MANIPULATION OF AROUSAL AND ITS EFFECTS ON HUMAN 

VESTIBULAR NYSTAGMUS INDUCED BY CALORIC IRRIGATION 

AND ANGULAR ACCELERATIONS 

WILLIAM E. COLLINS, PH. D. 

Sensory Psychology Section 

Psychology Branch 

62-17 

FEDERAL AVIATION AGENCY 

AVIATION MEDICAL SERVICE 

AEROMEDICAL RESEARCH DIVISON 

CIVIL AEROMEDICAL RESEARCH INSTITUTE 

OKLAHOMA CITY, OKLAHOMA 

OCTOBER 1962 
MANIPULATION OF AROUSAL AND ITS EFFECTS ON HUMAN 

VESTIBULAR NYSTAGMUS INDUCED BY CALORIC IRRIGATION 

AND ANGULAR ACCELERATIONS 0 

WILLIAM E. COLLINS, PH.D. 

INTRODUCTION 

Alterations in the nystagmic reaction of human subjects exposed to vestibular stimulation 

have been frequently noted in studies of drug effects, •· 5, 25, 20 , 33 "habituation", ••. ••· u, 11, 2s, s 6, 37 

and general features of the labyrinthine response. '· •· 3, 21, 27, ••· 31, 35 Wendt 36, 37 has maintained that, when visual stimuli are excluded, 

the primary source of intra-subject variability is 

the orientation of the subject. Specifically, 

Wendt has held that a brisk vestibular nystagmus is obtained so long as the subject remains 

"environment-directed" and does not lapse into 

a "reverie" attitude. 

The present report represents a compilation 

of the results of several experiments in which 

methods of controlling the psychological attitude of the subject were evaluated. Control 

features were then introduced in the examination of some basic theoretical and applied 

aspects of the vestibular response. 

•Report presented at the annual meeting of the Aerospace 

Medical Association, Atlantic City, New Jersey, April 9, 

1962. The studies were conducted at the U.S. Army 

Medical Research Laboratory, Fort Knox, Kentucky. The 

technical assistance of Kenneth J. Gall is gratefully acknowledged. 

APPARATUS AND PROCEDURE 

Angular Accelerations. The rotary appara

was a turntable •o situated in a light-proof roo

Subjects were seated upright at the center 

the device and a bite-board positioned th

heads so that the horizontal semi-circular can

were in the plane of rotation. 

In all cases, an acceleration was preceded 

30 seconds of rotation, and a deceleration w

followed by 60 seconds of rotation, at a co

stant velocity of 1: rpm. All trials were co

ducted in total darkness. The various accele

tion schedules employed appear in Table 1

Caloric Stimulation. Caloric studies we

conducted in a shielded, light-proof room. T

testing apparatus consisted of a padded ste

bed with adjustable head-section, a water ba

with attached tubing terminating in a glass e

insert, and a pan to collect the return flo

from the ear. The bed was adjusted so th

the head was elevated 30° from the supi

position. Trials consisted of 40 seconds 

irrigation with water at 30° C. Administrati

of the stimulus took place, in all cases, wi

the room illuminated. Sixteen subjects 

"naive" and 8 "experienced") were given 

trials each. The fifth trial, in all cases, involv

room illumination and gaze-fixation on a ceili

-1-
TABLE 1 

Outline of the stimulus conditions employed. Instructions included mental arithmetic (MA), 

Reverie ( REV) , signalling subjective velocity by key presses ( KP), temporal reproduction 

(REPRO) and attending to the sensation of rotation ( ATS ). 

Rotatory Conditions 

Constant Constant Constant 

Velocity Accel. Velocity Decel. Velocity Instructions 

Value 1 rpm 4.5° / sec• 12.2 rpm 4.So /sec• 1 rpm MA, REV, 

Duration 30 sec 15 sec 120 sec 15 sec 60 sec KP,REPRO 

Value 1 rpm 4.1 ° / sec• 10 rpm 4.1° /sec• 1 rpm MA and 

Duration 30 sec 13 sec 100 sec 13 sec 60 sec REV 

Value 1 rpm 1.8° /sec• 16 rpm 1.8° / sec' 1 rpm MA and 

Duration 30 sec 50 sec 120 sec 50 sec 60 sec ATS 

Value 1 rpm 1.0° / sec• 15 rpm 1.0° /sec• 1 rpm MAand 

Duration 30 sec 84 sec 120 sec 84 sec 60 sec ATS 

Value 1 rpm 0.5° /sec• 10.2 rpm 0.5° /sec• 1 rpm MAand 

Duration .10 set· 110 sec 120 sec 110 sec 60 sec ATS 

Caloric Conditions 

Four subjects were tt•sted according to each trial sequence. 

1"rial Fixation Sequence 

Identification Distance Environment Instruction of Triols 

1 .30.5 em Illumination REV A-1,2,3,4,5 

2 Darkness REV B-2, 1,4,3,5 

3 30.5 em Illumination MA C-3, 4, 1, 2, 5 

4 Darkness MA D-4, 3, 2, 1, 5 

5 1.63 m Illumination MA 

mark. A counterbalanced order of presentation 

was established for the first 4 trials, such that 

2 subjects from each group were tested according to each sequence. Two of these trials were 

in room illumination with fixation on a small 

target 30.5 em from the subject. For the remaining two trials, all lights were extinguished 

at the moment of stimulus termination. An 

outline of the caloric test conditions appears 

in Table 1. · 

In addition to the recording of nystagmus 

tracings, the duration of response in illumination was timed by the investigator by direct 

observation. A qualitative rating on a 0-4 scale 

of the observed regularity, frequency, and 

amplitude of response was also made. The 

timer-rater was never aware of the instructions 

given to the subjects. 

Nystagmus Recordings. Horizontal compo

ents of nystagmus and periods of stimulati

were recorded on an Offner Type-T Electr

encephalograph. Electrodes were taped at t

outer canthus of each eye and an indiffere

electrode was taped on the mastoid proce

Prior to each trial, calibration data relating d

grees of eye movement to pen deflection we

obtained. 

Instructions. In all cases, subjects were to

to keep their eyes open and, in darkness, 

stare "straight ahead." Several sets of instru

tions were designed in an effort to influen

the states of alertness or arousal of the subjec

throughout a given trial, and thereby provi

some control of the subject's "orientation." Tw

of these, mental arithmetic and reverie, prov

-2-
particularly effective and were employed in 

most of the experiments conducted. The instructions included: 

1) Mental Arithmetic (MA)-Subjects were 

given a starting dividend and a constant divisor. 

They were told to divide silently and continuously throughout a given trial, using each 

successive quotient as the next dividend. It 

was emphasized that the arithmetic process 

should begin promptly at a given signal ( 10 

seconds prior to acceleration and 30 seconds 

prior to termination of calorization) and should 

continue with a maximum effort at speed and 

accuracy until the conclusion of the trial. The 

task assumed the nature of a challenge and 

subjects expressed interest in their speed an<;l 

accuracy as compared with others. All answers 

were recorded at the conclusion of a trial. 

2) Reverie (REV)-Subjects were instructed 

to ignore the stimulus environment, to relax 

and daydream, but to keep their eyes open. 

They were requested not to pursue any particular line of thought. 

3) Key Pressing (KP)-A telegraph key, connected to the recorder, was secured to the arm 

of the turntable chair. Each subject was instructed to attend to the sensation of rotation 

and to indicate, by pressing the key, the onset, 

cessation, and each experience of 90° of subjective rotation. 

4) Temporal Reproduction (REPRO)-A 

buzzer was connected to the telegraph key and 

to an outside control. Sound stimuli were 

systematically presented throughout a given 

trial for durations varying between 0.5 and 6.5 

seconds. Subjects were instructed to atte

carefully to the onset of the sound and, at 

conclusion, to reproduce its duration by pre

ing the telegraph key. 

5) Attend to Sensation (ATS)-Subjects we

instructed to attend carefully to the rotato

sensations produced by acceleration. Th

were to report verbally on intensity, duratio

and direction of experienced rotation at t

conclusion of a trial. 

RESULTS AND DISCUSSION 

Angular Accelerations 

A. GENERAL EFFECTS oF AssiGNED TASK. 

The effects of four assigned tasks ( MA, RE

KP, and REPRO) on nystagmus responses 

a 4.5° j sec• angular acceleration (see Table 

were examined." Data were recorded from 

subjects. Each subject was given 6 trials p

day for 4 consecutive days. A single task w

assigned to a subject on a given day, but t

order of task-presentation differed systema

cally among subjects. The following resu

were obtained: 

1. Both amplitude and duration of t

nystagmic response were affected 

instructions. 

2. Mental arithmetic was the most effica

ous means of maintaining a brisk, lon

duration nystagmus. 

3. Reverie states produced the most varia

nystagmus responses. In some cases, 

nystagmic beats were detected. 

TABLE 2 

The average slow-phase velocity of nystagmus for 30-second periods beginning with the onset 

of the stimulus and the average total duration of response under 4 instruction-conditions (mental 

arithmetic, key pressing, temporal reproduction, and reverie ). Data are averages of 6 accelerations, 6 decelerations, and 8 subjects (stimulus: 4.5°/sec2 for 15 seconds). 

Task 

MA 

KP 

REPRO 

REV 

Average Slow-Phase 

Velodty (Deg/ Sec) 

for first 30 Sec 

18.7 

16.3 

14.5 

8.1 

-3-

Average Total 

Nystagmus Duration (Sec) 

47.0 

41.0 

38.6 

26.7 
u ~ 

CD ~ 

~ 25 rOt 

CD ~ 

e ~ 

r-

> 20 r-

!::: ~ 0 

9 

l&J 

> 15 

CJ) 

::::> 

(!) 

~ - ~ 10 

CJ) 

> z - l&J 

CJ) 5 <t 

:I: 

a.. I 

~ 

0 

MA ·--· 

REV o---0 

STIMULUS 

• 

_j_ + 

..J 

CJ) 0 10 20 30 40 50 60 70 

TIME IN SECONDS 

FIGURE 1. Average slow-phase eye velocity ( deg/ sec) for 5-second intervals under conditions 

of mental arithmetic ( MA) and reverie (REV). Data are averages for 8 subjects, each 

given 6 accelerations and 6 decelerations under each condition. Arrow indicates point of 

stimulus termination ( 4.5° /sec• for 15 seconds). 

The average duration of nystagmus for the 

group and the average slow-phase velocity for 

30-second periods beginning with stimulus onset 

appear in Table 2. The importance of arousal 

or alertness level in the evaluation of vestibular 

responses is clearly evident. As Wendt 36

' 

37 has 

noted, reverie states result in a decline or 

abolishment of nystagmus (see Figs. 1 and 2). 

The maintenance of an alert state, by simple 

instructions outlining subject-tasks, tends to 

prevent such declines and probably permits a 

more accurate evaluation of the vestibular 

response. 

The tasks, however, differ in efficiency in 

maintaining nystagmus. Mental arithmetic consistently yielded brisk, long-duration responses. 

The key-pressing condition, a measure of subjective velocity,'" appeared reasonably effectiv

but, since the subjective experience of rotatio

tends to decline with repeated stimulation, 18 

consequent reduction of nystagmus also prob

ably occurs as the subject's attention is less an

less required."1 The REPRO instructions wer

generally effective especially in early trials

However, in later trials for some subjects

nystagmus occasionally became less wel

defined. It is known that timing behavior ca

become quite automatic (subjects can be con

ditioned to respond with timing behavior dur

ing sleep) and, as mental effort declines

nystagmus is similarly affected. Reverie state

probably differ little from those of uninstructe

subjects or of subjects who are assigned some

what vague tasks. 

-4-
SUBJECT 8 DECELERATION 

SESSION I- REVERIE 

TRIAL I 

SESSION ll -REPRODUCTION 

TRIAL 2 

TRIALS 

FIGURE 2. Nystagmus recordings from deceleration trials for a single subject under conditions of reverie and temporal reproduction. Vertical bars through the records denote the 

stimulus periods ( 4.5 ° I sec2 for 15 seconds) . Calibration markers at the right of each 

record indicate 20° eye excursions. Note the less well-defined eye movements in Reproduction trials 5 and 6. Mental arithmetic trials (not depicted here) consistently yielded vigorous, 

well-defined nystagmus as in Reproduction trial 2. 

B. SPECIAL EFFECTs oF AssiGNED TASKS. 

1. Responses after administration of an analeptic. Many early reports noted the fact that 

something like alertness exerted an influence on 

nystagmus production. Mowrer30 with pigeons, 

Griffith17 and Pearcy and Hayden31 with normal 

humans, and Angyal and Blackman• with schizophrenics noted effects due to "excitement" or 

levels of physical tension. More recently, 

Crampton" and Crampton and Schwam13 have 

employed sensory and chemical means of influencing the arousal-levels of cats. They indicate a positive relationship between nystagmus 

output and increased levels of the animals' 

activity. 

In order to evaluate further the effect 

instructions on nystagmus production, a stu

was conducted using an analeptic to influen

the physiological arousal-level of subject

Normal clinical doses of amphetamine a

a placebo were administered subcutaneou

to groups of "rotation-naive" and "rotatio

experienced" subjects according to a count

balanced design. Subjects were used as th

own controls. Mental arithmetic and reve

instructions were utilized. Although signific

increases in cardiovascular activity occurred 

a result of drug administration, the influen

of the analeptic on nystagmus output was s

tistically negligible. However, the instructio

again produced highly significant effects. M

-5-
TABLE 3 

Mean total nystagmus output (degrees of slow-phase activity) and duration in seconds of the 

primary nystagmus for 6 "naive" and 6 "experienced" subjects exposed to a normal clinical 

dosage of amphetamine and to a placebo. Data were calculated from averages of two trials 

per subject under each condition. MA and REV refer to mental arithmetic and reverie instructions, respectively (stimulus: 4.1 ° I sec' for 13 seconds). 

ACCELERATION DECELERATION 

DRUG 

MA REV 

DEGREES 380 228 

SLOW-PHASE 

"Naive" 

Subjects SECONDS 49.8 43.8 

DURATION 

DEGREES 365 263 

SLOW-PHASE 

"Experienced" 

Subjects SECONDS 46.4 42.2 

DURATION 

tal arithmetic tasks resulted in significantly 

greater output of slow-phase nystagmus than 

did the reverie state. (See Table 3; Fig. 3.) 

These results indicate that the arousal variable 

in nystagmus output is less intimately related 

to the analeptic-produced changes in activity 

than to the kind of alertness influenced by instructions. They also point out the need for a 

caution in the evaluation of drug effects on 

nystagmus. Most such studies have employed 

tranquilizing or depressant-type drugs and 

have related resultant deterioration or absence 

of nystagmus to those areas of the brain on 

which the drug exerts a primary influence. In 

many cases, the main vestibular significance of 

the drug may be more general i.e., simply that 

the subject becomes relaxed and less mentally 

active. Studies of sedative compounds used in 

NO DRUG DRUG NO DRUG 

MA REV MA REV MA REV 

376 268 510 360 577 337 

47.5 42.2 58.7 50.0 57.6 43.0 

280 173 27.'5 249 309 155 

42.5 36.0 42.2 41.5 44.4 34.0 

conjunction with instructions influencing men

tal activity would be of interest. 

2. Low-magnitude, prolonged constant angu

lar acceleration. The effects of instructions o

the nystagmic response to accelerations of 1.8

and 1.0° /sec' were examined.• Aschan3 h

presented evidence indicating that the nysta

mic response terminates abruptly at the mome

of stimulus cessation when stimuli of 1.0° jse

are employed, and that a 50 per cent reductio

in response appears in the second followin

cessation when higher levels of stimulation a

used. Neither of these findings were verifie

when subjects were engaged in mental arith

metic (See Table 4). The data indicated tha

(a) Under the arithmetic condition cle

nystagmus appeared for all subjects through

out stimulation and never ended prior to, o

TABLE 4 

Average total slow-phase nystagmus and average duration of the response in seconds. Data 

are averages of two accelerations and two decelerations for each of 6 subjects. MA and ATS 

refer, respectively, to mental arithmetic and attending to the rotatory sensations (stimuli were 

1.0° / sec• for 84 seconds and 1.8° /sec• for 50 seconds). 

Stimulus Task 

"MA 

1.0° /sec• ATS 

MA 

1.8° /sec• ATS 

-6-

Degrees SlowPhase Nystagmus 

671.4 

298.1 

854.3 

159.9 

Nystagmus Duration 

in Seconds 

94.8 

57.2 

68.3 

27.3 
EXPERIENCED GROUP 

SUBJECT 2 - TRIAL 4 - REV - OECEL ZODEG 

:~ -+-- --v--' --1--,~ I 

DRUG ~ 

SUBJECT !i - TRIAL I - MA - ACCEL 

SUBJECT 6 - DRUG - ACCEL 

REV 

"NAIVE" GROUP 

SUBJECT 0 - TRIAL 3 - REV - ACCEL 

DOUG r===r: ~ 20 r· NO , 

DRUG ~ • ..J· ............... -.,....-..,-..--... --·--......... ------ --~-· • . I 

SUBJECT E - TRIAL 2 - MA - DECEL 

DRUG 

NO 

DRUG 

SU8JECT F - NO ORUG - OE<:a 

:::: I 

REV 

FIGURE 3. Nystagmus recordings obtained from rotation-experienced and rotation-naive 

subjects under conditions of mental arithmetic ( MA) and reverie (REV). Data were 

obtained under both conditions with a placebo and with a normal clinical dosage of amrhetamine. Stimulus periods ( 4.1° /sec• for 13 seconds) are denoted by the vertica bars 

through the records. Calibration markers at the right of each record indicate 20° eye 

excursions. 

at the moment of, stimulus termination. 

(b) When simply attending to the rather 

weak rotatory sensations elicited by these lowlevel accelerations, 58 per cent of the records 

showed either "zero" response or ended prior 

to, or at the moment of, stimulus termination. 

(c) A 50 per cent drop in slow-phase 

nystagmus velocity ( 1.8° /sec• stimulus) appeared 4-6 seconds after stimulus termination 

during arithmetic trials. 

In addition, two subjects who had demonstrated a high vestibular output in other experiments were tested under the mental arithmetic 

condition with a 0.5° /sec• stimulus applied for 

84 seconds in one case and llO seconds in the 

other. Results were similar to those obtained 

at 1.0° and 1.8 o / sec• (see Fig. 4). The data 

demonstrate that, when subjects are kept mentally alert, nystagmus does not cease abruptly 

with the termination of low-level accelerations 

( see Fig. 5 ) . 

Caloric Stimulation 

In order to determine whether the signifi

effects due to instructions could be general

to other methods of nystagmus elicitation

study of clinical procedures was conducted 

Table 1). Four variables were manipula

instructions ( MA and REV), fixation dista

( 30.5 em and 1.63 m) , subject experience, 

the presence or absence of vision.'0 Aver

data appear in Table 5 and the results may 

summarized as follows: 

1) The "naive" and "experienced" gro

did not differ significantly. 

2) In both light and darkness, nystag

was of greater amplitude and longer dura

while subjects were engaged in mental ar

metic than when they were instructed to re

3) Unlike responses to rotation, the cal

reaction was always present during rev

states. 

-7-
20 

>-

t0 

9 

w 15 

> 

C/) 

::> 

::E <J C) Q) 10 

~ C/) 

...... C/) tJ) 

>- Cll 

z 0 

w 5 

C/) 

~ 

:I: 

a. 

I 

~ 

0 

...1 0 

C/) 

MA ,.....--· ................ 

./·-·-/ \ 

/ . • STIMULUS \ I 1.8°/sec2 

• . \ 

·--· 

ATS o---o 

I _..o---o__ --<>-- ... -o---o •......_ o---o-- ""O- -o- .... ,...,o """"-• 

.;;~ ',, "' o -o---o- • 

10 20 30 40 50 

TIME IN SECONDS 

60 70 80 

FIGURE 4. Average slow-phase eye velocity (deg/sec) for 5-second intervals under conditions 

of merital arithmetic ( MA) and attending to the direction and intensity of the rotatory 

sensation ( ATS). Data arc averages for 6 subjects each given 2 accelerations and 2 decelerations under each condition. Arrow indicates point of stimulus termination ( 1.8° /sec' 

for 50 seconds) . 

TIME 

ISECI 

0-20 

21-42 

43-64 

65-86 

87-108 

109-124 

SUBJECT JMK- MENTAL ARITHMETIC- ACCELERATION 

STIMULUS-0 5~SEC2 FOR 110 SECONDS 

FIGURE 5. Nystagmus recording from a subject exposed to an acceleration of 0.5° /sec• for 

110 seconds while engaged in mental arithmetic. Vertical bars through the record indicate 

the stimulus period and an eye-excursion calibration appears at the end of the record. Note 

the beats occurring after stimulus termination. 

-8-
TABLE 5 

The average duration of caloric nystagmus, average slow-phase nystagmus output (total darkness), and average nystagmus rating in illumination (a 0-4 scale considering frequency, amplitude, and regularity of response) under conditions of mental arithmetic and reverie. Fixation 

distance in illumination was 30.5 em or 1.63 m (ceiling fixation). Data are averages for 16 

subjects tested with water at 30° C applied for 40 seconds. 

Total Darkness 

Task 

Average Nystagmus 

Duration (Sec.) 

Average Total Slow"Phase 

Nystagmus Output (Deg.) 

MA 

REV 

230.9 

194.5 

2310° 

1520° 

Task 

Illumination 

Average Nystagmus Examiner's Average 

Duration (Sec.) Rating ( 0-4 Scale) 

MA 

REV 

MA (cf) 0 

139.9 

124.8 

104.3 

2.1 

1.5 

1.3 

o indicates ceiling fixation (1.63 m) 

4) Ratings of the nystagmus response in 

illumination favored MA over REV trials. 

5) Near-fixation ( 30.5 em) yielded greater 

amplitude and duration of nystagmus than farfixation ( 1.63 m). 

6) Two of 8 subjects demonstrated no response during far-fixation. 

These data demonstrate that the nystagmic 

reaction to calorization is affected by instructions, although less markedly so than during 

rotatory stimulation (see Fig. 6). This is probably due to a combination of greater intensity 

of the caloric stimulus and increased apprehensiveness on the part of subjects in the caloric 

situation. Furthermore, the distance of the 

fixation point from the subject during aural 

irrigation in illumination is a critical variable. 

Not only is nystagmus reduced with far-fixation, 

but also, with 2 experimental subjects and 2 

others used in preliminary trials, no nystagmus 

was observed. 

General Discussion 

The series of studies outlined above has: 

( 1) confirmed and expanded notions regarding arousal-level and its effect on human 

vestibular nystagmus, ( 2) evaluated the efficacy of several techniques for providing some 

control of arousal-level, and ( 3) pointed to a 

possible explanation for conflicting or unusual 

results in theoretical or applied vestibular 

investigations. 

The early studies which noted changes 

nystagmus as some function of "excitement" 

physical tension pointed to the need for cont

over subjective states. Wendt""· 37 was proba

the first to establish some basis of reduc

the variability which results from subject

changes by his notion of an "environme

directed orientation." One of the means 

employed to maintain alertness was to ha

subjects imagine and attend to "a ship on 

horizon."23 Apparently some subjects could u

this technique and remain alert throughou

number of trials. 

It would appear, however, that the und

lying factor in subjective orientation may 

more accurately defined as some degree 

mental activity or, perhaps, as a psychologi

state of alertness or concerted attending. T

direction of a subject's orientation seems 

matter little, i.e., whether he is "inwa

directed" or not, so long as he is menta

active. Further, at least for a relatively sh

series of repeated vestibular stimulations, t

mental arithmetic task seems to provide t

least amount of trial-to-trial intra-subject va

ability and results in a vigorous, long-durati

nystagmus. Other recent studies have employ

arithmetic tasks to demonstrate changes 

caloric nystagmus. Mahoney, Harlan and Bic

ford.. and, later, Lidvall,27 used short ari

metic problems during nystagmus dysrhythm

to elicit a burst of regular nystagmus. Howev

-9-
·-·MA 

·-REV 

0 ~wm~~wrooo~~oo~oo~~~~~oo~oo~~~~~~~~~ 

TIME IN SECONDS 

FIGURE 6. Average slow-phase eye velocity for 4 subjects under conditions of mental arithmetic ( MA) and reverie (REV). Stimuli were 40 seconds of aural irrigation with water at 

30° C administered in illumination. "Zero" time indicates moment of stimulus termination 

and onset of total darkness. 

these investigators do not appear to have employed the task as a means of stabilizing 

subjective states throughout successive trials. 

Wendt"" has pointed out one of the main 

areas in which failure to control the alertness 

factor can result in possibly erroneous conclusions, i.e., habituation of nystagmus. Wendt 

claims that habituation in total darkness does 

not take place unless the subject is allowed to 

assume a "reverie attitude." Early studies, such 

as those by Dodge," Dorcus," and Griffith,'"· 17 

showed a markedly reduced response with 

repeated angular accelerations. Wendt, however, accredits these findings to a failure to 

control alertness. The same explanation probably accounts for at least some of the nystagmus 

decline recently reported for repeated caloric 

stimulations.'" 

Two other studies may be cited as examples 

where a lack of control of the arousal states of 

subjects probably produced results at variance 

with actual vestibular functioning. Thus, the 

report of Aschan" indicates no nystagmic response from some subjects and an immedia

cessation of nystagmus with stimulus termina

tion from others, when acceleration values o

1.0° jsec• are employed. He relates this to th

notion that, at such a low level of acceleration

only a torsion of the cupula occurs, since th

stimulus is too weak to cause the end-orga

to slide along the crista. His findings, howeve

are not confirmed when subjects are kep

mentally active. Further, the rapid decline o

nystagmus after stimulus cessation reported fo

higher-level accelerations also does not appea

when appropriate subject-tasks are assigned

Only during conditions of reduced mental activ

ity have subjects used in the present repor

demonstrated examples of As chan's findings. 

The second investigation, by Suzuki an

Totsuka,"' made note of inconsistent nystagmu

responses from some subjects during a serie

of repeated accelerations and, from others, "

temporary reduction in response followed by 

complete and lasting restoration of nystagmus

It is almost certain that the reported fluctua

-10-
tions were due to changes in the subjects' states 

of alertness. 

For any given series of repeated stimulation 

of the vestibular system, some task-control of 

the subject's mental activity level appears 

necessary. Further, two other factors must be 

considered: (a) if subjects are permitted to 

close their eyes, arousal is probably affected .. 

and, it has been demonstrated that, even if 

subjects are in total darkness, eye-closure results in a reduced nystagmus response when 

the cameo-retinal-potential method of recording is employed;.. (b) with prolonged or 

repeated exposure to a given set of conditions, 

the various stimuli involved probably lose their 

arousal value. This has been demonstrated for 

auditory stimuli." 

Thus, it is suggested that, for short series 

of stimulations, arithmetic tasks be assigned 

to subjects to provide some control over their 

mental activity. For long stimulus series, a 

variety of tasks is probably necessary to maintain arousal level. The use of simple tasks 

which require sustained mental activity should 

reduce variability of the nystagmic response 

not due directly to vestibular function and permit a more adequate evaluation of vestibular 

processes, per se. This approach does not 

contradict the possibility that the normal course 

of events may be for both the subjective and 

nystagmic aspects of vestibular function to rise 

and decline at comparable rates in the absence 

of extraneous stimuli. • 

Some notion of the subject's mental activity 

appears to be a prerequisite for proper evaluation of vestibular responses in practical situations, e.g. in clinical diagnosis, maneuvers 

of air or space vehicles, etc. With respect to 

the latter, it is of interest that, although evidence is conflicting, several studies •· •· 

31 have 

indicated that gross qualitative and quantitative 

changes in nystagmus may occur as a function 

of alertness without a significant change in 

EEG pattern. That is, in the evaluation of 

the effects of certain maneuvers or environmental conditions, the absence of nystagmus 

in a subject may be a signal of reduced mental 

activity which it too subtle to be detected by 

EEG tracings, rather than a lack of vestibular 

stimulation. If the nystagmograms show the 

wandering, autogenous eye movements m

tioned by Wendt, 36 this is almost certainly 

case.• 

A point of more general application sh

also be made. The data reviewed in the pre

report indicate the importance of the subj

state of arousal on the reactions elicited thro

stimulation of what has been frequently 

garded as a "reflexive system." It is poss

that much "reflex activity" is significa

influenced by the subject's state of alertn

Further, this "psychological tonus" may h

implications for the evaluation of clinical ca

SUMMARY 

Investigations concerned with the effect

subjective states on vestibular nystagmus w

reviewed. Methods of controlling such st

were discussed. Data indicate that the sig

cant factor in subject-orientation is a stat

arousal, defined in terms of mental activ

Continuous, concerted attending to a task yi

a brisk, long-duration nystagmus. If respo

to a task require less attention with rep

tion, or if subjects are not kept alert

significant reduction in nystagn}us output 

occur. A sudden alerting stimulus may t

occasion a burst of nystagmic activity in 

apparently "adapted" individual. Knowle

of subjectives states is a pre-requisite for pro

evaluation of vestibular responses in theoret

formulations, in many clinical situations, 

in ascertaining vestibular components ass

ated with air- or space vehicle maneuvers. 

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