AM-65-18 

ADAPTATION TO VESTIBULAR DISORIENTATION: I. 

Approved by 

VERTIGO AND NYSTAGMUS FOLLOWING 

REPEATED CLINICAL STIMULATION 

William E. Collins, Ph.D. 

Released by 

~ ~~ {\ '-'rr\o-h~..r- STANLEY R. MoHLER, M.D. 

g; 4 ird M. s. WHITE, M.D. 

DIRECTOR, CARl 

May 1965 

FEDERAL AVIATION AGENCY 

Office of Aviation Medicine 

Civil Aeromedical Research Institute 

Oklahoma City, Oklahoma 

FEDERAL AIR SURGEON 
Adaptation to Vestibular Disorientation: I. 

Vertigo and Nystagmus Following Repeated Clinical 

Stimulation 

Recent studies have been concerned with the 

effects of repeated unilateral caloric irrigations 

on human nystagmus and vertigo. Lidvan•-• recorded nystagmus from behind closed eyes and 

reported habituation (a response decline) with 

as few as 4 repeated stimulations. Number of 

nystagmic beats and duration of the response 

both declined, while latency of response and 

degree of dysrhythmia increased. In addition, 

subjective responses (vertigo) declined markedly. Fluur and Mendel 4

'

5 used the duration 

of nystagmus recorded with the subjects• eyes 

closed as their primary measure and obtained 

a shortening of nystagmus time after 8-12 unilateral irrigations. The latter authors also examined ·before-and-after responses to stimulation of each ear with warm and with cool water 

and reported that subjects fell into two groups: 

( 1) those who exhibited a directional preponderance in the unhabituated direction, and ( 2) 

those who showed reduced responses in both 

directions! A later study indicated that the 

directional preponderance following a habituation series could be reversed by then habituating the opposite direction. 5 

Forssman, Henriksson, and Dolowitz" kept 

subjects in total darkness, and Forssman7 later 

used an illuminated environment to investigate 

the effects of repeated unilateral calorizations 

on nystagmus, laterotorsion, and vertigo. Results for the two studies were similar. Twelve 

stimulations produced declines in vertigo in 

excess of 80%, laterotorsion declined about 40%, 

and the maximum eye-velocity and the duration of nystagmus were reduced by 55% and 

25%, respectively. 

The importance of alertness or arousal on the 

process of habituation was noted in several of 

the above studies e.g. "·" and has received extensive attention elsewhere. •-u It has been 

demonstrated that nystagmic output• and evidence of dysrhythmia in records of nystagmus 

can be readily manipulated by instructions 

given to the subjects. Subjective states of 

arousal result in brisk nystagmic responses. 

Thus, in this study, efforts were made to control for the arousal factor. 

The present study was designed to examine 

the effects on nystagmus and subjective experience of repeated unilateral caloric irrigations administered under conditions of total 

darkness and of visual fixation. Tasks were assigned to subjects in an attempt to control mental states. Pre- and posttests comprised stimuli 

which elicited unilateral and bilateral nystagmic responses in both directions. 

METHOD 

Subjects. Subjects were 20 males between 

the ages of 21-29. All were experimentally 

naive and were free of any history of ear difficulties, dizziness, loss of consciousness, or unusual reactions to linear and angular accelerations. On each day, prior to testing, subjects• 

ears were examined and cleaned. 

Apparatus. Two water baths were equipped 

with Bronwill constant temperature circulators. 

Tubing from each bath terminated in its own 

plastic nozzle which was to be inserted in the 

external auditory meatus. Water temperature 

was maintained such that it was 30° C from 

one bath, and 44 o C from the other, upon introduction to the ear. 

Horizontal components of eye - movements 

were obtained by means of an Offner Type 

TC recorder. A 3-sec RC time constant was 

-1-
employed in amplification. Signals were picked 

up from electrodes taped near the outer canthi. 

An indifferent electrode was located on the 

forehead. All recordings of nystagmus were 

obtained in total darkness with the subjects' 

eyes open. Subjective reactions were signalled 

by means of a buzzer manually controlled by 

the subject. 

the back of the basin. A tube extended from 

the drain into a large water receptacle placed 

underneath the examining table. A large number of irrigations could thus be performed without any discomfort to the subjects and without 

concern for collecting the water. 

A special device (Caloric Irrigation Receptacle) to collect return flow of water from the 

ear in a convenient fashion was a rectangular 

plastic basin into which the subject's head was 

placed and anteverted approximately 30° by 

means of a head rest. A drain was located at 

Procedure. Subjects were divided into two 

groups of 10 each. Both groups were tested on 

7 occasions. Six of these occasions were on 

consecutive days; the seventh was one month 

later. The first, sixth, and seventh days were 

termed pretest, post-1 and post-2 tests respectively, and each comprised 6 trials, the order 

of which was varied as indicated in Table I. 

Groups 

lli!:k 

Fixation 

23 

Q) ~ 

P::E-o! 

g 

:jj 

~23 

.a ~ ..... Eo-! 

~ 

0::: 

'"tj23 

; ~ E-4 

'7C'I 

1;;~ 

~~ 

TABLE I 

TilE ORDER OF STIMULUS PRESENTATION. RAND L REFER 

TO THE RIGHT AND THE LEFf EAR; c AND w INDICATE COOL 

(30°C) AND WARM (44°C) STIMULI. BILATERAL STIMULI WERE 

ADMINISTERED FOR 15 SEC, UNILATERAL STIMULI FOR 30 SEC. 

ALL PRE AND POST TESTS WERE CONDUCTED IN TOTAL 

DARKNESS. 

SUBJECTS 

RY PH RA BE GR JB HL JL BM 

TV FN GP FS cw DM FG FK RV 

R.L .. R .. L, R.L .. R .. L. R.L .. R .. L. R.Lw R .. L. R.L .. 

R .. L. R.L .. R .. L. R.Lw R .. L. R.L .. R .. L, R.L .. R .. L. 

L. L. R. L. R. L .. R .. L ... R .. 

R .. R. L. L.. R .. R .. L .. R. R. 

L .. L.. R .. P..., L. L. R. L. L. 

R. R .. L .. R .. L.. R. L. R .. L.. 

Dark group: 10 unilateral trials (all R.) per day for 4 days. All trials in 

total darkness. 

Fixation group: 10 unilateral trials (all It) per day for 4 days. Trials 1 

and 10 on each day in total darkness. All other trials in 

illumination with visual fixation. 

L. L. R. L. L. L.. R .. L.. R ... 

R .. R. L. L .. R .. R .. L .. R. R. 

L.. L .. R .. R. L. L. R. L. L. 

R. R .. Lw R .. L .. R. L, R .. L.. 

R.L.. R .. L, R.L .. R .. L, R.L.. R .. L. R.L .. R .. L, R.L .. 

R .. L. R.L .. R .. L, R.Lw RwL. R.L .. R .. L. R.L .. R .. L. 

-2-

JG 

vv 

R.L, 

R.L ... 

L .. 

L, 

R ... 

R. 

Lw 

L. 

R .. 

R. 

R ... L, 

R.L.. 
Two of the 6 trials were bilateral irrigations 

( warm water to one ear and cool water to the 

other delivered simultaneously). The remaining 4 trials consisted of unilateral irrigations (a 

warm or a cool stimulus applied to each ear 

separately). Days 2 through 4 consisted of 

10 daily habituation trials. In all 40 of the 

latter, a unilateral stimulus of 30° C was applied to the right ear. Twenty to 30 minutes of 

rest occurred between successive stimulations. 

The two groups of subjects were differentiated on the basis of the habituation trials. The 

Dark Group received all trials in total darkness. 

The Visual Fixation Group was given all preand posttests in total darkness, but in the habituation series only trials 1 and 10 on each 

day were in darkness. The remaining daily 

trials for the Visual Fixation Group were in 

illumination with the subjects actively fixating 

on the center marker of the calibration device 

on the ceiling and consciously trying thereby 

to reduce and prevent the nystagmic movement. Thus, the Dark Group received a total 

of 40 habituation trials in total darkness while 

the Visual Fixation Group received 8 habituation trials in total darkness and 32 under conditions of visual fixation. 

During all "total darkness" trials, the irrigation period was also in the dark. The rate of 

flow of the water was relatively high, approximately 15ccjsec, to permit ready monitoring of 

the irrigation by touch alone. Irrigation time 

was 15 sec for bilateral and 30 sec for unilateral 

stimuli. 

Tests were conducted in the following manner: Subjects assumed a supine position on the 

examining table with their heads elevated and 

anteverted approximately 30°. Prior to each 

trial, eye-movement calibrations were obtained 

by means of a ceiling panel with a center and 

two lateral markers. For all pre- and posttests, 

subjects signalled the onset, point of maximum 

intensity (defined as the point at which the 

sensation no longer increased), and cessation of 

their subjective vestibular experiences by means 

of a manually operated microswitch. Several 

seconds after their "cessation of sensation" signal, subjects were given mental arithmetic 

( MA) problems (continuous division) to perform throughout the remainder of the trial. 

The MA task was used purely as an alerting 

technique. •-n At the conclusion of each preand post-trial, subjects described their sensations and rated them. 

Subjective ratings were made in the following fashion. During the pretest, the first two 

trials for all subjects were bilateral irrigations. 

Each subject was asked which of the two bilateral stimulations produced the most intense 

subjective experience. His selection was then 

given a rating of 100 and all other subjective 

ratings were made with the "100 intensity" experience as a reference point. 

During the habituation trials in total darkness, several tasks were presented to the subjects in accordance with the schedule in Table II. 

All used the microswitch as a signalling device. The tasks included: 

1) Reaction time ( RT) - Subjects responded to a series of 500 cps tones of 1/10 sec 

duration by depressing the microswitch as 

quickly as possible at the onset of each tone. 

2) Temporal Estimation of Sound - Filled 

Intervals ( FI ) - The 500 cps tone was sounded 

for periods ranging between 0.5 and 6.5 sec. 

At the conclusion of a tone, subjects attempted 

to reproduce its duration by depressing the 

microswitch for the same length of time as 

that occupied by the tone. 

3) Temporal Estimation of Sound-Bounded 

Intervals (BI) - The 500 cps tone was sounded 

for 1/10 sec to indicate the start and end of 

an intervening period of silence. Silent periods 

between the two brief tones ranged from 0.5-

6.5 sec. After each pair of tones, subjects depressed the microswitch for a length of time 

which they considered to be equal to that of 

the period of silence between tones. 

4) Temporal Comparison of Sound-Filled 

Intervals ( FIC) - Pairs of 500 cps tones were 

successively presented for comparison. A given 

tone would be of a duration ranging from 0.5-

6.5 sec. Its companion tone would differ by 

no more than 2 sec. Subjects indicated which 

tone of the pair was longer in duration by signaling with either one or two depressions of 

the microswitch. 

5) Temporal Comparison of Sound-Bounded 

Intervals ( BIC) - A period of silence was 

-3-
TABLE II 

THE ORDER OF TASK PRESENTATION FOR THE DARK 

GROUP AND FOR THE VISUAL FIXATION GROUP. RT = REACTION TIME; FI AND BI =TEMPORAL ESTIMATION OF SOUNDFILLED AND OF S 0 UN D - B 0 UN DE D INTERVALS, RESPECTIVELY; FIC AND BIC =TEMPORAL COMPARISON OF SOUNDFILLED INTERVALS AND OF SOUND-BOUNDED INTERVALS, 

RESPECTIVELY. 

Habituation Sessions 

Trials 

1 

2 

3 

4 

5 

6 

7 

8 

9 

10 

I 

FI 

FI 

FI 

RT 

BI 

BI 

BI 

RT 

FI 

BI 

II III 

Dark Group 

FIC BI 

FIC BI 

FIC BIC 

RT BIC 

BIC RT 

BIC FIC 

BIC FIC 

RT RT 

FIC FI 

BIC FI 

IV 

BIC 

BIC 

BI 

BI 

RT 

FI 

FI 

RT 

FIC 

FIC 

Trials Visual Fixation Group 

1 FI FIC BI BIC 

2 

Through 

9 

Illumination with Visual Fixation 

10 BI 

delimited by two 1/10 sec, 500 cps tones and 

was followed by another pair of tones with an 

intervening period of silence. Silent periods 

ranged from 0.5 - 6.5 sec, but in each pair of 

silent periods the maximum temporal difference did not exceed 2 sec. Subjects depressed 

the microswitch once or twice to indicate 

whether the first or second silent period was 

longer in duration. 

BIC FI FIC 

For each of the above tasks, a whole series 

of stimuli were presented throughout a trial. 

The tasks were used purely to maintain a state 

of alertness in the subjects. However, subjects 

were encouraged to perform as accurately and 

as attentively as possible and were impressed 

with the fact that their performance was of 

significance. Records of their signals were 

obtained. 

-4-
RESULTS AND DISCUSSION 

Nystagmus 

Eye-movement recordings (see Figures 1 and 

2) were scored and analyzed for duration of 

nystagmus, slow-phase displacement, and number of nystagmic beats as indicated elsewhere." 

Mean data for both the Dark Group and the 

Visual Fixation Group appear in Table III. 

Percentage data relating the posttest scores to 

those of the pretest appear in Table IV. In 

both tables, scores have been rounded off to 

the nearest whole number. 

The data were treated statistically by analyses of variance and t tests (Tables V and VI). 

In all analyses, as expected, significant differences were obtained among subjects. In addition, "Ears" yielded significant differences for 

all measures due to the fact that higher scores 

were consistently obtained for bilateral, as compared with unilateral, irrigations. 

TABLE III 

MEAN DURATION, NUMBER OF NYSTAGMIC EYE MOVEMENTS, AND SLOW-PHASE DISPLACEMENT OF THE EYES TO 

PRELIMINARY, POST-1, AND POST-2 TESTS FOR THE TWO 

GROUPS. EACH VALUE IS A MEAN FOR 10 SUBJECTS. 

Dark Group Fixation Group 

Pre Post-1 Post-2 Pre Post-1 Post-2 

Duration ( Seconds~ 

R.Lw 172 182 173 191 191 172 

RwLc 168 153 163 193 186 170 

R. 154 152 158 174 169 155 

Lw 136 156 147 174 180 163 

Rw 123 130 124 172 156 155 

L. 135 139 136 180 179 154 

Number of Beats 

R.Lw 250 326 285 287 316 291 

RwL. 215 248 255 272 318 294 

R. 193 231 242 233 242 215 

Lw 174 242 223 227 245 218 

Rw 136 200 192 223 234 220 

L. 158 177 176 246 249 228 

Slow-Phase Displacement (Degrees) 

R.Lw 1991 2124 1926 2997 2403 2557 

RwL. 2016 1644 1847 3000 2629 2374 

R. 1389 1271 1433 2166 1537 1430 

Lw 1331 1403 1236 1907 1512 1488 

Rw 961 1203 1128 1976 1793 1521 

L. 1196 1150 1071 2174 1920 1525 

-5-
BILATERAL (R-3Q•C; L-44°C) FOR 15 SEC 

PRE 

POST-I .rv 

UMLATERAL (R-30-c) FOR 30 SEC 

PRE 

POST- I 

UNILATERAL (L-30•C) FOR 30 SEC 

PRE 

POST-I J~ 

SUBJECT FS 

.oL I SEC 

40L I SEC 

40"L_ I SEC 

40L I SEC 

40"l_ I SEC 

..oL_ I SEC 

FIGURE 1. Examples of nystagmus recorded from a subject in the Visual Fixation Group. Vertical bars through the 

records indicate the point at which the irrigation was terminated. Calibration markers appear at the end 

of each tracing. A clear decline in slow-phase displacement is evident in post-1 tests for the practiced 

direction (bilateral trial and unilateral R-30° C trial). 

-6-
BILATERAL (R-44•C; L-3QOC) FOR 15 SEC 

PRE 

POST-I 

UNILATERAL (R-44•C) FOR 30 SEC 

PRE 

UNILATERAL {L-44°C) FOR 30 SEC 

PRE 

POST-I 

SUBJECT GR 

FIGURE 2. Examples ,of nystagmus recorded from a subject in the Dark Group. Markings are the same as in Figure '1. 

In pretests, this subject showed remarkably low nystagmic output. The increased number of nystagmic 

movements in post-1 is especially clear for the practiced direction (unilateral L-44 o C). 

-7-
For the Dark Group, the habituation series 

produced no statistically significant changes in 

duration or in slow-phase activity. The number of beats of nystagmus, however, rose significantly from pre- to post-1 and showed no 

evidence of normalizing after one month with 

no stimulation ( post-2). 

The Visual Fixation Group was affected differently. Whereas there was no change in the 

number of beats of nystagmus from the pre- to 

the posttests, slow-phase displacement declined 

significantly from pre- to post-1 and, after one 

month of rest, the response showed some further decline. The duration of nystagmus for 

the fixation group showed no pre- to post-1 

change, but a statistically significant decline 

occurred in post-2. 

Dysrythmia occurred on a number of occasions during the habituation trials. However, 

any alerting stimulus would restore a brisk 

nystagmus. Moreover, based upon observations made both prior to and during the exTABLE IV 

RELATION OF DATA FROM POST-I AND POST-2 TESTS TO 

PRELIMINARY TEST SCORES. ALL VALUES ARE PERCENTAGES 

CALCULATED FROM DATA IN TABLE 3. 

Dark Group Fixation Group 

Post-1/Pre Post-2/Pre Post-1/Pre Post-2/Pre 

Duration 

aLw 106 101 100 90 

RwLc 91 97 96 88 

a 99 103 97 89 

Lw 115 108 103 94 

Rw 106 101 91 90 

L. 103 101 99 86 

Number of Beats 

aLw 130 114 110 101 

RwLc 115 119 117 108 

a 120 125 104 93 

Lw 139 128 108 96 

Rw 147 141 105 99 

L. 112 111 101 93 

Slow-Phase Displacement 

aLw 107 97 80 85 

RwL. 82 92 88 79 

a 92 103 71 66 

Lw 105 93 79 78 

Rw 125 117 91 77 

L. 96 90 88 70 

-8-
TABLE V 

SUMMARY OF ANALYSES OF VARIANCE (REPEATED MEASUREMENTS DESIGN). 

F-Ratios 

Total Darkness Group Visual Fixation Group 

Nystagmus Number Slow-Phase Nystagmus Number Slow-Phase 

Source df Duration of Beats Nystagmus Subjective Duration of Beats Nystagmus Subjective - Subjects ( S ) 9 3.42" 10.79" 7.78b 3.89b 5.46b 3.24" 7.84. 3.17" 

Tests(T) 2 0.38 6.56b 0.18 1.92 3.63" 1.65 6.60b 5.59" 

Directions (D) 1 5.59" 10.34" 3.21 3.76 0.11 0.01 0.84 14.77• 

Ears (E) 2 37.97• 76.07• 6.99" 29.04. 12.96. 83.41. 73.20. 63.66. 

SXT 18 1.76" 3.23b 1.96 2.82b 3.92' 3.0~ 2.51" 2.79b 

s xn 9 6.3o· 4.56b 4.83b 1.95 3.24" 4.29b 2.68" 0.68 

SXE 18 1.06 1.42 1.75 1.85 0.82 0.74 2.06 0.92 

"' I TXD 2 1.11 2.82 0.29 7.86b 0.61 0.15 2.11 3.45 

TXE 4 6.62. 2.92" 0.90 6.2o· 0.74 0.83 0.17 0.88 

DXE 2 4.02" 1.82 0.29 13.48. 0.08 0.63 1.26 3.13 

SXTXD 18 1.72 1.94" 2.87b 1.33 0.83 1.67 5.59. 0.91 

SXTXE 36 0.99 0.71 2.70b 1.97" 1.44 2.42b 8.06" 1.20 

sxnxE 18 0.82 1.93" 2.33" 2.08" 2.16" 2.26" 4.78. 2.17" 

TXDXE 4 1.15 1.25 5.66· 1.94 0.36 0.59 2.64 3.62" 

SXTXDXE 36 

-- --· 179 

Levels of Significance 

a: .05 level 

b: .01 level 

c: .001 level 
Measure 

Frequency 

(fast-phase 

to the right) 

°Frequency 

(fast-phase 

to the left) 

Subjective 

(motion to 

the right) 

•subjective 

(motion to 

the left) 

Duration 

Slow-Phase 

Subjective 

(motion to 

the right) 

0 Subjective 

(motion to 

the left) 

TABLE VI 

RESULTS OF t TESTS 

Dark Group 

Comparison t 

Pre vs. Post-1 3.67 

Pre vs. Post-2 2.64 

Post-1 vs. Post-2 0.027 

Pre vs. Post-1 2.92 

Pre vs. Post-2 2.86 

Post-1 vs. Post-2 0.37 

Pre vs. Post-1 0.34 

Pre vs. Post-2 0.14 

Post-1 vs. Post-2 0.41 

Pre vs. Post-1 3.80 

Pre vs. Post-2 3.39 

Post-1 vs. Post-2 2.14 

Visual Fixation Group 

Pre vs. Post-1 0.53 

Pre vs. Post-2 1.99 

Post-1 vs. Post-2 2.91 

Pre vs. Post-1 3.58 

Pre vs. Post-2 2.77 

Post-1 vs. Post-2 0.49 

Pre vs. Post-1 0.75 

Pre vs. Post-2 0.13 

Post-1 vs. Post-2 1.25 

Pre vs. Post-1 6.64 

Pre vs. Post-2 3.01 

Post-1 vs. Post-2 4.53 

Level of Significance 

.01 

.05 

.05 

.05 

.01 

.01 

.05 

.01 

.05 

.01 

.05 

.01 

0

Direction stimulated during the 40 habituation trials. 

-10-
periment, it appeared that some of this 

dysrhythmia may have been related to the gazelevel of the subjects' eyes. That is, with repeated testing in the dark, there is a tendency 

not only for alertness to decline, but for some 

individuals to lower their gaze (and probably 

half-close their eyelids). At least for some 

subjects, this appears to produce dysrhythmia. 

With an "eyes closed" condition, it is suggested 

that subjects may inadvertently roll up their 

eyes and occasion a like effect. 

Dysrhythmia rarely occurred on the RT 

trials, perhaps because they were used sparingly (although subjects seemed to respond to 

them in a particularly attentive fashion), and 

on only one occasion during the pre- and posttests. It is probable that any task repetitively 

administered, especially in total darkness, will 

lose its ability to hold a subject's interest. Responses to timing tasks have been known to 

become quite automatic and such tasks, though 

providing relative ease of presentation and the 

possibility of variation, may not be particularly 

well suited for prolonged maintenance of 

alertness. 

Subjective Responses 

The mean intensity ratings reported by the 

subjects appear in Table VII. In addition, for 

both groups, the percentage the posttest ratings 

were of the pretest are included. For the Dark 

Group, a statistically significant decline in subjective vestibular experiences was obtained for 

the direction of response stimulated during the 

habituation trials. There were no significant 

pre- to posttest differences for the group of 

"unpracticed" direction stimuli, although two 

sets of these responses (to Rw and to Lc) showed 

higher intensity ratings. 

The Visual Fixation Group reported subjective declines for all post-1 stimuli. Further, a 

directional consistency was evident. The 

greatest drop occurred to the habituation stimulus ( R), next to the RcLw, and next to the 

Lw stimuli. The forementioned all produced responses in the same direction as that elicited 

during the habituation trials and the declines 

were statistically significant. Although the remaining three stimuli also showed reductions in 

intensity ratings, the pre- to posttest differences were not significant. 

Mter one month with no intervening tests, 

recovery of subjective intensity was evident for 

both groups. Some directional effects were 

still in evidence. 

The signals made by the subjects to indicate 

the start, peak, and end of their sensations were 

also examined. Measurements were made from 

the end of the irrigation to each signal, converted to seconds of time, and separately averaged for the Dark Group and the Visual Fixation Group (Table VIII). For stimuli eliciting 

responses in the same direction as the habituation trials (i.e., RcLw, Rc, and Lw), the preto posttest changes were approximately the 

same for the two groups. In general, latency 

increased, maximum intensity was reached earlier, and duration declined. 

For stimulation in the direction opposite that 

of the habituation trials (i.e., RwLc,Rw, and Lc), 

duration of sensation remained approximately 

constant for both groups from the pre- to posttests. However, for the Visual Fixation Group, 

latency increased and maximum intensity was 

reached at about the same point in time while, 

for the Dark Group, latency declined slightly 

and the peak intensity occurred earlier. The 

term "peak" may be misleading. Sensations 

were relatively rarely reported as building up 

to a point and then declining. Most often the 

sensation was reported as reaching an intensity maximum which was maintained for a considerable period of time before the sensation 

faded away. 

There were considerable differences among 

the sensations reported by the subjects. Apparent angular motion about an earth-vertical 

axis (including complete revolutions) was a 

frequent report following bilateral irrigations. 

The location of the turning axis was either in 

the stomach-chest area of the body or in the 

head - never at the lower extremity. The apparent velocity experienced during these turns 

varied widely and, on two occasions, subjects 

positively identified motion in the same direction for both the RLw and the RwLc stimuli. 

"Arcing" sensations were frequently reported in 

which subjects experienced repeated motion 

through one small angle (say, 45°), usually 

-11-
TABLE VII 

MEAN SCORES FOR THE INTENSITY OF THE SUBJECTIVE 

EXPERIENCE RESULTING FROM CALORIC IRRIGATION. WHICHEVER OF THE TWO BILATERAL IRRIGATIONS IN THE PRELIMINARY TEST PRODUCED THE STRONGEST SENSATION WAS 

GIVEN A RATING OF 100. ALL OTHER RATINGS WERE MADE 

BY COMPARING A NEW SENSATION WITH THE STANDARD OF 

100. 

Dark Group Fixation Group 

Mean Subjective Rating 

Pre Post-1 Post-2 Pre Post-1 Post-2 

RLw 87 41 50 95 47 54 

RwL. 84 59 113 73 66 75 

R 36 19 27 31 8 19 

Lw 56 39 47 45 29 49 

Rw 39 66 53 44 37 46 

L. 30 35 29 48 41 46 

% Post-1 and Post-2 Are of Pre Rating 

Post-1 Post-2 

R.Lw 47 57 

RwL. 70 135 

R 53 75 

Lw 70 84 

Rw 169 136 

L. 117 97 

without ever experiencing the return movement to the starting position; movement thus 

appeared always to start from the same point, 

was repeated through the same angle, but was 

experienced in only one direction. Other reports included dizziness, "arcing" about a horizontal axis, floating straight up, tilting to one 

or the other side, and elevation or depression 

of the feet. Many reports indicated combinations of displacement sensations. On a few occasions subjects noted secondary reactions (e.g., 

a subject would report an initial sensation of 

apparent angular motion to the left which, 

after a time, would give way to apparent motion to the right). The differences in reports 

Post-1 Post-2 

50 57 

90 103 

26 61 

64 109 

84 105 

85 96 

did not seem to be related to head position; 

the same subject in apparently the same position might report a clear turning sensation to 

one stimulus and, to the next, a clear tilt sensation accompanying the turn. 

No sensation was reported for 5 post-1 trials 

in the Visual Fixation Group ( 3 R. and 2 Lw) 

and for 4 post-1 trials in the Dark Group (2 R.,, 

1 Lw, and 1 L.). During post-2, 3 R. trials resulted in no reported sensation ( 1 in the Dark 

Group and 2 in the Visual Fixation Group). 

Of the total of 360 pre- and posttest trials, 

on only 3 occasions did the subjective experience begin before the onset of nystagmus. 

Whereas nystagmus was usually in evidence 

-12-
TABLE VIII 

MEAN TIME IN SECONDS FOR ONSET, POINT OF MAXIMUM 

INTENSITY, AND END OF SUBJECTIVE EXPERIENCE FOR THE 

TWO GROUPS. TIME WAS CALCULATED FROM THE END OF 

IRRIGATION TO THE SUBJECTS' SIGNALS. MOTION TO THE 

LEFT RESULTED FROM RLw, R, AND Lw STIMULI, TO THE RIGHT 

FROM RwL., Rw, AND L. STIMULI. 

Dark Group Visual Fixation Group 

Direction 

of Motion Test Onset Maximum End Onset Maximum End 

Left 

Right 

Pre 

Post-1 

Post-2 

Pre 

Post-1 

Post-2 

9.1 

18.4 

9.9 

9.9 

9.0 

8.5 

42.7 

40.8 

33.7 

43.5 

34.6 

32.7 

prior to the end of irrigation (in 226 of 240 

unilateral trials and 82 of 120 bilaterial trials), 

·the subjective response rarely began until the 

irrigation was terminated (in only 22 of the 

unilateral trials and 5 of the bilateral trials did 

it occur during the irrigation period). On the 

average, nystagmus preceded the subjective response by 10.4 - 21.3 sec for bilateral stimuli 

and by 17.8 - 32.0 sec for unilateral stimuli 

(see Table IX). 

81.1 

65.5 

63.2 

71.9 

68.9 

69.1 

9.1 

15.8 

15.5 

8.0 

15.5 

12.5 

42.5 

36.4 

37.4 

41.3 

39.2 

39.2 

80.1 

67.5 

73.6 

80.4 

85.3 

79.6 

General Discussion 

These findings indicate that, when alertness 

is maintained, remarkable declines in nystagmic 

output and duration do not necessarily occur 

during the course of repeated testing. In fact, 

an overall increase in number of nystagmic 

beats may appear as a result of successive trials 

in total darkness (see also Collins, 1964). It 

is, then, not always appropriate to consider 

TABLE IX 

MEAN TIME IN SECONDS BETWEEN START OF NYSTAGMUS 

AND ONSET OF SUBJECTIVE EXPERIENCE. SUBJECTIVE SIGNALS PRECEDED NYSTAGMUS ON ONLY THREE OCCASIONS. 

Dark Group Visual Fixation Grou:e 

Trials Pre Post-1 Post-2 Pre Post-1 Post-2 

Bilateral 12.8 21.3 18.3 10.4 19.3 12.9 

Unilateral 20.7 32.0 26.5 2·2.4 24.7 17.8 

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habituation (a response decline) as the only 

effect of repeated stimulation. The form of 

the response may change. 

The studies cited earlier which used a relatively small number of irrigating stimuli and 

yet found high rates of nystagmus loss in total 

darkness (whereas here there were no losses 

and, in the case of number of beats, a significant response increase) differed in two major 

respects from the present work: ( 1) state of 

arousal was not controlled; ( 2) data were 

obtained in darkness with the subject's eyes 

closed. These two conditions probably interact 

to lower nystagmic output. 

Contrary to data reported by Forssman and 

his associates, "'7 the effects of darkness and 

light on the nystagmic response appear different. Neither duration nor frequency showed 

any pre- to post-1 decline for the Visual Fixation Group, whereas the slow-phase output 

dropped significantly. The importance of the 

light condition is probably not the mere presence of visual objects. It seems most likely 

that what is required is an active attempt on 

the part of the subject to control and suppress 

his eye movements. 

In agreement with the previously cited study 

of the effects on nystagmus of repeated angular 

accelerations, 11 

a one-month rest period did 

not restore the alterations in the response produced by the repeated stimulation. Thus, for 

the Dark Group, number of nystagmic movements remained at a higher level than in the 

preliminary tests and, for the Visual Fixation 

Group, further declines in slow-phase output 

and in nystagmus duration were evident, rather 

than a return toward the preliminary response 

level. 

Although some directionally specific effects 

are suggested by the nystagmus data, they are 

neither consistent nor striking. This too agrees 

with the rotation findings noted above. 

Subjective responses showed statistically 

significant declines only for the practiced direction and insignificant changes for the unpracticed direction for both the total darkness and 

the visual fixation conditions. However, there 

was considerably less uniformity in the pre- to 

posttest changes for the total darkness condition 

and the marked increase in subjective intensity 

reported for Rw during the posttests (see Table 

VII) was accompanied by an enhanced 

nystagmic output (see Table IV). Unlike the 

nystagmic response, recovery of subjective 

intensity is clearly evident following the onemonth rest period. These results also agree 

with our previous rotatory work u 

Thus our data indicate that repeated, caloric 

stimulation results in a modified nystagmic 

response (which may reflect increased activity 

rather than a reduction) and that the modification is not capricious; the response shows little 

or no recovery toward its original form after 

a month of rest. The changes are bidirectional 

(although the repeated stimulation was unidirectional) and the nature of the changes 

seems to depend upon whether the response 

was repetitively elicited in darkness or with 

fixation. The subjective response declines for 

the practiced direction. Subjective reactions to 

the unpracticed direction, taken as a whole, 

show no statistically significant change although 

some declines or increases in intensity may be 

related to whether the total darkness or the 

visual fixation condition was present during 

stimulus repetition. Differential effects of 

visual fixation and total darkness during 

repeated testing have been reported for both 

nystagmic and subjective responses under other 

conditions of stimulation.'' Greater reductions 

were obtained, as in the present study, when 

visual fixation was employed. 

It is sometimes implied that the arousal factor 

represents a kind of artifact in habituation. 

Actually, the view propounded by Wendt'3 some 

years ago seems most appropriate; namely that 

there can be habituation to the test situation 

which produces a response decrement when 

alertness is not controlled. But, by simple 

instructions designed to relax a subject and 

reduce his mental activity, the same "response 

decrement" may be produced on the very first 

trial. • Hence, such a decline is not necessarily 

related to repeated vestibular stimulation. The 

changes that do occur as a result of repeated 

stimulation must be evaluated in terms of 

arousal level. 

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SUMMARY 

Forty unilateral caloric irrigations were 

administered in a habituation series to each of 

two groups of subjects. One group was tested 

in total darkness. Subjects in the second group 

were stimulated in illumination and actively 

attempted to control and suppress their eye 

movements by means of visual fixation. Preand posttests were administered ( always in 

total darkness ) in which both directions of 

response were elicited. In all cases, tasks were 

assigned to subjects to maintain alertness. The 

nystagmic reaction was altered as a result of 

the habituation series, but the change was 

different for the two groups. After one month 

of rest,· there was no apparent recovery of the 

response toward the pretest level for either 

group. Subjective reactions declined in intensity for both groups, but showed recovery after 

a one-month rest period. 

ACKNOWLEDGMENT 

The author is indebted to Tarea Lee and 

Joseph E. Duchon for their assistance in the 

conduct of this investigation. Additional assistance rendered by Ruth Ann Crain and Kathryn 

Quattlebaum is gratefully acknowledged. 

REFERENCES 

1. Lidvall, H. F.: Vertigo and Nystagmus Responses to 

Caloric Stimuli Repeated at Short Intervals. Acta 

Otolaryngol. 53: 33-44, 1961. 

5-3861 

2. Lidvall, H. F.: Vertigo and Nystagmus Responses to 

Caloric Stimuli Repeated at Short and Long Intervals. 

Acta Otolaryngol. 53: 507-518, 1961. 

3. Lidvall, H. F.: Mechanisms of Motion Sickness as 

Reflected in the Vertigo and Nystagmus Responses to 

Repeated Caloric Stimuli. Acta Otolaryngol. 55: 527-536, 

1962. 

4. Fluur, E. and Mendel, L.: Habituation, Efference 

and Vestibular Interplay. I. Monaural Caloric Habituation. 

Acta Otolaryngol. 55: 65-80, 1962. 

5. Fluur, E. and Mendel, L.: Habituation, Efference 

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6. Forssman, B., Henriksson, N. G., and Dolowitz, D. A.: 

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Laterotorsion and Vertigo in Man. Acta Otolaryngol. 56: 

663-674, 1963. 

7. Forssman, B.: Studies on Habituation of Vestibular 

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8. Lidvall, H. F.: Specific and Non-Specific Traits of 

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9. Collins, W. E.: Effects of Mental Set Upon Vestibular Nystagmus. ]. exper. Psychol. 63: 191-197, 1962. 

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11. Collins, W. E.: Task-Control of Arousal and the 

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Human Vestibular Responses. Acta Otolaryngol. Suppl. 

190, 34 pp., 1964. 

12. Guedry, F. E.: Visual Control of Habituation to 

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58: 377-389, 1964. 

13. Wendt, G. R.: Vestibular Functions. In S. S. 

Stevens (Ed.) Handbook of Experimental Psychology. 

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