NASA Technical Memorandum 102 157 

Visual Suppression of the Vestibulo-ocular 

Reflex During Space Flight 

John J. Uri 

GE Government Services 

Houston, Texas 

William E. Thornton, and Sam L. Pool 

Lyndon B. Johnson Space Center 

Houston, Texas 

Thomas P. Moore 

Methodist Hospital of Indiana 

Indianapolis, Indiana 
Contents 

Section Page 

Abstract ............................................................................. 1 

Introduction .......................................................................... 1 

Methods ............................................................................. 1 

Results .............................................................................. 2 

Discussion ............................................................................ 4 

References ............................................................................ 5 

Appendix-DataTables .................................................................. 7 

... 

111 
Tables 

Table Page 

1 Schedule of records obtained .......................................................... 2 

2 Summary of statistical results for 12-subject population ....................................... 3 

A1 Preflight VOR suppression nystagmus data.. .............................................. 7 

A3 Mean amplitude of nystagmus beats, in degrees ............................................. 8 

A4 Cumulative nystagmus amplitude, in degrees ............................................... 8 

A2 Frequency of nystagmus beats per two head oscillation cycles ................................... 8 

Figures 

Figure Page 

1 

2 

3 

Subject performing VOR-suppression test. The target for visual fixation can be seen at far left, 

and the pantograph mounting for the head position potentiometer is at upper right. ................... 2 An example of a typical in-flight recording of VOR suppression ................................. 3 Preflight and in-flight mean and S.D. of the number of beats of nystagmus and the 

cumulative nystagmus amplitude during two head oscillation cycles. Differences between SMS 

and non-SMS populations are also shown. IN1 and IN2 refer to early and late inflight periods, 

respectively ....................................................................... 3 

iv 
Visual suppression of the vestibulo-ocular reflex during space flight 

Abstract 

Visual suppression of the vestibulo-ocular reflex was 

studied in 16 subjects on four Space Shuttle missions. 

Eye movements were recorded by electro-oculography 

while subjects fixated a head-mounted target during active 

sinusoidal head oscillation at 0.3 Hz. Adequacy of 

suppression was evaluated by the number of nystagmus 

beats, the mean amplitude of each beat, and the 

cumulative amplitude of nystagmus during two head 

oscillation cycles. Vestibulo-ocular reflex suppression was 

unaffected by space flight. Subjects with space motion 

sickness during flight had significantly more nystagmus 

beats than unaffected individuals. These susceptible 

subjects also tended to have morenystagmus beats before 

flight. 

Introduction 

A comprehensive investigation of neurologic adaptation 

to space flight was undertaken as a joint NASA Johnson 

Space Center Flight Operations Directorate and Medical 

Sciences Division project. Among other studies, vestibular 

and optokinetic experiments were performed on Shuttle 

missions STS-4 through 8 (1982-3) (1). This report 

presents the results of studies on visual suppression of 

the horizontal vestibulo-ocular reflex (VOR). Results 

from a few subjects in this series have been reported 

elsewhere (2,3,4), but this report presents the complete 

study. Preflight and in-flight measurements were obtained 

from 12 subjects, and preflight and postflight data from 

an additional four subjects. 

The VOR compensates for head movement to permit 

the eyes to maintain foveal fixation on stationary objects 

in the environment (5). Moving objects in the environment 

are often tracked with head movements during which the 

eyes are held stable relative to the head. Under these 

conditions the VOR must be suppressed to prevent loss 

of visual fixation on the target (6). Suppression of the 

VOR is achieved primarily by the visual smooth pursuit 

system, at least under conditions where that system is 

effective (e.g., predictable target motion at low-frequency 

and amplitude) (7), although there is also evidence for 

direct suppression of the VOR by the cerebellar flocculus 

Suppression of the VOR has been well characterized 

in the terrestrial environment (7-19). A common study 

(8). 

method is to have subjects track a target that, during 

head motion, moves with the same angular velocity as 

the head. Eye and head movements are recorded and 

graphically displayed. Usually, amplitude or velocity of 

eye and head movements are compared and the gain is 

determined. During either active or passive sinusoidal 

head oscillations at frequencies below 0.5 Hz, VOR 

suppression gain is often reported to be less than 0.10 

(7,9,12,13,15-19). Another method of assessing visual 

suppression of the VOR is to measure the total amplitude 

of nystagmus fast phases produced over a given duration 

of head oscillation (IO). 

Subsequent to our studies, VOR suppression has also 

been examined during space flight (20,21). Using active 

horizontal head oscillation at 0.25 Hz as the stimulus 

in one subject on STSJlG, Vitville, et a1 (20) reported 

in-flight gains of 0.09 and 0.10 on mission days 4 and 

7, respectively, and a gain of 0.085 one day after landing. 

Although no preflight measurements were reported, they 

concluded that VOR suppression was not affected by 

space flight. 

Benson and Vihille (21) reported preflight and 

postflight VOR suppression gains of a single Spacelab1 crewmember. Preflight mean was 0.38, while gain on 

the first postlanding day was 0.23, significantly (p=0.05) 

lower than preflight. Subsequent postflight values were 

0.44. The methodology differed in that passive head 

oscillation at 1 Hz was the stimulus but with the head 

axis displaced 1 m from the rotation axis. 

Methods 

Subjects. The sixteen volunteer subjects for this study 

were all professional NASA astronauts, fifteen males and 

one female ranging in age from 32 to 54 years. All had 

experience in high-performance jet aircraft and three had 

prior space flight experience. There were no known visual 

or vestibular abnormalities, other than presbyopia 

corrected to normal acuity by glasses. Consent was 

obtained from each subject after explanation and 

demonstration of the procedure. On three of the flights, 

a physician crewmember administered the test. 

Eye and head position recording. Horizontal eye 

movements were recorded using conventional electrooculography (EOG) (22). One cm Ag-AgCI electrodes 

were located at the lateral canthi with a mid-forehead 

I 
'- **I ! 

i 
investigators attempt to assign a gain value to VOR 

suppression, in the large majority of our records no 

sinusoidal eye movement patterns wereevident, and there 

was insufficient eye movement to attempt to reconstruct 

a sinusoid. Instead, we used a modified method of 

Dichgans, et a1 (IO) and recorded the number of nystagmus 

movements (nystagmus frequency) and their mean 

amplitude during two complete head oscillations and then 

calculated the total nystagmus amplitude for that duration. 

Consistent scheduling of experiments among all 

subjects was not possible due to in-flight operational 

constraints. We therefore combined in-flight measurements 

into two epochs, early (Mission Day [MD] 1-2) and late 

(MD 3-6). The early epoch corresponds to the period of 

symptoms of space motion sickness (SMS) in all affected 

subjects, allowing comparisons between affected and nonaffected subjects. Independent t-tests were used to compare 

preflight and in-flight measurements, as well as SMS 

susceptible and non-susceptible populations. 

Figure 1.- Subject performing VOR suppression test. The target 

for visual fixation can be seen at far left, and the pantograph 

mounting for the head position potentiometer is at upper right. 

ground. Amplification and recording had an overall 

frequency response of 0.05 to 70 Hz (3 dB points). Eye 

position could be determined to <2% accuracy. EOG was 

calibrated prior to each study by having the subject fixate 

five high-intensity light-emitting diode (LED) targets 

located at visual angles of Oo, f15" and f30° (STS5 and 6), or 0", *IO" and f20" (STS-7 and 8). 

Head position was recorded by a precision (0.1% 

error) potentiometer mounted in a pantograph system 

that allowed f5 cm translation motion without detectable 

output. The potentiometer was coupled to the subject's 

head by a closely-fitting fabric helmet. Overall accuracy 

was on the order of 2%. 

Data were either transmitted from the spacecraft via 

a DC-100 Hz digital system with eight bit resolution or 

recorded onboard on a miniature analog magnetic tape 

system, then transcribed to 100 mm per channel width 

graphic record at 10 mm sed. 

Protocol. The target used for VOR suppression studies 

was a white 5 mm diameter sphere on a 42cm lightweight 

boom on the eyes' axis, attached to the head with a cap 

and chin strap (figure 1). All measurements were recorded 

with the subject restrained in a crew seat or equivalent. 

On earth, the subjects were seated with a vertical gravity 

vector. Subjects were trained to make horizontal 

sinusoidal head oscillations at an amplitude of f30 

degrees and frequency of 0.3 Hz without external pacing 

cues. They were requested to fixate on the head-mounted 

target during at least five head oscillations. The visual 

background was variable. 

Results 

Measurements were obtained from 16 subjects on Shuttle 

flights STS 5 through 8, with a total of 52 records preflight, 

35 during space flight, and 15 postflight (table 1). None 

of the subjects reported any subjective visual or 

oculomotor disturbances during the flights. The six 

subjects marked with an asterisk exhibited symptoms of 

Table 1.- Schedule of records obtained 

~ ~~ ~~~ 

Flight/ Preflight In-flight Mission Day Postflight 

Subject 

1 2 3 4 5 6 R+OD R+IOD 

STS5 1 2 1 I 1 

2* 3 I 

STS6 3 I 1 I 1 

4* I 1 1 

5 1 I 1 1 

62 I I 1 

sTs7 7 2 11 

8* 2 11 1 

92 11 1 

IO I 1 

11* 4 112111 2 

STS8 12 6 1 I I 

13 5 1 1 1 1 

14* 5 I1 1 1 

15 6 1 I 1 

Data reduction and analysis. Data were manually 16* 9 I I I 

reduced from the graphic records. Although most 

2 
EYE POSITION (EOG) 

I SUSCEPTIBLE TO SMS 

0 ALL SUBJECTS 

NON SUSCEPTIBLE TO SMS 

T 

16 0 

a 

W 2 12.0 

12 ' 80 

4.0 

n 

Figure 2.- An example of a typical in-flight recording of VOR 

suppression. 

SMS on MD I and 2; six records were obtained during 

their symptomatic period. A typical in-flight recording 

is shown in figure 2. 

Twelve of the subjects recorded data during both 

early and late flight phases. Mean changes from preflight 

in the number of nystagmus movements and their total 

amplitude during two complete head oscillations are 

shown in figure 3. A comparison between SMS and nonSMS populations is also shown. 

No significant changes from preflight in either the 

number of nystagmus movements or their total amplitude 

were seen during space flight (table 2). However, subjects 

with SMS had significantly more nystagmus beats than 

non-susceptible subjects during both in-flight periods 

(~4.023 early and p=0.002 late), with no significant 

difference between the two groups in total nystagmus 

amplitude. Mean amplitude of each nystagmus movement 

was not different between the two groups and did not 

change with space flight (see data in Appendix Table A3). 

By pooling all in-flight data, measurements from an 

additional three subjects were included in a further analysis. 

In this population of 15 subjects, five with SMS, no 

significant changes from preflight were seen in nystagmus 

frequency or total amplitude. During flight, the SMS 

subjects had greater nystagmus frequency (p4.004) and 

total amplitude (~4.054) than the non-SMS group. 

Postflight measurements on the day of landing were 

obtained from a population of eight subjects, all but one 

T 

I 

" 

PRE IN1 IN2 PRE IN 1 IN2 

NUMBER OF NYSTAGMUS CUMULATIVE NYSTAGMUS i 

BEATS AMPLITUDE 

Figure 3.- Preflight and in-flight mean and S.D. of the number 

of beats of nystagmus and the cumulative nystagmus amplitude 

during two head oscillation cycles. Differences between SMS 

and non-SMS populations are also shown. IN1 and IN2 refer 

to early and late inflight periods, respectively. 

of whom also had in-flight data. Nystagmus frequency 

was unchanged from preflight, but the total amplitude 

was decreased (p=0.05). 

Table 2.- Summary of statistical results 

for 12-subject population 

Nystagmus frequency Mean f SD . P 

Pre vs. In-flight I 

Pre vs. In-flight 2 

Preflight 14.7 f 5.0 vs. 8.8 f 4.0 0.067 

In-flight 1 13.5 f 7.1 vs. 5.5 f 3.4 0.023 

In-flight2 15.1 f 3.8 vs. 7.1 f 4.6 0.002 

10.7 f5.2 vs. 8.6 f 6.7 

10 f 5.2 vs. 10.9 f 5.8 

0.466 

0.948 

SMSvs.non-SMS 

Nystagmus amplitude Mean f SD P ~~ ~ ~~ 

Pre vs. In-flight 2 

Pre vs. In-flight 2 

28.1 f 15.2 vs 22.8 f 15.8 

28.1 f 15.2 vs. 25.7 f 16.4 

0.410 

0.537 

SMS vs.non-SMS 

Preflight 37.9 f 16.7 vs. 23.3 f 11.7 0.137 

In-flight 1 31.3 f 16.9 vs. 16.5 f 11.3 0.095 

In-flight 2 34.3 f 13.5 vs. 19.2 f 15.3 0.164 

3 
When comparing preflight data from SMS susceptible 

subjects with non-susceptible subjects, nystagmus 

frequency and total amplitude tended to be greater in the 

susceptible group, although the differences were not 

statistically significant (p=0.067 and 0.137, respectively). 

In a retrospective analysis of preflight data from the 16 

subjects, individuals with more than 10 beats of nystagmus 

per two head oscillation cycles were “predicted” to have 

SMS during space flight, while those with less than 10 

beats were “predicted” to be SMS-free (frequency test). 

Similarly, subjects with 30 degrees or more of cumulative 

nystagmus amplitude were assigned to the SMS category, 

and subjects with less than 30 degrees to the non-SMS 

category (total amplitude test). Overall, 11 of the 16 

subjects were correctly assigned by the frequency method 

and 12 of 16 by the total amplitude method. Specificity 

and sensitivity of the frequency test were 67% and 80%, 

and 67% and 70%, for the total amplitude test, respectively. 

Discussion 

This study found that visual suppression of the VOR was 

not affected by space flight. In addition, subjects with SMS 

had a higher frequency of nystagmus during space flight 

than subjects who did not have SMS. Susceptible subjects 

also had a tendency toward higher nystagmus frequency 

before space flight. Postflight, although nystagmus 

frequency was unchanged from preflight, the total 

amplitude was decreased. 

Most investigators quantify suppression of the VOR 

by computing gain (7,9,11-19). However, many of the EOG 

tracings during our VOR suppression studies lacked a 

sinusoidal pattern, and the limited nystagmus that was 

present did not permit adequate reconstruction of a 

sinusoid (see figure 2). In other words, VOR suppression 

was essentially complete and any gain calculation would 

have been close to zero. 

During incomplete VOR suppression, the observed 

nystagmus represents errors induced by the VOR that take 

the eyes off the target and subsequent corrections by 

saccades to reacquire the target (23). We therefore chose 

to evaluate the adequacy of VOR suppression by 

determining the number of beats of nystagmus, the mean 

amplitude of each beat, and the cumulative amplitude of 

nystagmus summated over two complete head oscillation 

cycles. 

The clinical and functional significance of our results 

is unclear. That VOR suppression is unaffected by space 

flight agrees with the results from the other in-fight study 

(20). However, VOR suppression may be less complete 

in individuals with SMS both during their symptomatic 

period and following recovery. This did not seem to affect 

any of the crewmembers, all of whom were able to execute 

without difficulty a variety of tasks requiring good visual 

and oculomotor performance. 

Are the observed differences in VOR suppression a 

cause or an effect of SMS? On the one hand, retinal 

image slip due to inappropriate eye movements during 

head motion can elicit oscillopsia and cause motion 

sickness-like symptoms (24). Abnormal visual-vestibular 

interaction in weightlessness has been postulated to be 

a cause of SMS (1,25,26). However, it is unlikely that 

the incomplete VOR suppression seen in our study was 

a cause of SMS. First, the magnitude of the retinal slips 

during our studies was such that appreciable oscillopsia 

was unlikely (27). Indeed, in response to detailed 

questioning, none of the affected crewmembers reported 

it at any time. And second, the increased nystagmus 

frequency during VOR suppression persisted even after 

the affected subjects had recovered from SMS. 

On the other hand, the mechanism of SMS is 

presumed to be of central nervous system (CNS) origin 

(1,25,26). Although a variety of CNS disturbances have 

been shown to cause impairment of VOR suppression 

(10,28,29,30), it is unlikely that any gross pathology was 

present in any of the subjects in this study. Could more 

subtle changes, such as altered CNS function caused by 

the cephalad redistribution of fluids in weightlessness (3 1) 

be responsible? This hypothesis is unlikely, since the fluid 

shift involves all individuals whether affected by SMS 

or not (32), and other space flight studies of CNS function 

have not shown any changes (33). 

An intriguing result of this study was the finding 

that subjects who developed SMS in-flight tended to have 

more nystagmus during preflight VOR suppression tests 

than non-susceptible subjects. With regard to total 

nystagmus amplitude, this preflight difference correctly 

predicted the in-flight SMS status of 75% of-the subjects. 

Although this is the best single predicto-r for in-flight 

SMS that we are aware of, with the exception of previous 

SMS experience (34,35), caution must be exercised. The 

preflight differences in nystagmus frequency and total 

amplitude were not statistically significant; therefore, any 

predictive capability may be fortuitous. In addition, the 

lack of a constant visual background during our studies, 

a factor that may alter the effectiveness of VOR 

suppression (7), may have introduced variability into the 

results. 

We have shown that space fight per se does not affect 

visual suppression of the VOR. In subjects who have SMS, 

suppression may not be as complete as in unaffected 

individuals. This difference between the two populations 

may serve as a potential indicator of preflight susceptibility 

to SMS, although the results in this study need to be 

repeated with standard visual backgrounds and a larger 

population. Further study of this phenomenon may shed 

light on the mechanism of SMS in particular and 

adaptation to the space flight environment in general. 

4 
Acknowledgements 

The authors gratefully acknowledge the assistance of the 

following individuals, among others: Gen. James 

Abrahamson for fiscal and administrative support, Mr. 

Aaron Cohen and Dr. William Shumate for making this 

publication possible, Messrs. Hugh Harrington and Phil 

Gainer for technical aid, Mr. Henry Whitmore for 

hardware design and fabrication, Dr. Howard Schneider 

and Mr. Sid Jones for publication assistance, Dr. Cecil 

Hallum for statistical evaluation, and especially the 

crewmembers who participated in this study. 

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5 
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6 
Appendix - Data Tables 

Table A1.- Preflight VOR suppression nystagmus data. 

Frequency Mean Total 

amplitude, amplitude, 

degrees degrees 

Frequency Mean Total 

amplitude, amplitude, 

degrees degrees 

Subject 1 Subject 11 

L-46 days 16.0 1 .o 16.0 

L-44 days 22.0 2. I 46.2 

L-37 days . 14.0 0.6 8.4 

L-33 days 9.0 0.8 7.2 

Subject 12 

L-28 days 22.0 3.6 79.2 

L-14 days 11.0 1.5 16.5 

Subject 2 

L-35 days 4.0 3.1 12.4 

L-14 days 13.0 5.6 72.8 

L-28 days 14.0 4.1 57.4 

L-182 days 12.0 1.3 15.6 

L-49 days 11.0 2.4 28.6 

L-43 days 16.0 2.6 41.6 

L-42 days 16.0 2.5 40.0 

L-35 days 14.0 1.5 21.0 

L-8 days 10.0 2. I 21.0 

Subject 13 

Subject 3 

~ ~~ 

L-70 days 4.0 2.2 8.8 

L-47 days 4.0 1.4 5.6 

Subject 4 

L-182 days 12.0 1.7 20.4 

L-42 days 8.0 3.4 27.2 

L-14 days 11.0 2.2 24.2 

L-8 days 8.0 2.2 17.6 

L-35 days 6.0 3.5 21.0 

L-69 days 8.0 5.0 40.0 

L-14 days 5.0 4.7 23.5 

Subject 5 

L-47 days 10.0 2.5 25.0 

Subject 14 . 

L-182 days 16.0 2.9 46.4 

L-51 days 13.0 2.2 28.6 

L-49 days 15.0 2.4 36.0 

L-8 days 20.0 2.1 42.0 

L-6 days 23.0 2.1 . 48.3 

Subject 6 

L-52 days 5.0 4.1 20.5 

L-47 days 5.0 3.3 16.5 

Subject 7 

L-39 days 4.0 2.1 8.4 

L-37 days 5.0 I .4 7.0 

~~~ ~~ 

Subject 15 

L- 182 days 7.0 3.7 25.9 

L-49 days 10.0 3.4 34.0 

L-42 days 12.0 7.8 93.6 

L-41 days 7.0 3.7 25.9 

L- I4 days 9.0 3.5 31.5 

L-7 days 9.0 2.6 23.4 

Subject 8 

L-46 days 11.0 1.8 19.8 

L39 days 3.0 1.4 4.2 

Subject 9 Subject 16 

L-39 days 10.0 1.6 16.0 

L32 days 14.0 2.3 32.2 

L- I82 days 

L-57 days 

L-40 days(#l) 

L-40 days(#2) 

L-35 days 

L-32 days 

L- 14 days 

L-8 days 

L-7 days 

16.0 

31.0 

26.0 

21.0 

15.0 

15.0 

17.0 

20.0 

16.0 

3.3 

2.4 

2.9 

4.2 

3.6 

3.5 

3.8 

2.9 

2.6 

52.8 

74.4 

75.4 

88.2 

54.0 

52.5 

64.6 

58.0 

41.6 

Subject 10 

~~~~~ 

L-46 days 8.0 1.4 11.2 
Table A2.- Frequency of nystagmus beats per two herd Table A3.- Mean amplitude of nystagmus beats, in 

oscillation cycles degrees 

In-flight Mission Day in-flight Mission Day 

~ ~~~~ ~ ~~ 

Subject Preflight 1 2 3 4 5 6 R+OD Subject Preflight 1 2 3 4 5 6 R+OD 

I 16.5 9.0 10.0 11.0 

2 10.3 3.2 

3 4.0 7.0 6.0 8.0 

4 6.5 2.0 13.0 

5 10.0 7.0 3.0 19.0 

6 5.0 5.0 6.0 6.0 

7 4.5 8.0 5.0 

8 7.0 3.0 5.0 

9 12.0 8.0 17.0 10.0 

10 8.0 16.0 

I1 15.3 13.0 8.0 15.0 13.0 13.0 19.0 

12 13.2 13.0 16.0 

13 9.0 0.0 7.0 8.0 

14 17.4 24.0 16.0 14.0 

15 9.0 0.0 0.0 7.0 

16 19.7 18.0 19.0 

I 2.6 2.0 1.7 I .4 

2 4.3 2.5 

3 1.8 2.6 1.7 I .7 

4 4.9 3.2 4. I 

5 2.5 3.4 3.5 1.3 

6 3.7 4.8 6. I 3.0 

7 I .8 4.4 4.5 

8 1.6 4.5 3.2 

9 2.0 1.6 2.9 3.3 

10 1.4 2.4 

11 1.1 1.5 2.9 1.6 1.8 2.0 1.8 

12 2.1 2.0 I .3 

13 2.6 0.0 1.1 1.3 

14 2.3 2.4 2.8 I .7 

15 4.1 0.0 0.0 2.2 

16 3.2 2.0 2.8 

Table A4.- Cumulative nystagmus amplitude, in degrees 

In-flight Mission Day 

Subject Preflight 1 2 3 4 5 6 R+OD 

1 42.9 18.0 17.0 15.4 

2 44.3 8.0 

3 7.2 18.2 10.2 13.6 

4 31.9 6.4 53.3 

5 25.0 23.8 10.5 24.7 

6 18.5 24.0 36.6 18.0 

7 8.1 35.2 22.5 

8 11.2 13.5 16.0 

9 24.0 12.8 49.3 33.0 

10 16.8 38.4 

11 16.8 19.5 23.2 24.0 23.4 26.0 34.2 

12 27.7 26.0 20.8 

13 23.4 0.0 7.7 10.4 

14 40.0 57.6 44.8 23.8 

I5 36.9 0.0 0.0 15.4 

16 63.0 36.0 53.2 

8 
1. Report No. 2. Government Accession No. 

TM 102 157 

4. Title and Subtitle 

Visual suppression of the vestibulo-ocular reflex during space flight 

6. Performing organization Code I 

3. Recipient's Catalog No. 

5. Report Date 

August I989 

7. Author(s) 

John J. Uri, William E. Thornton, Thomas P. Moore, Sam L. Pool 

9. Performing Organization Name and Address 

Lyndon B. Johnson Space Center 

Houston, Texas 77058 

2. Sponsoring Agency Name and Address 

National Aeronautics and Space Administration 

Washington, D.C. 20546 

8. Performing Organization Report No. 

S-598 

10. Work Unit No. 

073-36-00-00-72 

11. Contract or Grant No. 

13. Type of Report and Period Covered 

TM August 1989 

14. Sponsoring Agency Code 

Electro-oculography VOR suppression 

Space flight 

Space motion sickness 

Vestibulo-ocular reflex 

I 

5. Supplementary Notes 

John J. Uri, GE Government Services; William E. Thornton, Lyndon B. Johnson Space Center; Thomas P. Moore, 

Methodist Hospital of Indiana; Sam L. Pool, Lyndon B. Johnson Space Center. 

Unclassified - Unlimited 

Subject Category: 52 

6. Abstract 

Visual suppression of the vestibulo-ocular reflex was studied.in 16 subjects on four Space Shuttle missions. Eye movements 

were recorded by electro-oculography while subjects fucated a head-mounted target during active sinusoidal head oscillation 

at 0.3 Hz. Adequacy of suppression was evaluated by the number of nystagmus beats, the mean amplitude of each 

beat, and the cumulative amplitude of nystagmus during two head oscillation cycles. Vestibulo-ocular reflex suppression 

was unaffected by space flight. Subjects with space motion sickness during flight had significantly more nystagmus 

beats than unaffected individuals. These susceptible subjects also tended to have more nystagmus beats before flight. 

9. Security Classification (of this report) 20. Security Classification (of this page) 21. No. of pages 

Unclassified Unclassified 12 

7. Key Words (Suggested by Author(s)) 10. Distribution Statement 

22. Price 

For sale by the National Technical Information Service. Springfield, VA 22161-2171