystagmus by caloric stimulations, In: Contribu-
tion to the Vestibular Physiology and Vestibular
Test (Japan society of vestibular research), Acta
Otolaryngologica (Stockh.), Suppl. 179, 1-6, 1963,

Putuipszoon, A, J,: Some experiments on the func-
tion of the labyrinth: I, Practica Oto-rhino-laryn-
gologica, 24 :344-347, 1962.

Winer, C. M. and Sairx, A. H.: Quantitative
measurement of the labyrinthine function in the
fowl by nystagmography. Journal of Applied
Physiology, 17:712-718, 1962.

Wineer, C. M, Sarrn, A, H., and Kerry, ©. F.:
Effects of chronic acceleration on induced nystagmus
in the fowl. Journal of Applied Physiology, 17 :709-
711, 1962.


of nystagmus repeatedly elicited and for the
head and body position maintained during hab-

gravi-receptors and the semicircular canals is
suggested as a possible feature of nystagmic

ituation trials. A dynamic interaction between habituation.
140 - r r
sol HABITUATED UNHABITUATED
r HEAD POSITION HEAD POSITION
veo b [ | DIRECTION oF nvsTaGMuS
ws + HaprTuATED a---0
Zz Nor r = ©-——© UNHABITUATED 4--~4
$ N=I6
@ 100 r a r
G wor Sos, ae
© sol L \ =
‘ \
Gop t \
is)
o& 70h b L
Ww
a L NUMBER OF
SLOW-PHASE NYSTAGMUS EYE MOVEMENTS - DURATION OF NYSTAGMUS
sob L |
L L L 1 L 1 1 4 1 L ps
PRE POST PRE POST. PRE POST. PRE POST PRE POST PRE POST
HABITUATED UNHABITUATEO HaBITUATED UNHABITUATED HABITUATED UNHABITUATED
HEAD POSITION HEAD POSITION HEAD POSITION HEAD POSITION HEAD POSITION HEAD POSITION
TRIALS

Ficure 4. Mean change (in percent) of post-test scores from pre-test levels for three measures of vertical nystagmus

obtained from dwarf parrots.

Pre-test scores for the habituated and the unhabituated directions of nystagmus

were each set at 100 percent. Response reduction is directionally specific and relatively specific to the head po-

sition used during the habituation series,

‘TaBuE 8.—Results of t tests on relative change scores (pre- to post-test) between the various combinations of head-body
position and direction of nystagmus (Hab=Habituated; Unhab=Unhabituated). The pre- to post-test decline
for the habituated direction of nystagmus in the habituated head position was significantly greater than the
pre- to post-test changes obtained for other head-position and nystagmus-direction combinations.

Comparisons t
Head Nystagmus Head | Nystagmus | — Slow- Number
position direction vs. position | direction phase of beats | Duration
Hab Hab vs. Hab Unhab 43,42 93,04 #256
Hab Hab vs. Unhab Unhab 2,34 45,47 1.53
Hab Hab vs. Unhab Hab 43,26 *#3,10 1.51
Hab Unhab vs. Unhab Hab 0.69 1.13 1.10
Hab Unhab vs. Unhab Unhab 0.46 0.53 1.44
Unhab Unhab vs. Unhab Hab 1,35 0.90 0.05

Levels of significance: *.05, **~.01.



HO - r r

1oo F L
90F L
W gob L
80
ral
ig 70 bE
rH]
a SP DIRECTION OF NYSTAGMUS
& sob L [|| @——e HABITUATED
a o-——0 UNHABITUATED
© ak L L Ne6
iv
# sob i. L
20 | SLOW-PHASE NYSTAGMUS NUMBER OF EYE MOVEMENTS [- DURATION OF NYSTAGMUS.
tob L L
n L J 1 \ \ L L _
PRE POST-I POST-2 PRE POST-I POST-2 - PRE POST-I POST-2
TRIALS

Figure 2, Mean change (in percent) of post-1 and post-2 scores from pre-test levels for three measures of hori-
zontal nystagmus obtained from African parrots, Pre-test scores for the habituated and the unhabituated
directions were each set at 100 percent. Directionally specific effects of the habituation series (post-1) are
marked, and recovery (post-2) is clearly evident.

Taste 5.—Results of t tests comparing the relative
change in post-1 and post-2 responses from those of the
pre-test for the habituated and the unhabituated direc-
tions of nystagmus.

Comparisons of relative change Measure t
Habituated: Pre- to post-1 Slow-phase 43.38
vs. Frequency +3.70
Habituated: Pre- to post-2 Duration 1,38
Habituated: Pre- to post-2 Slow-phase *#4,18
vs. Frequency **#10. 46
Unhabituated: Pre- to post-1_ Duration 1,93
Unhabituated: Pre- to post-1 __ Slow-phase 1,02
vs. Frequency 0. 60
Unhabituated: Pre- to post-2 Duration 1.71
Unhabituated: Pre- to post-2 _ Slow-phase 0.36
vs. Frequney 0.72
Habituated: Pre- to post-2 Duration 0.95

Levels of significance: *—-.05, **—.01, ***—,001

6


complete immobilization of the subject. Needle
electrodes were inserted on each side of each eye
of the African parrots, and above and below each
eye of the dwarf parrots so that separate record-
ings of either horizontal or vertical components
of nystagmus were obtained from the right and
left eye of each bird. Recording from both eyes
separately but simultaneously permitted a choice
of tracings for scoring and provided additional
assurance that a complete set of tracings would
be obtained even though a recording problem
(eg., a pulled electrode) might develop. The
recorder was an Offner Type R Dynograph with
3 sec. time constants. Animals were tested in
groups of two or three by means of a tier ar-
rangement on the Huffman Rotation Device.*?
A variety of auditory stimuli was presented
during response periods to help maintain alert-
ness in the birds.

African parrots: Lateral-canal stimulation.
African parrots were tested with their lateral
canals in the plane of rotation and with their
heads (and bodies) positioned over the turning
axis of the rotator. Two pre- and two post-
habituation trials, immediately preceding or
following the habituation series, were conducted
as indicated in Table 1; stimuli comprised ac-
celerations and decelerations of 5°/sec.? for 12
sec., separated by 2 min. of constant velocity.
The habituation series comprised 15 accelerations
of 5°/sec.? for 12 sec., followed by 1 min. of
constant velocity and subthreshold decelerations
(0.15°/sec.? for 400 sec.), An additional pair
of post-tests, conducted 2 weeks after the initial
pair, examined the question of retention of
habituation. All trials were in total darkness;
rest intervals between trials (i.e., with the rotator
at a standstill) were from 3 to 5 minutes in room
illumination.

Taste 1.—Outline of test procedure for stimulation of the lateral semicircular canals in six African parrots. Pre- and.
post-habituation stimuli were accelerations and decelerations of 5°/sec.? for 12 sec., separated by 2 min. of constant
velocity. Habituation stimuli comprised accelerations of 5°/sec.? for 12 sec. (decelerations were subthreshold)

Pre-trails
(accel. and decel.)
African parrots

Post-trials
Habituation series (accel. and decel.)

(15 trials; accel. only)

1 2 1 2
Acl, A-2, A-Bo 222222 eee ee ow cow cw cw cow
And, A+B, A-6.2 222222222 cow ow cw cow cw

Dwarf parrots: Vertical-canal stimulation. In
the major portion of the study, dwarf parrots
were placed in a tilted position with their heads
over the axis of rotation. Two body placements
were used: “beak down” and “beak up.” For the
“beak down” position, the container holding the
birds was tilted 90° forward and approximately
45° to the left of the birds (from the restrained,
upright position) ; the “beak up” position repre-
sented a change of 180° from “beak down.” In
these positions, a brisk vertical nystagmus could
be elicited. By visual observation of birds used
in pilot studies, the direction of the eye-movement
responses tended to be somewhat oblique and the
direction of the fast-phase in one eye was oppo-
site to that of the other eye.

The 16 dwarf parrots were divided into four
groups according to body placement and to di-
rection of rotation during habituation trials (see
Table 2). Thus, two groups received habituation
trials in a “beak down” position; one with CW
(clockwise) and the other with CCW (counter-
clockwise) rotation. The remaining two groups
were habituated with “beaks up,” one during
CW and the other during CCW rotation. The
habituation series for all birds comprised 15
accelerations of 10°/sec.? for 12 sec.; each ac-
celeration was followed by 1 min. at constant
velocity and a subthreshold deceleration (0.15°/
sec.? for 800 sec.). Two pre- and two post-tests
were conducted immediately before and imme-
diately after the habituation series. Within each


ADAPTATION TO VESTIBULAR DISORIENTATION: XI.
THE INFLUENCE OF SPECIFIC AND NONSPECIFIC GRAVI-RECEPTORS
ON NYSTAGMIC RESPONSES TO ANGULAR ACCELERATION

I. Introduction.

During aircraft maneuvers, pilots frequently
experience combined linear and angular accelera-
tions. That such combination might modify the
responses ordinarily identified with one or the
other stimulus has been suggested by several re-
cent investigations. These studies have cited the
possible influences of nonspecific and specific
gravi-receptors, particularly the otoliths (de-
tectors of linear acceleration), on reactions
usually attributed solely to the activity of the
semicircular canals (detectors of angular accelera-
tion). Thus, the failure of habituation of ves-
tibular responses to transfer from one stimulus
modality (e.g., caloric) to another (e.g., rotation)
in cats?*45 and from one quadrant of head
movements to another in human coriolis studies,? °
has been attributed to possible differences in the
pattern of stimulation contributed from several
sources including the otoliths. Data obtained
from rabbits which had undergone nerve resec-
tions led Owada and Okubo’ to conclude that
the otoliths exert some regulatory functions on
nystagmus, while studies with centrifuges showed
that otolithic stimulation influenced the magni-
tude of nystagmus obtained from humans as a
result of both calorizations' and angular accelera-
tions.* Linear accelerations produced by parallel
swings have caused nystagmus in humans and
rabbits when the eyes of the subjects were devi-
ated laterally*#**** and horizontal nystagmic
reactions have been reported for humans exposed
to periodic linear accelerations.’* Additionally,

‘The animals used for this experiment were lawfully
acquired and treated in accordance with the “Principles
of Laboratory Animal Care” issued by the Animal Fa-
cilities Standards Committee of the Animal Care Panel,
United States Department of Health, Education, and
Welfare, Public Health Service, March 1963. We grate-
fully acknowledge assistance rendered by Sue Downs
Brown and Nancy Rice during the conduct of this study.

the augmentation or reduction of nystagmus
during rotation of human subjects about an
earth-horizontal axis was attributed by Guedry®
to the changing location of the gravity vector.

Collins® examined the possible influence of
gravi-receptors on habituation of nystagmus in
cats. Cats placed on their sides were given a
series of angular accelerations which significantly
reduced their nystagmic reaction. However,
when the position of each cat was changed by
180° (thereby keeping the same sets of canals in
the plane of rotation), no habituation effects were
apparent during subsequent testing.

With few exceptions,® 1 *° studies of vestibu-
lar habituation in birds have been concerned with
head nystagmus rather than with ocular responses
to stimulation of the semicircular canals. The
present study was designed to examine the pro-
cess of habituation of ocular nystagmus in birds
and to explore further the possibility of an inter-
action between gravi-receptors and semicircular
canal activity in the habituation process.

II. Method.

Subjects. Habituation of horizontal nystag-
mus was examined in a group of six African
parrots. Sixteen dwarf parrots were used to
examine the influence of the position of specific
and nonspecific gravi-receptors on the habitua-
tion of vertical nystagmus. Each bird was re-
strained by means of a band of gauze which
served both to keep the wings against the body
and to secure a special arched, cloth-covered
brace which extended from the back of the bird
around the top of its head. ‘The beak of the bird
was taped closed and secured (in approximately
the position of normal carriage relative to the
bird’s body) to the edge of a metal container in
which the bird was placed. Additional tape ex-
tended across the cloth-covered brace from one
side of the container to the other and provided



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