SOME CHARACTERISTICS OF OPTOKINETIC 

EYE-MOVEMENT PATTERNS: A COMPARATIVE STUDY 

Approved by 

~~ 

William E. Collins, Ph.D. 

David J. Schroeder, Ph.D. 

Nancy Rice, B. A. 

Ruth Ann Mertens, M. S. 

Gail Kranz, B. S. 

CHIEF, CIVIL AEROMEDICAL INSTITUTE 

July 1970 

Department of Transportation 

Released by 

~AM> P. v. SiEGEL, M.D. 

FEDERAL AIR SURGEON 

FEDERAL AVIATION ADMINISTRATION 

Office of Aviation Medicine 
SOME CHARACTERISTICS OF OPTOKINETIC EYE-MOVEMENT PATTER

A COMPARATIVE STUDY 

1. Problem. 

Optokinetic nystagmus is an ocular rea~tion 

which occurs when a series of moving obJects 

crosses the visual field, or when an obser:er 

moves past a series of objects.30 The eyes mvohmtarily track the visual stimulus to the edge 

o£ the visual field or to the limit of comfortable 

gaze, and then make a rapid corrective movement 

in the opposite direction ;

3 they then fixate on a 

new stimulus, repeat the pattern of slow (followino-) and quick (return) movements, and b 21 p t thereby generate an ocular nystagmus. a -

terns of optokinetic nystagmus, although reportedly noted as early as 1825 by Purkinje while 

observing a crowd at a cavalry parade,12 have 

long been associated with transportation; Helmholtz is cited as having mentioned in an 1866 

article that the response was most readily seen 

when objects were observed from a train in 

motion.12 Indeed, one of the common terms used 

to describe this response was "railroad nystagmus" ;

1 21 that term is still used although the same 

phenomenon occurs in watching the external 

world from moving airplanes, cars, and other 

vehicles. The eye-movement pattern is similar 

to that produced by head movements which 

stimulate the vestibular system; in this ease, the 

pattern facilitates vision during ordinary earthbound activities, but can cause blurring of vision 

during "pilot's vertigo." 

In themselves, characteristics of optokinetic 

nystagmus are of significance. Wolfe, 32 for 

example, reported that a steady drop (adaptation) occurs in the following reaction of the 

human eye from the first few seconds of optoki-

--. The animals used for this experiment were lawfully 

acq uired and treated in accordance with the "Principles 

ot Laboratory Animal Care" issued by the Animal FariJJties Standards Committee of the Animal Care Panel, 

l'nited States Department of Health, Education, and 

Welfare, Public Health Service, March 1963. 

1 

netic stimulation throughout a 30-sec stim

period. If so, the eye, within this short a p

of time, would track at slower and slowe

locities. In addition, certain types of work 

been reported to produce an un~~sired oc

tional nystagmus. The most familiar of the

"miner's nystagmus"-a condition believed 

due to long periods of visual demand under_ 

poor lighting conditions. Less well-known I

occupational nystagmus found many years 

for train dispatchers ;

26 it appeared to be re

to job tasks which required continual move

of the head and eyes over a busy dispatc

train movement sheet, as well as continual m

ment of that sheet (sheet dimensions were 

feet by 2-3 feet, ruled into approximately 

small rectangles . related to stations, trains, 

crews). 

The relationship between characteristics o

optokinetic response to those of the vestib

reaction is also of importance. For examp

prominent feature of the vestibular nystag

elicited from cats by means of angular acce

tion is a secondary (reversed) response w

occurs shortly after stimulus termination. 

same eye-movement pattern occurs follow

optokinetic stimulation of rabbits28 and of c

In man secondary optokinetic reactions are 

siderabl~ less frequent and tend to be quite w

but many human subjects give vigorous secon

responses to vestibular stimulation. Moreo

optokinetic stimuli are frequently us~d to pro

calibration data for vestibular studies (part

larly with animals). Data published by Wol

althou o o-h not discussed in these terms, make q

tionable the use of this calibration proce

since he reported (a) steadily declining opt

netic responses from humans, and (b) 

increasing response from cats from the first 

seconds through the first 20 seconds of stim

tion. The latter confirmed a finding obtai

from rabbits by ter Braak. 2 
FIGURE 1. The CAM! optokinetic stimulator. 

2 
ome detail the characteristics of optokinetic 

~es ses from men and animals, particularly 

:yit.h regard to the questions of adaptation and 

possible directional differences. 

n. Method. 

St~ je cts. Human subjects comprised five men 

and five women, nine of whom were between the 

:

1ges of 21-29; one was age 37. All were labora.t.ory personnel. All but one man and one 

woman were right-handed. The seven African 

parrots were young-adult birds which had been 

captured wild approximately six months prior 

to testing. The 22 cats and six dogs were mature, young animals, farm-reared and of mixed 

breed. 

ApzJaratus. The optokinetic stimulator, located in a light-proof room comprised a steel 

drum supported by a steel frame (see Figure 1). 

The drum was four feet in diameter and two and 

one-half feet high, with its base 39 inches from 

the floor. The interior of the drum was painted 

white and to it were affixed vertical strips of 

black tape, each one inch in width and separated 

by two-inch intervals from adjoining strips. 

Each strip extended from the top to the base of 

I he drum. Two small spotlights, attached to the 

ceiling of the drum, provided illumination. A 

Century DC motor with a variable speed control 

permitted rotation of the drum at a constant 

an gular velocity of 24 o I sec ( 4 rpm) . 

A modified, adjustable chair was positioned 

nnder the drum at the center of the turning axis. 

'.['he chair had a removable back which permitted 

It~ conversion to an adjusta):>le platform for use 

With animals. An attachment provided a headl-est for human subjects. 

Rest1·aint. Cats and dogs were restrained by 

the technique described by Henriksson, Fernan-

~e z, a~1d Kohut,I 7 or by a modification of it. 9 

b tramt of Africa~ parrots was accomplished 

} a procedure descnbed elsewhere.u 

.Recording. Eye movements were recorded 

,,:~ h an Offner Type T Electroencephalograph. It] ] . 

1 

1 lllman subjects, surface electrodes were 

aped near the outer canthi for recording hori- "'llltal c 

1 ' omponents of eye movements, and above 

;nr below the right eye for recording vertical ~' Ponses S f 1 •• i tl · ur ace electrodes were also used 1 

cats for recording vertical ocular responses 

3 

around the left ocular orbit was shaved and the 

electrodes were taped in place. 7 Horizontal eye 

movements could be recorded from cats, dogs, 

and birds by means of needle electrodes. For 

the cats and dogs, the electrodes were inserted 

near the outer canthi of the eyes; for the birds, 

recording from each eye separately but simultaneously was accomplished by positioning electrodes on both sides of each eye. No attempt 

was made to record vertical nystagmus from the 

parrots or the dogs. 

Calibration and S coring. Human subjects 

were required to sweep their eyes from one 

marker to another on specially designed cards 

set at a standard distance (two feet) from each 

observer. The recorded displacement of the eyes 

was measured from the tracings in millimeters 

and converted to degrees/ mm to serve as a calibration factor for measurements of optokinetic 

nystagmus. Eye movements for calibration 

purposes were obtained prior to each trial. 

Optokinetic tracking during rotation of the 

drum served as the means of obtaining calibra-

• tion factors for the birds, the dogs, and the cats. 

Tracings obtained during specified periods of 

drum rotation were measured, calibration constants determined, and the rest of the record 

scored and converted to degrees of eye movement 

with these constatits.4 The calibration factor for 

each parrot was obtained (in an earlier study) 

from measurements of each tracing during the 

28-30 sec interval of stimulation, while for the 

dogs, the last available interval (16-18 sec) provided the calibration data. For cats, a block of 

10 consecutive seconds of "good" recording (i.e., 

with little or no artifact, no apparent voluntary 

eye movement, etc.) on a given trial was used to 

obtain calibration factors for that trial. 

All recordings were divided into 3-sec intervals 

for scoring purposes. Slow-phase nystagmus 

was scored by measuring the vertical distance, 

from peak to base line, of the slow-phase displacement of each nystagmic beat; these values 

were summed for each 3-sec, interval and converted to degrees as indicated above. Additionally, the number of beats within each interval 

was tabulated by simple counting procedures. 

P1·ocedu?·e. 

P ar1·ots and Dogs. Data from the parrots11 

and dogs10 were calculated from tracings obtained 

for calibration purposes in earlier studies. Only 
parrots were exposed to clockwise ( CW) drum 

rotation followed by counterclockwise ( CCW) 

stimulation after about one min of rest in illumination. Duration of the stimulus was always 

· at least 30 sec and frequently was longer. For 

dogs, a similar procedure was followed but only 

18 sec of response to CW stimulation was available for all six animals. During stimulation of 

parrots and dogs, the test room was in total 

darkness (to minimize possible distractions) 

with the exception of the miniature spotlights 

inside the optokinetic drum. At the conclusion 

of each trial, room lights were turned on and the 

drum was stopped. Afternystagmus in darkness 

was thus not recorded. 

Oats. One group of 10 cats received 30-sec 

periods of stimulation to both CW and CCW 

drum rotation. For hal£ of the animals, the CW 

condition occurred first; for the remaining five 

cats, CCW drum rotation was presented first. 

On a following day, five of the animals were 

tested for vertical optokinetic nystagmus for 

30-sec periods. Since the elicitation of vertical. 

responses required placing the animals on their 

sides, three cats were placed on· their right sides 

and exposed first to CW then to CCW drum 

rotation; they were then placed on their left 

sides and again given CW and CCW stimulation. 

The remaining two cats were given the same 

stimulation but were placed on their left sides 

first. Two additional trials were conducted with 

these five cats; in both cases, the animals were 

on their right sides and the drum was rotated 

CW.· During one such trial, the stimulus was 

applied for 15 sec; during the other, it was applied for 60 sec. 

A different group of 12 cats was exposed to 

elicitation of horizontal optokinetic nystagmus 

for 15-, 30-, 60-, and 120-sec stimulus periods, 

presented . successively and in that order on a 

single test day. CW drum rotation was used for 

six cats; CCW stimulation was applied to the 

remaining .six. 

Httmans. Horizontal optokinetic nystagmus 

was elicited from five human subjects by CW 

rotation of the drum for 15-, 30-, 60-, and 120-sec 

periods, presented successively and in that order 

on a single test day. These trials were followed 

by a 30-sec optokinetic stimulus with CCW drum 

rotation. For the remaining five subjects, CCW 

stimulation was applied for the four stimulus 

4 

cal optokinetic responses were obtain

way and for the same stimulus perio

separate day to avoid possible fatigu

General. The general procedure 

the cats and the humans was sim

strained cat was positioned with its 

the axis of drum rotation, either in 

position (horizontal nystagmus) or 

(vertical nystagmus). All lights 

guished immediately prior to the sta

The drum was set in motion and, w

the miniature spotlights inside the 

turned on. At the conclusion of 

period, the spotlights were turned 

drum was stopped. :&ecording cont

additional two min in total darknes

between trials comprised at least t

rest in the lighted room. Timing w

of a stopwatch. 

Similarly, humans were seated ei

with their heads centered beneath 

rotation of the drum (horizontal ny

with their heads tilted to the side 90

on the head rest (vertical nystag

latter arrangement required the sub

their usual sitting position to acco

lateral tilt of the head. Prior to e

calibration data were obtained as ou

The rest interval between trials wa

the lighted room. 

In all cases, attempts were made 

subjects alert throughout a trial

stimuli (e.g., hand clapping and sh

used with the dogs, birds, and c

subjects were verbally encouraged 

throughout each trial to maintain a

were told to maintain their gaze in 

of the black stripes (the black st

"closer" to most subjects than do

background) . 

III. Results. 

Dogs. Both slow-phase and fre

in 3-sec intervals show a general

output (Figure 2). The range of 

ever, was not particularly great. 

African paTrots. Tracings for 

were of good quality for both CW 

drum rotation. Plots of both slo

and response frequency (Figure 3

the nystagmic reaction increased fo
1e 

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w 40 Opto-Kinetic 0 4 Opto-Kinetic 0 Slow Phase Nystagmus ~ 

w Number Of Beats 

en • • 4 RPM CW >- • e 4 RPM CW l.&.J ::::> 30 ~ N=6 Dogs u 3 

l!) N=6 Dogs 

<t ~ 1- (.!) (/) <( >- 20 1-- 2 2 en 

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STIMULUS a:: ~ STIMULUS l.&.J 

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9 18 27 z 

9 18 27 

TIME IN SECONDS TIME IN SECONDS 

FIGURE 2. Slow-phase and frequency plots of horizontal optokinetic nystagmus for six dogs. 

!ires up through the first 12-18 sec of the 30-sec 

· tilllu.lus period. No striking difference in outPut between the two directions of response is 

e

1

1

·

1

dent and statistical tests (for correlated data) 

' lowed no significant directional differences in 

~~:a l output for either slow-phase (t=0.254) or 

I quency ( t= 1.895 · t of 2.57 required for .05 

ere] 0 f · ' Significance). 

5 

F or a better evaluation of the time-co:urse of 

the optokinetic response, data obtained from 

seven parrots (including the six noted above) 

during 45-sec periods of CW drum rotation were 

plotted (Figure 3). It is clear that the nystagmus builds to a peak between 12-30 sec and then 

shows some decline. The steady build-up of the 

response is of considerable magnitude; for fre-
..J 70 

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HORIZONTAL OPTO-KINETIC 

SLOW-PHASE NYSTAGMUS 

- 4 RPM cw o- -o 4 RPM ccw 

N = 6 Parrots 

END 

STIMULUS 

18 27 36 

60 

50 

40 

30 

20 

10 

9 

6 

5 

4 

HORIZONTAL OPTO-KINETIC 

SLOW-PH~SE NYSTAGMUS 

18 

..._ 4 RPM CW 

N = 7 Parrots 

27 36 

END 

STIMULUS 

45 5

:::::i!u 3 

(!)LLJ 

HORIZONTAL OPTO-KINETIC 3 

HORIZONTAL OPTO-KINETIC 

NUMBER OF BEATS <XCI) 

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0 

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9 

TIME 

NUMBER OF BEATS 

..._ 4 RPM CW 

o--o 4 RPM CCW 

N = 6 Parrots 

END STIMULUS 

18 27 36 

IN SECONDS 

2 ..._ 4 RPM CW 

N = 7 Parrots 

t::NO STIMULUS 

9 18 27 36 45 54 

TIME IN SECONDS 

FIGUllE 3. A comparison of the ocular responses of African parrots during 30 sec of OW and COW 

stimulation, and the time course of the response during 45 sec of stimulation. Note the extend

build-up of nystagmus similar to that obtained from dogs (compare with F igure 2). 

quency and for slow-phase data, the peak values 

are more than three and one-half times the output recorded during the first 3-sec interval. The 

decline, approximately 15 percent for both slow 

phase and frequency, may be only apoarent 

(i.e., a random variation) and probably -should 

be evaluated in terms of the results obtained 

from the cats over longer time periods. 

Oats : 1:1 orizontat Ny tagm~is . Ten cats were 

exposed to 30-sec optokinetic trials with both 

OW and COW drum rotation. A sample tracing 

6 

appears in F igure 4, and a plot of t

tiona} comparison is in F igure 5. 

figure and Table 1 provide three cl

information: (1) There is no statistic

cant directional difference in magnit

optokinetic response; (2) The nystao

a steady buiid-up throughout the st m~

( 3) Following stimulus termination, 

kinetic response declines steadily and 

to a reversed afternystagmus, i.e., to a 

optokinetic nystagmus (1n 17 of the 
:er 

of 

fihe 

;\'S 

:l ; 

o· 

l)' 

l')' 

.). 

I 

I 

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• 

CAT HORIZONTAL NYSTAGMUS 

~ 

CCW DRUM SPEED· 4 RPM 

20°._1 __ 

2 SE

~IGURE 4. A tracing of horizontal nystagmus elicited from a cat during and following 30 sec of optokinetic s

ulation. The tracing is continuous; . vertical bars demarcate the stimulus period. All lights were extingui

at the moment of stimulus termination. Note the early appearance of secondary nystagmus. 

With respect to the latter, there were no s1gniticailt directional differences in output (Table 1). 

Of 12 cats exposed to OW drum rotation for 

periods of 15-, 30-, 60-, and 120-sec, good records 

were obtained from all animals for the 60-sec 

stimulus, and from 11 animals each for the other 

stimuli. The mean slow-phase response and th~ · 

mean frequency, plotted in 3-sec intervals during 

the stimulus period, appear in Figures 6 and 7. 

Peak slow-phase response appears to require at 

least 24 sec of stimulation, whereas average peak 

frequency occurs after 15-21 sec of stimulation. 

In any event, there is a fairly prolonged build~up 

!)eriod and, after reaching a peak, the nystagmus 

IS variable but shows an inclination to decline in 

frequency after about one min of the 120-sec 

stimulus, whereas the slow-phase measures begin 

to decline at about that same time but recover 

to the original levels during the 90-120 sec phase 

of the stimulus. This combination of occurrences 

~or the two response measures may indicate the 

JnAuence of changes both in alertness of the anilllals and in their focus of gaze, as well as the 

Possibility of some adaptation. 

Afternystagmus (i.e., nystagmus recorded 

after stimulus termination) is plotted in Figure 

The last nine sec of the four 'stimulus periods 

are. also included for comparison purposes. Ex-

~~nation o.f these plots reveals: (1) only slight 

. erences 1n the output levels during the last 

0

1 e sec of the stimulus periods,· (2) a trend 

SJ • fi ' 

1

• · gill cant only for frequency) for the primary 

esponses during the 15-sec stimuli to decline 

tnore I 

s owly following stimulus termination, but 

7 

this may reflect differences in output level 

response tendency (build-up of nystagmus) d

ing the last 3-sec of the stimulus more than 

does an overall effect of stimulus duration; 

the magnitude of secondary nystagmus did 

appear to be influenced by stimulus durat

with the exception that there was a statistica

significant trend for the 15-sec stimulus (wh

was too short to permit primary nystagmus 

reach its peak) to yield the least slow-ph

secondary nystagmus; no other slow-phase co

parisons produced significant differences (Ta

1) and, following inspection of Figure 9, 

statistical tests were conducted for the frequen

data; Secondary nystagmus was present in 

of the 45 records. 

0 ats: Vertical Nystagmus. Vertical opto

netic nystagmus was obtained from five ca

However, it was possible · consistently to eli

a good ocular response in only one directio

i.e., with the fast-phase beating down (towa

the month). A tracing obtained from one anim

appears in Figure 9. The difference between t

two directions of eye movement is striking a

it occurs irrespective of the head position of t

cat; whether the animal is placed on its right 

its left side, drum rotation in the direction whi

would elicit up-beating nystagmus fails to pr

duce a consistent response of reasonable quali

in most cats, whereas good down-beating nysta

mus can be fairly readily obtained. 

Slow-phase and frequency measurements 

down-beating vertical nystagmus were plotte

for 15-sec and 60-sec stimulus durations (Figu
~ 70 -- 4 RPM CW 

u 

w o---0 4 RPM CCW 

Ul 60 N•IO CATS 

r<l ' 

a: 

w 50 !l. 

Ul 

w 40 w 

a: 

l!) 

w 30 9 

9 18 27 36 45 54 63 72 81 90 

HORIZONTAL OPTO-KINETIC 

NUMBER OF BEATS 

____. 4 RPM CW 

o---0 4 RPM CCW 

N•IO CATS 

9 18 27 36 45 54 63 72 81 90 

TIME IN SECONDS 

FIGURE 5. A comparison of the horizontal ocular responses of cats during and following 30 sec of OW 

and COW optokinetic stimulation. All lights were 

extinguished at the moment of stimulus termination. 

The same build-up of nystagmus occurs as found 

in the data from parrots and dogs (compare with 

Figur es 2 and 3). 

10). The response curves show some irregularity 

but give evidence of a build-up period and the 

possibility o·f a decline; however, the peak of 

the response does not . occur until after about 

45 sec of stimulation. Weak secondary nystagmus was observed on only one of the 10 possible 

occasions (following the 60-sec stimulus) . 

Httman Sttbjects: Horizontal Nystagmus. Human subjects showed no significant directional 

evident (Figure 11). With respect to the la

only five (three CW and two CCW) of the 

of 20 trials showed even slight evidence of 

ondary responses ; these occurrences were sp

among four subjects and were of such 

magnitude that they were not plotted. T

were no differences referable to sex or to h

edness. 

Plots depicting responses during the 15-

60-, and 120-sec stimuli were quite regul

appearance and showed neither a build-up p

nor a declining response during stimul

(Figure 12 and 13) with one exception; 

may be a tendency for the frequency of th

movements to be slightly higher during the 

two or three 3-sec intervals of a given stim

In examining afternystagmus (Figure 14

last nine sec of the average responses during 

of the four stimulus periods were also plo

no differences attributable to the stimulus 

tions are evident. However, there was a s

cant tendency for afternystagmus to be of g

magnitude following the longer stimulus 

tions (Table 2). The 15- and the 30-sec s

produced significantly less afternystagmus 

either the 60- or 120-sec stimuli ; no other 

parisons showed statistical significance. 

ondary nystagmus was again weak, an

scored (but not plotted) as possibly presen

ing only seven of the 40 trials; three of 

were following the 15-sec stimulus, two aft

30-sec stimulus, and two following 120 

optokinetic stimulation. 

8 

Human Subjects: Vertical Nystagmus. 

like the cats, human subjects gave con

vertical nystagmus to both directions of 

rotation. There was no statistically sign

difference between output levels (Table 

the two directions (Figure 15) . Seco

nystagmus was not obtained. Followin

30-sec stimuli, down-beating nystagmus 

considerably longer duration than the up-b

response, but this was attributable to two su

In plotting the time course of the vert

sponses during the four stimulus periods, 

slow-phase (Figure 16) nor frequency 

17) demonstrated a build-up or a declin

the same exception noted for the freque
ds 

or 

;es 

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70 

60 

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/0 HORIZONTAL OPTO-KINETIC 

SLOW-PHASE NYSTAGMUS 

o--o 15 sec (N=II Cats, 

• • 30 sec ( N= II Cats) 

.o.---6 60 sec ( N •12 C(]ts) 

• • 120 sec ( N= II Cats) 

w 30~----------------------------------------~-------------------- w 

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w 

50 

40 

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FiGURE 6. H 

9 18 27 36 45 54 63 72 81 90 99 108 117 126 

TIME IN SECONDS 

orizontal slow-phase responses from cats during four stimulus durations. A build-up period, so

variability, but no clear evidence of adaptation are evident. Drum rotation was 24° ;sec. 

9 
6 

5 

4 

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9 18 27 36 45 54 63 72 

TIME IN SECONDS 

HORIZONTAL OPTO-KINETI

NUMBER OF BEATS 

o---o 15 sec (N•II 

• • 30 sec (N• II 

t:.---t:. 60 sec (N • I2 

.Ao • 120 sec (N•II 

81 90 99 108 1

FIGURE 7. Frequency of horizontal nystagmus from cats during four stimulus durations. A build-up 

evident and some adaptation appears to occur during the 2-min stimulus. 

10 
60 

-...J 50 

(/)a: ~ ~w 40 ~~--

e>z <l1-u 30 (J)w >-(/) 

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:::::) 

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18 

I I I 

18 

HORIZONTAL OPTO-KINETIC 

AFTE.R RESPONSE 

SLOW-PHASE NYSTAGMUS 

o--o 15 sec (N•II Cats) 

------ 30 sec (N•II Cats) 

t:.--t:. 60 sec ( N • 12 Cats) .....__.._. 120 sec (N•II Cats) 

27 36 45 54 63 72 81 90 

TIME IN SECONDS 

I 

27 

HORIZONTAL OPTO-KINETIC 

AFTER-RESPONSE 

NUMBER OF BEATS 

o--o 15 sec CN= II Cats) 

._ 30 sec IN= II Cats) 

t:.- -t:. 60. sec (N • 12 Cats) 

........__.. 120 sec (N =II Cats) 

I I I I I I I I I I I I I I 

36 45 54 63 72 81 90 

TIME IN SECONDS 

I·'Jc uRJ;; 8. Horizontal afternystagmus (primary and secondary) from cats following the four durations of stimulation. The last nine sec of response during each stimulus are included. All lights were extinguished at the 

llloment of stimulus termination. The small differences in output among conditions during the last nine sec ot stimulation may reflect a slight adaptation effect. 

11 
,...4 

C1l 

+J+J 

~ ::l 0 

N+J 

"" $.10 ::l 

0 

::X:: 

ygp

Comparison 

I :>. { CW vs. CCW "" ""' ""' C1l 

p... (30-sec stimulus) a 

I 

ood { ~ 

0 :>. cw vs. ccw (J 

""' Q) C1l (30-sec stimulus) (f.l 

!I) 30 sec 

~ 15 vs. 

a! 

+J 

!I) 15 vs. 60 sec ~ 

""' Q) 

+J 

1.1-4 

< 15 vs. 120 sec 

:>. 

""' a! 

a 30 vs. 60 sec "" p... ""' 

,...4 

C1l 

+J 30 vs. 120 f?ec ~ 

0 

N 

"" ""' 0 60 vs. 120 sec 

::X:: 

15 vs. 30 sec 

!I) 

::l 

a 15 vs. 60 sec 

00 

C1l ,...4 +J C1l !I) 15 vs. 120 sec +J :>. ~z 

0 

N :>. 30 vs. 60 sec 

"" $.1 ""' C1l 

0'0 

::X:: ~ 30 vs. 120 sec 

0 

u 

Q) 

(/) 60 vs. 120 sec 

Measure 

Slow-phase 

Frequency 

Slow- phase 

Frequency 

Slow-phase 

Frequency 

Slow-phase 

Frequency 

Slow-phase 

Frequency 

Slow-phase 

Frequency 

Slow-phase 

Frequency 

Slow-phase 

Frequency 

Slow- phase 

Slow-phase 

Slow-phase 

Slow-phase 

Slow-phase 

Slow-phase 

12 

t 

0.011 

1.939 

0.028 

1.083 

2.893 

2.049 

3.173 

3.199 

1.758 

2.354 

2.524 

2.009 

0.159 

0.971 

0.215 

0.597 

3.359 

3.674 

3.144 

0.818 

0.495 

0.173 

Level o

Significa

.02 

.02 

.02 

.05 

.05 

.01 

.01 

,02 
( 

DRUM: 4 RPM 

ccw 

cw 

HEAD LEFT 

Fmm!E 9. Tracings of vertical nystagmus from a cat. Vertical bars demarcate the 60-sec stimulus. All ligh

were extinguished at the moment of stimulus termination. Up-beating nystagmus could not be elicited fo

sustained periods from most of the animals tested. Note the poor quality of the response during the fir

few sec. 
70 

60 

...J 

:; 50 

a: 

w 40 

0 

w 30 

(/) 

I 

10 20 

a: 

w 

n. 10 

(/) 

w 

w 

a: 

(!) 

w 

0 

70 

(/) 

"'"' ::l )j:>. 60 

(!) 

ct 

(/) 50 

>-

z 

w 

(/) 40 

ct 

:I: 

n. 30 

I 

3: 

0 

...J 20 

(/) 

10 

9 18 27 36 

VERTICAL OPTO-KINETIC 

SLOW-PHASE NYSTAGMUS 

HEAD RIGHT - DRUM CW 

15stc 

.A.---o\ 60 IIC 

45 54 63 72 

TIME IN SECONDS 

81 90 

...J 

:; 5 

a: 

w 

4 

0 

w (/) 3 

I 

10 

ffi 2 

n. 

(/) 

z 

w 

w 

> 

0 

uJ 

>-

w 

5 

(/) 

4 

II.. 

0 3 

a: 

w 

m 

2 

::l 

z 

9 

FIGURE 10. Vertical ocular responses from cats to two durations of 2

variable than that obtained for horizontal nystagmus, but appears 

were extinguished at the moment of stimulus termination. 
....J 

4 

50 en > ~ a:: 

2 w 

C> 1-

4 z 40 

1-

enu 

>-W 30 zen I 

w ('() 

en 

4 a:: 20 

:X: w 

a.. a.. 

3= en 10 

w 0 w ....J a:: en C> 

w 

0 

I I 

10 

en 

1- 9 

z 

w 

:::!! 

w 8 

> 

O....J 

:::!:4 

> Wa:: 

>-w Wt7 

()~ 6 

::!!u 

e>w 

4en 5 

1- I enrt'> 

>-

za:: 

w 

4 

I.La_ 

0 

a:: 3 

w 

(D 

:::!! 2 ::::> 

z 

HO RI ZONTAL OPTO-KINETIC 

SLOW-PHASE NYSTAGMUS 

-- 4 RPM cw 

o- -o 4 RPM ccw 

N = 10 HUMAN SUBJECTS 

~_L_L~L_~_L_LJ_L_~_L~~~~~~~~~~~6-6~ 

9 18 

I 

b, 

'o_o 

' 

9 18 

27 

27 

0 

" 

35 

36 

45 54 63 72 

HORIZONTAL OPTO-KINETIC 

NUMBER OF BEATS 

-- 4 RPM CW 

o--o 4 RPM CCW 

N = 10 HUMAN SUBJECTS 

81 90 

45 54 63 72 81 90 

TIME IN SECONDS 

f'IGtow 1] 

.,

4

: · A <:omparison of the horizontal ocular responses of human subjects during and following 30 sec 

~ t /set CW and CCW optokinetic stimulation. Note the sharp drop in output following stimulus termina

" Which moment all lights were extinguished. 

15 
50 

I 

/0 o, / 

...J I o/ 'o,o 

:; 40 

0::: 

w 

1-

z 50 -

u 

w 

(/) 

,:., 40 

0::: 

w 

CL 30 

(/) 

w w 

0::: 

l!) 

w 50 

a I 

(/) 40 :> 

l!) 

<I 

1- 50 (/) 

>-

z 

Li.J 40 (/) 

<I 

J: 

CL 

I 30 3: 

0 

...J 

(/) 

-6 6 

___ ,,_&....ll I,_ A.- --· _6-ll '6-l::r()( 

9 18 27 36 45 54 63 72 

TIME SECONDS 

FIGURE 12. Hor izontal slow-phase responses f r om human subjects durin

is relatively constant even during the 2-mln stimulus. D

------- ------ --

--
10 

0 

1\ 

I \ 0-0 

..J 9 I \ I 0 I 

4 0 

> 

a: 

w 8 

1-

z 

L) II 

w 

(/) 

I 

, 10 

a: 

w 

a. 

9 

(/) 

1-

z 

w 8 ~ 

w 

> 0 10 ~ 

9 18 27 36 45 54 63 72 

TIME IN SECONDS 

81 

HORIZONTAL OPTO-KINETIC 

NUMBER OF BEATS 

o---0 15 sec 

...--e 30 sec 

t:.---t:. 60 sec 

.tr----A 120 sec 

N=IO HUMAN SUBJECTS 

90 99 108 117 

~' 

JounE 13. Frequency of horizontal nystagmus from human subjects during four durations of 24°/ Sec stimulation. 

17 

1
~ w AFTER-RESPONSE (!) 1- 40 <t z SLOW- PHASE NYSTAGMUS 

1- o--o 15 sec (/) u 

>- w 30 -- z 30 (/) sec I 

w rt) 1:!.--1:!. 60 sec (/) 20 <t a:: ............... 120 sec :r w 

a.. a.. N = 10 HUMAN SUBJECTS I 10 ~ (/) 

w 0 w ...J a:: (/) (!) 

w 9 

0 

18 27 36 45 54 63 72 

TIME IN SECONDS 

10 

HORIZONTAL OPTO-KINETIC 

1 AFTER- RESPONSE 9 

NUMBER OF BEATS (/) 

1-

z o---o 15 sec 

• • w 8 30 

' 

sec 

w 

~ t.---6 60 sec ...J 

• > .. 120 <{ sec 0 > 7 

~ a:: 

w 

N•IO HUMAN SUBJECTS 

w 1-

>- z 6 w 

u u 

w I · (/) 5 

(!) I I 

<{ rt) 

1- II a:: (/) 4 

>- w II 

z a.. I 

lL 3 0 . 

a:: 

w 

m 2 

~ 

::::> 

z 

T I ME IN SECONDS 

FIGURE 14. Horizontal afternystagmus from human subjects following the four durations of stimulation; 

nine sec of response during each stimulus are included. The output of nystagmus drops sharply f

stimulus termination (when all lights were extinguished) and the amount of afternystagmus appears 

to the duration of optokinetic stimulation. 

18 
70 

_J 

<l: 

(f) > 60 

:::::> a:: ~ w (.!) I- VERT ICAL OPTO-KINETIC <l: z 50 

I- SLOW- PHASE NYSTAGMUS 

(f) u . >- w - 4 RPM cw 

z (f) 40 

I o- -o 4 RPM ccw w rt) 

(f) 

30 N = 10 HUMAN SUBJECTS <l: a:: 

I w a.. a.. 

3: (f) 20 w 0 w _J a:: (f) (.!) 10 w 

0 

_j 

9 18 27 36 45 54 63 72 81 

I I 

10 

(f) 

I- 9 z VERTICAL OPTO-KINETIC w 

~ NUMBER OF BEATS w 8 

> - 4 RPM cw 

0 _J 

~ <l: o- - o 4 RPM ccw 

> 7 w a:: N ~ 10 HUMAN SUBJECTS 

>- w w Iz 6 u 

~ u 

(.!) w 

<l: (f) 5 

I- I 

(f) rt) 

>-

z a:: 

w 4 

lJ.._ a.. 

0 

a:: 3 

w 

CD 

~ 2 :::::> 

z 

TIME IN SECONDS 

l 'w1· 

' HE l5. A comparison of the vertical ocular responses of human subjects during and following 30 sec of 

ant] CCW optokinetic stimulation. Note the sharp drop in output, similar to that obtained for horizontal n

~a~illlls, following stimulus termination (at which moment all lights were extingu ished). 'l'he longer r espo

0110\\'lllg CW stimulation is due to two subjects and, primarily, to only one of them. 

19 
70 

...J 60 

<( 

> 

0:: 

w 

r50 

z 

u 70 

w 

(/) 

f'() 60 

a:: 

w 

0.. 50 

(/) 

w 

w 70 a:: 

(!) 

w 

0 60 

-(/) 

::> 50 ~ 

(!) 

<( 

.... 70 (/) 

>-

z 

w 60 

(/) 

<( 

~ 

a.. 50 I 

~ 

0 40 ..J 

(/) 

o_o 0 

/ 

' 0 

\ / 

0 

~ 

(:;. (:;. \ 

't:.--~ I ""-t:.-t:;.-t:. (:;.-(:;. ' /(:;.\ -t:. t:! 't,.-t:.--tf / t:..._tf \ /(:;. 't:;.~ 

45 54 63 72 

TIME IN SECONDS 

81 

VERTICAL OPTO-KIN

SLOW- PHASE NYS

o---o 15 sec 

• • 30 sec t:.---t:. 60 sec 

.A. .A. 120 sec 

N = 10 HUMAN SUBJ

90 99 108 1

FIGURE 16. Vertical slow-phase responses from human subjects during four stimulus durations. No ada

effects are apparent. Drum speed was 24° / sec. 

20 
MUS 

s 

___,_j 

_._J ' 

126 

iOil 

..J 

4: 

> 

cr:: 

w 

1-

z 

l) 

w 

(f) 

I 

,.., 

cr:: 

w 

a.. 

(f) 

1-

z 

w 

10 

9 

8 

10 

9 

8 

7 

~ 10 

w 

> 

0 

~ 

w 

>-

w 8 

l) 

~ 

0 

' ' o, _,.o 

b"o 

VERTICAL OPTO-KINETIC 

NUMBER OF BEATS 

0---o 15 sec 

• • 30 sec 

t:.---1:>. 60 sec 

• .a. 120 sec 

N • 10 HUMAN SUBJECTS 

~ 7~~~~-L~~~~~~~~L-~~~~~_L~~~~~L-L-~~~~-L-L~~~~~~ 

~ (f) 

~ 10 

lL 

0 

9 

9 18 27 36 45 54 63 72 81 90 99 108 117 

TIME IN SECONDS 

I'IG('Jl!' 1~ ' ~~- . 1· I• requency of vertical nystagmus from human subjects during four durations of 24° ;sec stimulat

Ole eye movements appear to occur in the first few seconds of stimulation, but no clear adaptation eff

are apparent. 

21 
';1: 

en (.) 

>- w 

z en 

I 

w rt) 

en 

<( 0:: 

I w 

a.. a.. 

en 3:: w 

0 w ...J 0:: 

en (!) 

w 

0 

en 

Iz 

w 

~ w...J ><( 

o> 

~0:: w 

w I-

>- z 

w 

(.)(.) _w 

~en 

(!) I 

rt) 

~ enO:: 

>-w 

za.. 

lL. 

0 

40 

30 

20 

10 

8 

6 

5 

4 

3 

0:: 2 

w 

CD 

~ 

:::> 

z 

9 18 

9 18 

o--o 15 sec 

-- 30 sec 

6--6 60 sec 

..,_____... 120 sec 

N = 10 HUMAN SUBJECTS 

27 36 45 54 63 72 

TIME IN SECONDS 

VERTICAL OPTO-KINETIC 

AFTER-RESPONSE 

NUMBER OF BEATS 

o--o 15 sec ..____. 30 sec 

D.--D. 60 sec .....____.... 120 sec 

N= 10 HUMAN SUBJE~TS 

27 36 45 54 63 72 

TIME IN SECONDS 

FIGURE 18. Vertical afternystagmus from human subjects following the four durations of stimu

nine sec of response during each stimulus are included. The output of nystagmus drops shar

horizontal response) following stimulus termination (\Yhen all lights were extinguished). Alt

pears to be a tendency for the amount of afternystagnms to he greater following longer stimu

consistent statistical relationships \Yere obtained. 

22 
st 

Je 

p10 

1

1

the first two or t 1ree mterva s durmg each 

stimulus. 

As was the case with horizontal responses, 

combined plots of the final nine sec of the :four 

stimulus durations showed no effect o:f duration 

011 output levels (Figure 18). Afternystagmus 

acrain showed a tendency toward greater output 

f~llowing the longer stimulus durations, but the 

only statistically significant differences were between the 30- and 60-sec outputs (Table 2). 

Secondary nystagmus was weak, i:f it occurred 

CL t all, and may have been present during only 

four of the 40 trials; two of these were :following 

the 15-sec stimulus, and one each :following the 

60-sec and 120-sec stimuli. 

IV. Discussion. 

Anirnals. For the birds and the cats examined 

here, it is clear that: (a) there are no directional 

differences in output o:f horizontal optokinetic 

nystagmus; (b) the optokinetic response builds 

up throughout the initial 20-30 sec before reaching a relatively stable output level. The latter 

point also appears to be true :for dogs. 

The fact that the velocity o:f the slow-phase 

takes some time to reach a maximum value was 

noted by ter Braak2 in studies o:f rabbits. He 

attributed this to "central resistance" and compared it with mechanical friction (inertia). 

Whatever the cause, it is clear that, during the 

initial seconds o:f stimulation, horizontal optoki.netic nystagmus is not well developed (see 

Figure 4), i.e., the rhythmic pattern is not established. Then :for another period o:f several seconds, while the eye movements are rhythmical, 

the slow-phase displacement (or velocity) o:f the 

eye continues to increase until it finally levels off 

an:l remains relatively constant. The relationship .of t~e maximum eye velocity to the velocity 

of stJmuh cannot be ascertained by the data presented here; the calibration :factors were based 

~Pon the response to an arbitrarily selected por-

~IOI~ of the stimulus period. However, ter Braak2 

lllcli~ated that (with a freely movable eye) the 

(o t~tnnal) speed of the slow-phase is gene~ally a .httle less than that o:f the stimulus since the 

tunuli would no longer be effective i:f eye velocity 

and sti1 nu 1 1 · us ve oCity were the same. However 

under · 1 d' · ' t' speCia con Itwns, eye speed may exceed 

unulus speed. 2 It is possible that the build-up 

23 

the animal in gaining information about 

speed o:f movement o:f objects in the visual fi

i.e., that those periods provide error sign

which give the animal an accurate ("test") ba

for judging the speed of object movement. 

These results point to a clear methodolog

caution in using optokinetic data :from anim

to provide calibration factors for other measu

of eye movement (e.g., vestibular nystagmu

viz., the data used to derive the calibration :fa

must be from the relatively stable period o:f 

response (i.e., after at least the initial 10 sec 

stimulation). If other time periods are used 

are selected arbitrarily, (a) com pari sons fr

trial-to-trial or day-to-day will be made on 

accurate basis, and (b) the converted measu

ments will not reflect the true amount of 

movement. Other data20 provide an additio

caution; the relationship between eye velocity 

stimulus velocity is "not an unitary linear" 

in the cat. 

Upon termination of stimulation, in darkn

responses o:f the cat (and o:f rabbits2 ) de

gradually (primary afternystagmus) . ter Br

attributed this characteristic o:f the optokin

response to the same "central resistance" 

inertia that he used to account :for the build

o:f nystagmus during the initial seconds o:f st

ulation. In the cat (and in rabbits, at least a

prolonged optokinetic stimulation28 ) the af

nystagmus then gives way to a secondary 

versed) ocular nystagmus. These second

data :from the cat are strikingly reminiscent 

the characteristics of the vestibular eye-movem

response :following termination o:f an angu

acceleration. As noted by Wol:fe,32 the str

secondary nystagmus so readily obtained :foll

ing vestibular stimulation of the cat may be m

closely related to the activity of the optom

rather than the ·vestibular system. The res

are also pertinent to the "reflex rebound" 

optokinetic nystagmus (enhanced output t

change in the direction o:f drum rotation foll

ing 15-60 min o:f stimulation) and some appar

habituation reported :for turtles by Hayes, H

berg, and Hertzler.16 

O:f interest is the fact that neither the 

quency nor the amount of horizontal slow-ph

eye movement during the secondary phase 

consistently related to the duration o:f the st
Results of statistical comparisons between correlated optoki

nystagmus scores for human subjects (N = 10). 

L

ComEarison Measure t Sig

.-l 

ell 

.j.J 

.j.J 

II { r:: ;:I 

0 cw vs. ccw Slow-phase 0.354 

p. N .j.J (30-sec stimulus) Frequency 1.567 

..... ;::1 

1-10 

0 

:I:: 

15 vs. 30 sec Slow-phase 0.139 

Ul Frequency 0.908 

;::1 

fib 15 vs. 60 sec Slow-phase 3.021 

ell Frequency 3.547 

.j.J 

Ul 

>. 

s:: 15 vs. -120 sec Slow-phase 2.981 

""' QJ 

Frequency 3.050 

.j.J 

~ 

< 

.-l 30 vs. 60 sec Slow-phase 2.975 

ell Frequency 2.909 

.j.J 

s:: 

0 

N 30 vs. 120 sec Slow-phase 3.024 

..... 

""' Frequency 2.871 

0 

::z:: 

60 vs. 120 sec Slow-phase 2.159 

Frequency 1.784 

.-l { 

ell .j.J cw vs. ccw Slow-phase 1.483 u ;::1 

..... p. (30-sec stimulus) Frequency 1.274 .j.J .j.J 

""' ;::1 QJO 

:> 

15 vs. 30 sec Slow-phase 1.272 

Frequency 1.377 

Ul 

;::1 15 vs. 60 sec Slow-phase 2.213 13 

bO 

Frequency 2.113 ell 

.j.J 

Ul 

>. 15 vs. 120 sec Slow-phase 1.824 s:: 

""' QJ 

.j.J Frequency 1.925 ~ 

< 30 vs. 60 sec Slow-phase 2. 775 

.-1 

ell Frequency 

2.345 u 

..... 

.j.J 30 vs. 120 Slow-phase ""' sec 

QJ 2.047 

:> Frequency 1.671 

60 vs.l20 sec Slow-phase 0.016 

Frequency 0.250 

24 
rhe. significantly lower slow-phase secondary 

out put for the 15-sec stimulus probably can be 

11

tribntecl to the fact that the peak output level 

for the primary nystagmus had not been reached 

t>rfn re the stimulus was terminated. 

r ertical optokinetic responses from the cat also 

,ho1red evidence of a build-up period and a 

•• r:1dnal decay after stimulus termination. Howre r, it was more difficult to . determine the time-

,.0n rse characteristics of the vertical eye movements; they were less regular than horizontal 

nystagmus and were obtained with the animals 

in an undesirable position (on their sides). It is 

possi ble that the vertical response builds up 

throughout the initial 45 sec of optokinetic 

slimnla.tion and then begins to decay ( adaptation) during further periods of stimulation. 

Of more interest, however, was the inability consistently to evoke an up-beating nystagmus from 

the cats; only down-beating (i.e., toward the 

mouth) eye movements could be uniformly 

elicited regardless of which eye was used for 

recording, or upon which side the animal was 

placed, or in which direction the drum was 

turned. We have no explanation for this directional difference although Krieger and Bender22 

r·eported that vertical optokinetic reactions from 

monkeys were "less apparent" when the fast 

phase beat from head to foot (downward). This 

latter finding is the opposite of what we have 

observed in cats; to make certain of our findings, 

we have supplemented our electronystagmographic recordings with direct visual observation 

both in this study and in an earlier one8 in which 

lh.e same results were obtained from a group of 

lb cats. Asymmetries in vertical nystagmus have 

also been reported for humans. 

llwnans. Like the animals human subjects 

:!ro,'.'ed no significant differen~e between rightheatmg and left-beating horizontal nystagmus 

an cl there was no significant adaptation apparent fo r resr l . . r . )onses astmg as long as two mm. These 

'

',':d,ngs do not agree with those reported by olfe 32 W I . f . · e 1ave no explanatiOn for the lack 0 d t' lrec 10nal preponderance found here and the 

llla rked 1 . 10 sow-phase asymmetry (approxrmately 

per cent more displacement during OW as I'IJI))[)[\' d ' \\'o ]f~ re wrth COW dr~m rotation) ~1oted by 

' other than possrble chance drfferences 

llrtonro· tl b ' ,

1 _

1 . o 1e su Ject populations used. Other lluJes e.g 8 13 23 . 

• ' · • 25 also have not found consistent 

25 

g 

p

parent "marked adaptation" shown by Wolfe's 

subjects (a steady slow-phase decline from the 

first five sec period of stimulation through the 

25-30 sec period, comprising a reduction of approximately 20-25 per cent) is probably due to 

alertness factors and changes in gaze. Char

acteristics of optokinetic nystagmus are known 

to be affected by the method of gaze used by the 

observer, e.g., "look" vs. "stare" nystagmus. 2 19 

However, our experience indicates that even 

though active tracking of a stripe ("look" 

nystagmus) may not occur, there is a tendency 

over time for the focus of gaze to change, i.e., the 

plane of visual fixation appears to shift. When 

subjects are instructed to maintain their gaze in 

the "plane" of the black stripes (the white background is frequently perceived as more distan

in our device), and are encouraged to maintain 

a state of alertness, no "adaptation" occurs, a

least for the periods of stimulation used here

Figure 19 depicts tracings obtained under in

structions to be alert (supplemented by verba

encouragement during the trial) and instruction

to relax while staring in the plane of the black 

stripes. Similar results have been reported in 

recording vestibular nystagmus,5 6 as well a

vertical optokinetic responses.29 Moreover, Mack

ensen24 has noted that, during the course of six 

min of optokinetic stimulation, the amplitude o

nystagmus increases (particularly after two min) 

to a marked degree while frequency declines only 

slightly. 

Unlike the animals, there were obtained from 

the human subjects (a) no statistically significan

directional differences in the overall output o

vertical nystagmus, (b) no build-up period fo

slow-phase nystagmus to reach its maximal level

(c) a sharp drop in nystagmic output (in dark

ness) following stimulus termination, (d) a pro

longed primary afternystagmus which was o

greater magnitude following longer durations o

optokinetic stimulation, (e) almost no secondary 

nystagmus, (f) a tendency for both horizonta

and (particularly) vertical nystagmus to show 

a higher frequency of eye movements during the 

first few sec of stimulation. Several of thes

findings require comment. 

Although there were no significant group dif

ferences between up-beating and down-beating 

vertical nystagmus, there were several striking 

directional differences for individual subject
! ' 

ALERT 

6 RPM 

RELAXED 

ALERT 

~'\,.. 

15·------"'; 

fl.. 

15~ 

SUBJECT WEC 

FIGURE 19. Tracings of horizontal nystagmus from a human subject given instructions to focus in the plane 

black stripes and either to (a) maintain alertness (verbal encouragement was also given on these "alert" 

or (b) relax but maintain focus. CW stimuli were 30 sec in duration (demarcated by the vertical bar

all lights were extinguished at the moment of stimul us termination. Clear "adaptation" is evident duri

4 rpm stimulus under the relaxed condition; the alert condition yielded brisk responses to both stimulu

(Figure 20) . A mar keel asymmetry in vertical 

responses from humans has been noted before ;

29 

in one sample of 20 subjects, the frequency of 

eye movements tended to be higher more often 

in the up-beating direction. In our sample, six 

of the 10 subjects showed an up-beating preponderance, but three of these differed directionally by less than 10 per cent; of the four subjects 

who had higher-frequency nystagmus in the 

down-beating · direction, only two had directional 

differences exceeding 10 per cent. It is clear that, 

in at least some apparently normal subjects, a 

marked directional difference in frequency of 

vertical optokinetic nystagmus may occur. Directional differences in vertical nystagmus of 

vestibular ongm appear in the observation by 

26 

Hixson and Niven18 that a vestibular sti

which induces vertical nystagmus with fast-

down causes blurring (loss of visual acuity

longer periods than an equl.valent vest

stimulus which produces vertical eye move

with fast-phase up. Similarly, Guedry 

Benson1 5 noted higher-frequency vestibula

tagrnus in a down-beating direction in dark

introduction of a visual task during a v

vestibular nystagmus did not affect the freq

of down-beating nystagmus, but it clear

clucecl the frequency of up-beating nystagm

The failure to obtain clear secondary n

mus may be partly a function of the sti

durations used in this study. Macke

reported that "in a number of healthy pe
/ 

.he 

Is) 

nd 

.he 

es. 

us 

156 

·or 

nr 

tts 

nd 

iS· 

;s· 

:a! 

c)" 

:e· 

1S 

VERTICAL NYSTAGMUS 

cw J1 

ccw J1 

SUBJECT RAM 

FIG I"HE 20. Tracings of vertical nystagmus from a human subject. Vertical bars demarcate the 30-sec periods 

24° ;sec stimulation. The subject was positioned with her head tilted 90° to the right. A clear asymme

lletween the characteristics of the up-beating and down-beating r esponses is evident. Two additional subje

showed these same marked differences, while two .others demonstrated them in the opposite direction. 

:1 secondary nystagmus was elicited following six 

min of optokinetic stimulation. Other investign tors27 obtained secondary optokinetic nystagmus from all four of their subjects, but their 

test technique was different; they used a constant 

angul ar acceleration of their drum (rather than 

:t constant velocity) and applied a 1 o / sec2 stimulus for two min (the final speed of the drum 

was thus 120° / sec). In any event, the secondary 

msponse is not as characteristic a feature o£ 

human optokinetic reactions as it is of cats. Further, human secondary nystagmus appears to be 

111o re readily elicitable following angular acr·clerat.ion than it does following periods o£ 

(constant) optokinetic stimulation o£ "reasonable" duration (up to two min) . 

A ~nal point concerns the relationship o£ eye 1 eloc1ty to stimulus velocity. Wendt31 presented 

<lat:t (obtained durino- harmonic rotatory stim-

•llation of human subj~cts with vision permitted) 

wl 11] · a· C l lll 1cated that optokinetic eye speed was 

about 80 per cent of stimulus speed. Our vertical 

eye movement data ao-ree with this figure but ou r ] · 0 · ' lonzontal eye-movements were only about 

1

-.o per cent of stimulus speed. It is conceivable 

ha t the characteristics o£ the stimulus field 

t ~" spa . f . . _.,..., ' cmg o st1muh and type of moving ' 1linuh ) . IS as well as stimulus speed may have a '' "nifi c , ~I ant effect on the eye velocity. There are •I •e t· p 'b· .. oss1 1htles. Calibration techniques which 1

11 ol re · sweepmg the eyes between two markers 

are reported to produce different calibrati

factors with changes in the distance between t

subject and the markers (apparently due 

accommodation -con vergence differences) , ev

though the visual angle is the same.14 This mig

have affected the horizontal nystagmus data 

the present study since the electrodes were at 

outer canthi of the two eyes ; it is less likely 

have affected the vertical nystagmus data wh

recordings were obtained £rom only one eye. 

addition, the scoring technique used in this stu

ignored (for practical purposes) the time s

ments taken up by the fast phases of the n

tagmic movements; this approach would prod

some underestimation of the slow-phase veloc

27 

V. Summary. 

Optokinetic stimulation of dogs, parrots, 

cats showed that both slow-phase displacem

and frequency of eye movements increased d

ing the initial ·18 sec or more o£ stimula

before leveling off. There was no signific

difference between right-beating and left-bea

responses. Cats were studied more extensiv

and showed no clear adaptation effects 

stimuli up to two min in duration. Cats 

displayed a smoothly declining afternystag

(in the dark) following stimulus terminat

this response consistently gave way to a second

nystagmus, the magnitude of which did not s
down-beating direction. Human subjects showed 

no consistent directional differences in either 

horizontal or vertical optokinetic nystagmus but 

differed from the cats in that no build-up period 

tions of stimulation, and secondary resp

· d kS 

were both mfrequent an wea . orne st

but apparently normal asymmetries in th

tical responses of humans were noted. 

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29