b I 

ROLE OF ORIENTATION REFERENCE SELECTION 

IN MOTION SICKNESS 

Semiannual Status Report 

NAG 9-117, Supplement 2s 

Robert J. Peterka, Ph.D. 

and 

F. Owen Black, M.D. 

February 1987 

(hASA-CH-180151) RCZE CF CElEhl ASION N97- 174 3 1 

HjliEiiEidCE SELECYICH IN RC'IfCI IICKNESS 

Semiannual Status Beport (Gocd Sdmaritan 

Hcspital and) 10 F CSCL 06s Unclas 

G3/52 44015 

Neurological Sciences Institute and 

Department of Neuro-otology 

Good Samaritan Hospital and Medical Center 

Portland, OR 97210 
Summary of Proposa 1 

Previous experiments with moving platform posturography have shown that 

different people have varying abilities to resolve conflicts among vestibular, 

visual , and proprioceptive sensory signals. In particular, there is one class 

of subjects with a vestibular disorder known as benign paroxysmal positional 

vertigo (BPPV) who often are particularly sensitive to inaccurate visual 

information. That is, they will use visual sensory information for the control 

of their posture even when that visual information is inaccurate and is in 

conflict with accurate proprioceptive and vestibular sensory signals. BPPV has 

been associated with disorders of both posterior semicircular canal function 

and possibly otolith function. The conceptual basis of the present proposal 

hinges on the similarities between the space motion sickness problem and the 

sensory orientation reference selection problems associated with the BPPV 

syndrome. These similarities include both etiology related to abnormal 

vertical canal-otolith function, and motion sickness initiating events provoked 

by pitch and roll head movements. 

The objectives of this proposal were developed to further explore and quantify 

the orientation reference selection abilities of subjects and the relation, if 

any, between motion sickness and orientation reference selection. The overall 

objectives of this proposal are to determine (1) if motion sickness 

susceptibility is related to sensory orientation reference selection abilities 

of subjects, (2) if abnormal vertical canal-otolith function is the source of 

these abnormal posture control strategies and if it can be quantified by 

vestibular and oculomotor reflex measurements, and (3) if quantifiable measures 

of perception of vestibular and visual motion cues can be related to motion 

sickness susceptibility and to orientation reference selection ability 

demonstrated by tests which systematically control the sensory information 

a vai 1 ab1 e for ori enta ti on. 

Summary of Project Status 

Three test devices are required for the proposed experiments. They are (1) 

moving posture platform, (2) servo controlled vertical axis rotation chair with 

an independently controllable optokinetic stimulator, and (3) servo controlled, 

hydraulic powered two-axis rotation chair for the generation of pitch and roll 

motions. The first two devices are currently functional and are routinely used 

for both clinical and research testing. The third device is under development. 

The development of the this two-axis rotator has been a major focus in the 

first half of this project year and will be described in more detail below. 

The second major focus was to begin preliminary experiments using the 

perceptual feedback technique developed by Zacharias and Young (Exp Brain Res, 

41:159-171, 1981). This project required both hardware modification of 

electronics for our vertical axis rotation chair and development of software 

for the control of the experiment and data collection, and software for the 

analysis of the data. 

1 
Two-axis Rota tor Development 

The two-axis rotator has been under development for the past two years. Most 

of the funds for this development came from startup money associated with the 

PI'S move to Good Samaritan Hospital. Additional funds in the current NASA 

project are supporting the final phases of development. Figure 1 shows a line 

drawing of the rotator. It consists of two gimbals powered by rotary hydraulic 

actuators. The inner gimbal produces yaw axis rotations of the subject. The 

outer gimbal rotates the subject about a horizontal axis which passes through 

the subject's ears. Figures 2 shows photographs of the two-axis rotator taken 

on February 9, 1987 in a machine shop in Pittsburgh, PA where it was 

constructed. The device has since been shipped to us and we have begun its 

installation. We have been preparing for the arrival of the device by 

constructing the electronic circuits necessary for the hydraulic servo system. 

These circuits have been completed for the yaw axis drive, and are 90% 

completed for the pitch axis drive. The control circuits provide for both 

position and velocity servo control loops, and the ability to switch between 

the loops under computer control. The circuits include an adjustable 

compensation network which can fine tune the dynamic properties of the servo 

loops. Additional circuits have been completed for the buffering and scaling 

of position and velocity signals from the yaw and pitch actuators, and a safety 

shutdown circuit which shunts the hydraulic supply pressure and turns off the 

pump if either of the axes move out of range. Additionally there are fluidic 

shock absorbers to cushion the stop if the device were to go out of control. 

A preliminary stimulus control program has been written for the LSI 11/73 

computer which interfaces with the two-axis rotator. The program provides for 

turni ng on and off hydraulic power, swi tchi ng be tween posi ti on and vel oci ty 

servo loop modes, zeroing of drift in velocity mode, and delivering sinusoidal 

and square wave stimuli. This program is currently used for calibrating and 

adjusting servo loop compensa ti on networks. The program wi 11 later be expanded 

into a full data collection and stimulus control program. 

Pe r cep t ua 1 Feedback Ex per i men t s 

in 1981, Zacharias and Yoiing presented a method which allowed for the 

quantification of a subject's perception of rotation under the combined 

influence of visual and vestibular cues. In this technique, the subject has 

control over the rotational motion of the chair by adjusting a potentiometer. 

The subjects are seated in the vertical axis rotation test room with the 

potentiometer mounted on the arm of the chair. The output of this 

potentiometer is summed with the velocity command signal from a computer and 

this summed signal is delivered to the velocity command input of the chair's 

servo motor. A "perfect" subject would be able to hold themself stationary in 

space by adjusting the potentiometer so that its output was equal but opposite 

to the computer's command signal. "Real" subjects do not remain stationary 

because of the dynamics of the motion perception and motor reaction systems, 

and because of presumed imbalances in the vestibular receptors. 

The rotation of the subject's chair and the visual surround can be 

independently manipulated. We have used 6 different sensory environments for 

our preliminary experiments. These include (1) chair rotation in the dark, (2) 

rotation of the visual surround with the chair stationary, (3) chair rotation 

2 
with the visual surround velocity equal to the chair velocity, (4) chair 

rotation with a constant velocity surround, (5) chair rotation with the 

velocity of the visual surround equal to the chair velocity plus a constant, 

and (6) chair rotation with a stationary visual surround. Condition (2) is 

used to test the motor control dynamics of the subject. Conditions (1) and 

(3)-(6) represent a variety of sensory environments in which the subject is 

forced to deal with either accurate, inaccurate, conflicting, or absent sensory 

cues about their motion. 

The hardware has been modified in our vertical axis rotation test room to 

accommodate these perceptual feedback experiments. Additionally we have 

written a stimulus control and data collection program for these experiments. 

We can define either a sum-of-sines or pseudorandom stimulus or a single 

frequency sinusoidal stimulus which the subject must balance out under the 

various sensory environments. The program collects 6 channels of data at 100 

samples per second. These channels include chair velocity, optokinetic 

projector velocity, chair command velocity (from the computer), optokinetic 

projector command velocity, the subject's feedback potentiometer signal, and 

horizontal eye position recorded from an EOG amplifier. This data is stored in 

a disk file for later analysis. We have also written a preliminary data 

analysis program which at this point consists of simply printing out and 

labeling the six channels of data from the various test conditions. 

Results from three different subjects under condition (11, rotation in the 

dark, are shown in Figures 3-5. One of these subjects was able to remain 

nearly stationary throughout the test (Figure 3, top trace). The other two, 

shown in Figures 4 and 5, drifted slowly to the left. These results are 

similar to those obtained by Zacharias and Young, although they did not test 

their subjects in a dark environment. This drift was attributed to possible 

biases introduced by imbalances between the two ears. 

The goal of these preliminary experiments is to (1) gain experience with this 

technique, (2) verify the results of Zacharias and Young, (3) extend the 

results of Zacharias and Young by including additional sensory environments, 

and (4) determine the consistency of results for individual subjects tested 

over time. These techniques will later be extended to the two-axis rotator, 

compared with results of moving platform posturography, and correlated with the 

results of vestibular and oculomotor reflex measurements and measurements of 

motion sickness susceptibility. 

Addi ti ona 1 Nork 

We have purchased a small servo motor, controller, and power supply for use in 

an optokinetic stimulator for the two-axis rotation device. The design of this 

projector is nearly completed and parts for its construction have been ordered. 

This projector will be movable in order to allow both horizontal or vertical 

motions of the visual stimulus. 

Other efforts include the completion of the data analysis of the 200 normal 

subjects. Data from these subjects was collected as part of previous NASA 

projects (NCC9-8 and NAG 9-117). A paper based on this data was presented at 

the Association for Research in Otolaryngology meeting in February 1987. A 

copy of this abstract is attached at the end of this report. Two papers for 

publication are nearly completed, and will be submitted to Experimental Brain 

Research in the next month. 

3 
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Figure 5 
AGE RELATED CHANGES IN HUMAN VESTIBULOOCULAR AND YESTIBULOSPlNAL REFLEX 

FUNCTION. *R.J. Peterka, F.O. Black, C.D. Newell, and M.B. Schoenhoff.. 

Neurological Sciences Insti ts andpartment of Neuro-otology, Good 

Samartitan Hospital and Medical Center, Portland, Oregon 97210. 

The function of the vestibuloocular reflex (VOR) and vestibulospinal (VS) 

systems was tested in 216 normal human subjects aged 7 to 81 years. The 

distribution of ages was nearly uniform. All subjects met criteria which 

included normal age corrected auditory function, negative histories of 

dizziness or equilibrium problems, neurological problems, ototoxic drug use, or 

head blows of sufficient magnitude to cause loss of consciousness or skull 

'fracture. 

VOR tests were performed in the dark and included sinusoidal rotations 

about a vertical axis at 0.05, 0.2, and 0.8 Hz and a pseudorandom stimulus 

consisting of the sumnation of 8 sinusoidal components from 0.01 TO 1.5 Hz. 

Slow phase eye velocity responses were analyzed. to obtain VOR gain, phase, 

average value, and asymmetry. 

YS testing was performed with a subject standing on a platform and within 

a visual field enclosure. Both the platform and visual field could be 

independently rotated about the ankle joint axis. The anterior-posterior body 

sway of the subject was monitored by a potentiometer with a wand attached at 

the subject's hip. Each subject was asked to stand during six 20 second trials 

during which they were exposed to various combinations of eyes open, eyes 

closed, and platform and/or visual field rotations. Platform and visual field 

rotations were always in the direction of and in proportion to the subject's 

actual body sway. Rotations of this type limit the proprioceptive and visual 

sensory information available for the control of posture. 

Age related trends were observed in both VOR and VS function. There were 

significant VOR gain decreases at all test frequencies and phase increases at 

0.2 Hz and above with increasing age. There was a small but insignificant 

decrease in the VOR time constant with an associated small increase in low 

frequency phase leads. All trends in VOR response parameters were small with 

respect to the overall variability of the dat?. Decreasing VS function with 

increasing age was revealed by the increased number of falls on two or more of 

the six posture test trials. Subjects 60 and older accounted for 54% of these 

falls. The pattern of falls was. not random, but occurred mostly on two pairs 

of trials. One pair consisted of trials in which the visual field rotated in 

proportion to the subject's sway indicating that these subjects relied 

primarily on vision for the control of their balance. The other pair consisted 

of trials in which both proprioceptive and visual information were removed 

forcing the subject to use only vestibular cues. 

Subjects who fell two or more times during VS testing where more likely to 

have VOR response parameters on the fringes of the population distributions. 

This indicates that subjects who fell on two or more trials had vestibular 

function which was impaired with respect to the remainder of the population. 

Mi thin this selected normal population, one could reasonably conclude that 

about 10: of the population had significant functional vestibular deficits, and 

that most of these deficits occurred in older subjects. 

Subjects were not rejected based on vestibular test results. 

(Supported by NASA grants NCC 9-8 and NAG 9-117) 

Abstract of paper presented at Tenth Association for 

Research in Otolaryngology Meeting, February 1987