WO1988004909A2

WO1988004909A2 - Apparatus and method for determining the presence of vestibular pathology

Info

Publication number: WO1988004909A2
Application number: PCT/US1988/000007
Authority: WO
Inventors: Lewis M. Nashner
Original assignee: Neurocom International, Inc.
Priority date: 1987-01-06
Filing date: 1988-01-04
Publication date: 1988-07-14
Also published as: WO1988004909A3

Abstract

The apparatus consists of a support surface (11) on which the subject (10) stands erect. The surface (11) is rotatable around an axis (12) co-linear with the ankle joints and rests on vertical force transducers (13), the signals from which are monitored by the computer (14). The subject's field of view is substantially surrounded by an enclosure (15) which is also rotatable about the axis (12). The computer (14) controls the stimulator (18) of the inner ear vestibular system and monitors any resulting change in posture of the subject, moving the support as necessary. The computer then calculates whether or not the stimulus produces correlated and significant increases in one or more of the measured variables.

Description

APPARATUS AND METHOD FOR DETERMINING THE PRESENCE OF VESTIBULAR PATHOLOGY

DESCRIPTION

Technical Field

This invention relates generally to methods and devices for providing non-invasive, sensitive, and reliable tests for the presence of abnormalities in inner ear vestibular function. Such methods and devices are to be used as diagnostic tools for patients with symptoms of dysequilibrium, vertigo, and/or motion sickness.

Background Art

The inner ear vestibular system is composed of two laterally symmetric sets of end organs (see for example Chapters 3 and 4 in Wilson and Melvill Jones, 1979) . Each

SUBSTITUTE SHEET ear contains 5 spatially specific end organs for sensing head accelerations. In each ear three semicircular canals sense angular accelerations in three approximately orthoganal axes. The utricular otoliths sense the sum of gravity and linear head accelerations in a plane inclined approximately 30 degrees from horizontal.

Function of the saccule is less understood but is believed to include gravity and linear acceleration along an approximately vertical axis. Thus, individual vestibular end organs are involved in maintaining different components of posture and equilibrium. The horizontal canals are used primarily to control horizontal plane eye and head movements, while the vertical canals and otoliths help maintain front-back and side-to-side balance of the head and trunk. The spatial and functional specificity within the vestibular system provides an opportunity for selectively determining the extent of pathology of individual end organs by observing both head, eye, and body responses to vestibular stimulation. It is also known that the canal and otolith end organs sense different frequency components of linear and angular motion. Canals sense angular acceleration frequencies over the range of 0.1 to approximately 5 Hz, while the otoliths sense lower frequency linear accelerations in the range of 0 to 0.1 Hz (Meiry, 1966). Thus, the use of frequency selective signals is another possible means for isolating the function of individual vestibular end organs.

Vestibular pathology frequently affects only a portion of the vestibular end organs, sometimes in one ear and other times distributed either equally or unequally among the organs^"of the two ears (see for example Schuknecht, 1974) . While, the treatment of choice for the patient with vestibular pathology depends on the distribution and extent of involvement among the 10 end organs, the symptoms of the individual patient frequently do not reveal which organs are affected. Hence, objective methods for assessing the function^* of individual vestibular end organs are essential to the comprehensive vestibular examination.

SUBSTITUTE SHEET To test vestibular functions head acceleration, stimuli can be imposed with precise time course, amplitude, and spatial specificity. However, precise acceleration stimuli cannot be effectively used to test vestibular end organs individually, because the lateral symmetry of the two inner ears means that acceleration- in any one axis will always excite end organs in both ears. Hence, several alternative means for selective stimulation of end organs in a single ear have been developed using non-physiologic inputs: (1) Using so called "galvanic" vestibular stimulation, end organs of one ear can be electrically excited by passing small currents between two or more surface electrodes affixed to the mastoid bone of the ear or other locations on the head (see for example Nashner and Wolfson, 1974) . (2) The so called "caloric" stimulus excites the horizontal semicircular canal end organ of one ear by creating a thermally induced pressure gradient within the horizontal canal (see for example Dayal, et al, 1973) . (3) In some instances changes in air pressure between the external canal and middle ear spaces of one ear can excite one or more end organs in that ear (see for example Daspit, et al, 1980) .

Various attempts have been made to use the "galvanic" vestibular stimulus as a clinical diagnostic tool (for examples, Ishihara, 1918; Fischer, 1956; Pfaltz and Koike, 1968) . In this test the vestibular end organs are selectively stimulated by passing small electrical currents between electrodes placed in different configurations on the mastoid bones. Placing one electrode on each mastoid bone stimulates receptors in both inner ears in opposite directions, while two electrodes placed on a single mastoid bone stimulate receptors of one ear selectively. While the time course, amplitude, and frequency of electrical current stimuli can be precisely controlled, the distribution of stimulation among the 5 end organs of the stimulated ear can be accomplished only to a limited degree by altering the placement of the electrodes. Responses to electrical vestibular stimulation can be monitored as movements of the

SUBSTITUTE SHEET eyes (for example, Hozawa, 1961) or in the standing subject as body swaying (for example, Coats and Stoltz, 1969; Coats, 1973) .

Electrical stimulation of the vestibular receptor organs is a potentially useful clinical diagnostic method, because it can be used to quantify recfeptor function of one ear at a time and because the time course and frequency of stimulation can be precisely controlled. Electrical vestibular testing for this or any other purpose, however, is not currently a standard of practice in the clinic.

This is because relatively large currents are required to produce postural or eye movement responses when the subject is tested under passive seated or reclining positions. Large stimulus levels can cause the patient significant discomfort. Furthermore, the resulting eye movement and sway responses are small, making the repeatability reliability of the resulting measurements poor.

The use of "caloric" stimulation is already a standard practice in the currently used clinical vestibular examination, and several manufacturers produce caloric stimulation devices for this purpose. With the caloric test, the patient assumes a passive reclining position on a chair or bed. The head is positioned tilted 30 degrees back so that the plane of the horizontal canals is oriented roughly vertical. Then, hot or cold water is introduced to one ear and the amplitude and duration of nystagmoid eye movement responses observed subjectively or measured using electronystag ography (ENG's) . Alternatively, bilateral stimuli can be imposed by introducing thermal stimuli of either the same or opposite temperatures to the two ears simultaneously.

The caloric test is currently used by clinicians to identify asymmetries in function between the two ears. The sensitivity and specificity of this method is limited, however, for several reasons. First, with currently available methods, the thermal input stimulates only the horizontal canals and therefore does not detect asymmetries involving the vertical canals or otoliths. Second, the

SUBSTITUTE SHEET a plitude and frequency of the thermal stimulus cannot be controlled precisely, because heat conduction through the temporal bone is slow and varies among patients. Thus, the time course of the thermal vestibular stimulus is also slow and tests only the lowest frequency component of the horizontal canal response. Third, patients frequently become dizzy, motion sick, or nauseous with the caloric test.

The third method for selectively stimulating one or more vestibular end organs is to alter the pressure between the external and middle ear spaces. As with the caloric vestibular test, pressure stimuli are introduced with the patient in a passive seated or standing position. The foregoing references are identified in the list of references attached hereto and incorporated herein by reference as Exhibit A.

DISCLOSURE OF INVENTION

The present invention provides new methods and apparatus for significantly improving the specificity, accuracy, and reliability of non-invasive tests for the presence of inner-ear vestibular disorders. My invention does not propose novel ways for selectively stimulating inner ear vestibular end organs. Rather, it provides new methods and devices for placing the subject in tasks where an equilibrium position is actively controlled, stimulating the vestibular end organs, and then measuring the subject's displacements from the maintained equilibrium position in response to the stimulation.

In accordance with methods of the present invention, the subject performs an active posture control task by assuming a position in equilibrium on a movable support surface and within a second independently movable visual

SUBSTI enclosure. First, one or more quantities related to displacements of the subject's body from the assumed equilibrium position are measured. Second, either one or both of the support surface and visual enclosure are moved 5 in functional relation to one of the measured quantities. Moving the support surface and visual -enclosure in functional relation to the subject's displacements from equilibrium disrupts information about the subject's equilibrium position normally available from the visual and

1₀ somatosensory inputs. Under these altered sensory conditions, the subject must actively maintain equilibrium by increasing his reliance on vestibular orientation information.

I call conditions in which the support surface and

₁₅ visual enclosure are moved in functional relation to a quantitiy related to the subject's displacements from equilibrium "sway-referenced" support and visual conditions, respectively. The term sway-referenced is used, because the surfaces used as orientation references

2o by the somatosensory and visual systems move in relation to the subject's displacement from the assumed equilibrium position rather than remain fixed in relation to gravity. ---- If the subject relies on somatosensory or visual inputs during sway-referenced conditions, then he will have an

25 inaccurate perception of his position in equilibrium.

I call the axis about which the support surface and visual enclosure move during sway-referencing the "sway-reference axis". Information about the subject's position in equilibrium is disrupted only in the axis of

₃₀ body motion aligned with the sway-reference axis. The extent to which sway-referencing disrupts somatosensory and visual information about the subject's position in equilibrium in the sway-refernce axis can be modified. During sway-referenced conditions, the amplitude

₃5 of the support surface and visual enclosure motions can be equal to, a fraction of, or a multiple of the measured quantity related to the subject's displacement from equilibrium. When the support surface and visual enclosure

SUBSTITUTE SHEET move ents are equal to the measured quantity, then orientation information in the direction of displacement aligned to the sway reference axis is substantially disrupted. When support and enclosure movements are a fraction of the measured quantity of the subejet's displacement from equilibrium, the perception of displacement from a position in equilibrium will be reduced. I use the term sway-reference "gain" to mean the amplitude relation between the measured quantity of body ^■ displacement from equilibrium and the motion of the sway-referenced surface.

Depending on the overall medical status of the subject, the inner ear vestibular system can be stimulated while the subject assumes an active posture control task in various different positions in equilibrium. In one preferred embodiment, the subject assumes an erect standing position in equilibrium. According to methods already described in my previous patent application serial number 873,125, filed June 11, 1986, the support surface and visual enclosure are each sway-referenced to a measured quantity related to the antero-posterior displacements in the subject's center of body mass by rotating these surfaces about a common axis of rotation approximately co-linear with the ankle joint axis. In this embodiment, the sway-refernce axis is aligned with the antero-posterior axis of the subject's body sway. As described in further detail below, numerous other embodiments are possible.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 shows a schematic block diagram of the principal components of a possible embodiment of an apparatus according to the present invention.

Fig 2 shows a block diagram of the principle steps of a possible embodiment of a method according to the present invention.

Fig.3 shows the head and body of a standing subject positioned such that the end organs of the left superior and right inferior vertical canals are aligned with the support surface and visual enclosure sway-reference axes.

Fig. 4 illustrates the sequence of events measured during a typical vestibular responsiveness test conducted according to a possible embodiment of the present invention.

Fig. 5 illustrates a possible embodiment of means for controlling the rotational position of the support surface.

Fig. 6 illustrates a second simpler means for providing a support surface which rotates in functional relation to a quantity related to the subject's displacement from equilibrium.

Fig. 7 shows an arrangement for introducing a controlled thermal stimulus to one ear. Fig. 8 shows a preferred embodiment of a method according to the present invention.

Fig. 9 illustrates the sequence of events measured during an electrical test of the left superior and right inferior semicircular canal end organs conducted according to a preferred embodiment of the method shown in Fig. 8.

Fig. 10 shows simpler means for providing a support surface which rotates in functional relation to a quantity related to the subject's displacement from equilibrium.

DESCRIPTION OF SPECIFIC EMBODIMENTS

In co-pending application serial no. 873,125, filed June 11, 1986, for an invention by me, a method and apparatus were described which force a subject to use vestibular orientation information while maintaining a position in equilibrium. Somatosensory (inputs from contact with the support surface) and visual orientation inputs to the subject are made inaccurate and thereby disrupted for sensing position in equilibrium by: (l) placing the subject on a movable support surface and within a separately movable enclosure completely surrounding his field of view, (2) measuring one or more quantities related to the spontaneously occurring displacements of the subject away from the equilibrium position, and then (3) moving either one or both of the support surface and visual enclosure in functional relation to one of the measured quantities.

In two preferred embodiments of the previous Nashner invention, the support surface and the-visual enclosure are each independently rotatable about the εame axis. In one preferred embodiment, the subject stands erect with his ankle joints either co-linear with or perpendicular to the rotational axes of support surface and visual enclosure. In another preferred embodiment, the subject is seated on the support surface with the rotational axis of the hip joints either co-linear with or perpendicular to the rotational axes of the support surface and visual enclosure. According to a preferred protocol of the Nashner invention, the support surface, the visual enclosure, or both, rotate in direct functional relation to the rotational displacements of the subject's center of body mass in relation to the feet. These are called "sway-referenced" support surface and visual conditions, respectively. Under sway-referenced support surface conditions with eyes closed or sway-refernced support and visual surface conditions with eyes open, a subject who may be seated or standing on the platform support surface is forced to rely on vestibular inputs to maintain his position in equilibrium. Under these conditions, therefore, the patient is maximally dependent on vestibular stimuli to maintain the assumed equilibrium position.

In addition to the embodiment where the sway-reference axis is aligned with the antero-posterior axis of the subject's body sway, in a second embodiment, the subject can stand with the support surface and visual enclosure axes perpendicular to the ankle joint axis, and the support surface and visual enclosure sway-referenced to the side to side displacements in the subject's center of body mass.

In this embodiment, the sway-reference axis is aligned with the side to side direction of body sway.

In addition to the above described positions, the subject's head can be positioned to align the sensitive

SUBSTITUTE SHEET axis of one vestibular end organ of one ear with the sway-reference axis. When the subject is positioned with the ankle joints aligned to the sway-reference axis and the head turned 45 degrees to the left, for example, the sensitive axes of the inferior vertical canal end organ of the right ear and the superior vertical canal end organ of the left ear are each aligned with the sway-reference axis. With the head turned 45 degrees to the right, the sensitive axes of the superior vertical canal end organ of the right ear and the inferior vertical canal end organ of the left ear are now aligned with the sway-reference axis. With the subject positioned ankles perpendicular to the sway-reference axis and the head tilted back 60 degrees, the sensitive axes of the left and right ear horizontal canal end organs are aligned with the sway-reference axis of the support surface and visual enclosure.

If a stimulus is introduced to one ear with the sensitive axis of one vestibular end organ aligned with the sway-referenced axis, then the subject will be maximally dependent on orientation information from the end organ aligned to the sway-reference axis and therefore maximally sensitive to stimulation of the aligned vestibular end organ. Thus, by stimulating the vestibular system of one ear with the head and body re-positioned in relation to the sway-reference axis, each inner ear vestibular end organ can be selectively tested for sensitivity to stimulation.

If the condition of the subject does not allow testing in an erect standing position, then the subject can maintain an erect seated position in equilibrium and be tested using proceedures similar to those described above. In one embodiment of the erect seated position test, the axes of the support surface and visual enclosure are aligned co-linear with the-hip joints. With this alignment the support surface and visual enclosure are sway-referenced by rotating them in functional relation to the antero-posterior displacements of the subject's center of trunk mass from equilibrium. In this position the sway-reference axis is aligned with the antero-posterior direction of trunk sway.

SUBSTITUTE SHEET Alternatively, the hip joint axis can be aligned perpendicular to the rotational axis of the support surface and visual enclosure. With this alignment the surfaces are rotated in relation to the side-to-side displacements of the subject's center of trunk mass from equi.li.bri.um. In this position, the sway-reference axis is aligned with the side-to-side direction of trunk sway.

In the seated embodiment of the test, the subject's head can also be turned to one side or tilted backward to selectively align a single vestibular end organ of one ear with the sway-reference axis.

It can be appreciated that the embodiments of the present invention involve placing the subject in an active equilibrium control task, positioning the subject's body and head in relation to the sway-reference axes of the support surface and visual enclosure, and then sway-referencing the support surface and visual enclosure to selectively sensitize a single vestibular end organ to stimulation and are not limited to the erect standing or seated positions. For example, the rotational axis of the support surface and visual enclosure can be aligned with one of the three axes of head rotation at the neck joint. The support surface and visual enclosure can then be sway-referenced to the antero-posterior or side-to-side tilting of the head. And, the rotational axis of the visual enclosure can be aligned with an axis of eye rotation in the head and the enclosure sway-referenced to the rotational motions of the eyes.

My method for sway-referencing the support surface and visual enclosure can also be performed about several axes at the same time. Multiple axis sway-referencing requires a support surface and visual enclosure capable of rotation about a plurality of axes.

It can also be appreciated that the responsiveness of individual vestibular end organs to stimulation can be tested selectively while the subject maintains a position in equilibrium with the support surface and visual enclosure sway-referenced one at a time. Furthermore, vestibular end organ responsiveness to stimulation can be

SUBSTITUTE SHEET selectively determined by using sway-reference gains less or greater than unity. Gains less than unity are required for subjects who cannot maintain positions in equilibrium with sway-reference gains of unity. Gains greater than unity may be required for the subejct with exceptionally good balance control.

Depending on what aspect of inner-ear vestibular function is to be selectively tested under sway-referenced support surface and/or visual enclosure conditions, three different forms of controlled vestibular stimuli can be used:

(1) If the purpose of the test is to identify selective losses in vestibular function, vestibular end organs of one ear can be selectively stimulated using controlled electrical currents. Electrically stimulating the vestibular end organs of one ear while a subject maintains a position in equilibrium with the sway-reference axes of the support surface and visual enclosure aligned with the sensitive axis of a single end organ of the ear is a new clinical method for detecting vestibular abnormalities in the stimulated ear. By selectively increasing the responsiveness of the posture control system to stimulation of the aligned vestibular end organ, stimulus intensities are reduced (reducing pain and discomfort) and the sensitivity and reliability of measurements increased. Furthermore, ^"by aligning the sway-reference axis with the sensitive axis of a single vestibular end organ, the responsiveness of each end organ can be tested selectively. (2) A second means to stimulate the vestibular end organs of one ear while the subject maintains a position in equilibrium under sway-referenced conditions is to introduce controlled thermal stimuli to the external ear canal. In this new version of the caloric test, the sensitivity and reliability of the resulting measurements of vestibular function are improved by stimulating the vestibular system and measuring the subject's resulting displacements from equilibrium while the subject's posture control system is maximally sensitive to the vestibular

SUBSTITUTE SHEET sti ulus. As with the electrical stimulus method, the sway-reference axis of the visual enclosure and support surface can be aligned with the sensitive axis of a given vestibular end organ to selectively test the responsiveness of individual organs.

(3) The vestibular receptors can also be stimulated by introducing controlled changes in air pressure to the external canal of one ear. If the subject has one or more abnormal connections between the perilymph fluid and the inner ear space (perilymph fistula) , then one or more vestibular end organs will be stimulated by the pressure change. In the application filed as serial number 895,783 for an invention in which I was a co-inventor, a method was described for increasing the sensitivity and reliability of measurements of the subject's abnormal responsiveness of ear pressure stimulation. The present invention provides additional new methods for identifying on a selective basis which vestibular end organ or organs are abnormally responsive to pressure stimulation by aligning the sensitive axis of a vestibular end organ with the sway-reference axes of the support surface and visual enclosure. Furthermore, the present invention provides methods for performing the pressure test with the subject in seated and other positions in equilibrium. The equilibrium position of the body and displacements of the body from equilibrium can be measured by one or a combination of means, all well known in the prior art:

(1) The contractile activity of muscles generating the internal body forces for maintaining the equilibrium position can be measured using electromyographic (EMG) recordings. If the subject is maintaining an erect standing position in equilibrium, then ankle joint EMGs such as gastrocnemius and tibialis anterior can be recorded. If the subject maintains an erect seated position, then lower trunk EMGs such as paraspinals and abdominals are recorded.

(2) The support surface reaction forces maintaining the subject's equilibrium position can be recorded using a forceplate. Forceplates suitable for this purpose are

SUBSTITUTE SHEET anufactured by several companies (Kistler Corporation, 75 John Glen Drive, A herst, New York, 14120; Advanced Mechanical Technology, Inc., 141 California Street, Newton, Massachusetts, 02158; and NeuroCom International, Inc., 2326 N.W. Lovejoy Street, Portland, Oregon 97210) . The antero-posterior and side-to-side positions of the center of vertical force are particularly useful forceplate measures, because they can be used to calculate the approximate antero-posterior and lateral angular orientation of the center of body mass in relation to the ankle joints.

(3) Several means are available to measure directly the position of the body. Displacement transducers can be attached directly to the body. Alternatively, body positions can be measured by several commercially available computerized optical systems (Northern Digital Ltd. , 415 Phillip Street, Waterloo, Ontario, Canada N2L 3XQ) .

In a preferred embodiment of the present invention, the subject is placed on a movable support surface, and the subject assumes an erect standing position in equilibrium.

The subject's field of view is substantially surrounded with the visual enclosure, which is independently movable. The ankle joints are aligned with the sway-reference axis of the support surface and the visual enclosure. The subject's head is positioned 45 degrees to the left or right or tilted 60 degrees back to align the sensitive axis of one vestibular end organ with the sway-reference axis. The subject's displacements from equilibrium in the antero-posterior direction are measured on a continuous basis, and the support surface, the visual enclosure, or both are moved in functional relation to the measured displacements of the subject. Transient electrical, pressure, or thermal stimuli are introduced to one ear at a time. Then, the time course of the subject's displacements from the assumed equilibrium position^" in the absense of vestibular stimulation is compared to that during stimulation using statisitcal methods well known in the prior art. The extent of statistically significant changes in equilibrium position correlated with vestibular

SUBSTITUTE SHEET stimulation is a measure of the responsiveness of the aligned canal end organ to the imposed stimulation.

In a εecond preferred embodiment, the subject is placed on a movable support surface and assumes an erect seated position in equilibrium. The subject's field of view is subεtantially εurrounded with the visual enclosure, which is also independently movable. The hip joints are aligned with the support surface and visual enclosure εway-reference axes. The subject'ε head iε positioned 45 degrees to the left or right or tilted 60 degrees back to align the sensitive axis of one canal end organ with the sway-reference axis. Displacements of the subject's trunk from equilibrium in the antero-posterior direction are measured on a continuous basiε, and the εupport surface, the visual enclosure, or both are moved in functional relation to the measured displacements of the subject. Transient electrical, pressure, or thermal stimuli are introduced to one ear at a time. Then, the time course of the subject's displacements from the assumed equilibrium position in the absense of vestibular stimulation is compared to that during stimulation using statiεitcal methodε well known in the prior art. The extent of εtatiεtically εignificant changes in equilibrium position correlated with vestibular stimulation is a measure of the responsiveness of the aligned canal end organ to the imposed stimulation.

In a further specific embodiment based on the above embodiment, the subject εtands on a support surface, and the support surface and visual enclosure are each independently rotatable about a common axis co-linear with the subjects ankle joints. The support surface rests on three or more vertical force transducers. A digital computer samples signals from the force transducers and calculates the position of the center of vertical force exerted by the subject's feet onto the surface and the antero-posterior angular position of the subject's body center of masε in relation to the ankle jointε. The computer controls on a continuous basis the rotational positions of the support surface and visual enclosure, such

SUBSTITUTE SHEET that one or both of these surfaces rotate in functional relation to the calculated position of the center of vertical pressure or angular orientation of the subject's center of body maεs. The computer stores on a continuous basis the resultε of calculationε of the center of vertical force position and the angular position of the body center of mass in relation to the ankle joints. The computer initiates and controls stimuli to the vestibular system of one ear. Depending on the statiεtical ethodε used to calculate the significance of body displacements correlated with the vestibular stimuli, brief pulses of stimulation or continuously varying vestibular stimuli can be used. The computer then performs additional calculations using methods well known in the prior art to determine the statiεtical εignificance and extent of displacements from the equilibrium position correlated with the transient vestibular stimuli.

The following three versions of vestibular stimulation are used to determine different aspects of vestibular function:

(1) Pressure stimuli are used to identify abnormal connections between the middle and inner ear space. Pressure stimuli are introduced by inserting a tympanometer probe into the external canal and coupling the other end of the tube to a pressure generating device. The pressure generating device is controlled on a continuous basiε by the computer.

(2) Electrical stimuli can be introduced to the vestibular system in several different configurations. Placing one surf ce electrode on each of^" the two mastoid bones an passing a controlled current between the electrodes stimulates end organs in both ears. Placing two adjacent electrodes on a single mastoid bone selectively stimulates end organs of that ear. Electrical current between the two electrodes can be controlled on a continuous basis using a current generating device -operating under the control of the computer.

SUBSTITUTE SHEET (3) The vestibular end organs of one ear are thermally stimulated by introducing temperature controlled water or air to the external canal of the ear. The device for irrigating the ear with temperature controlled water or air can alεo be under the control of the computer.

It should be appreciated that other embodimentε of the preεent invention can alεo be used to teεt the εubject'ε postural reactionε to controlled changes in air pressure, eletrical current, or thermal stimuli while the subject is maximally sensitive to the resulting veεtibular inputs. By placing the subject with eyes closed in a position in equilibrium on a movable support surface and then moving the support surface in functional relation to the displacementε of the εubject from the equilibrium position, the movable visual enclosure can be eliminated. Now, the subject's posture control syεtem is maximally sensitive to vestibular inputs, because the εubject iε deprived of vision while somatosensory information derived from contact with the support surface is inaccurate. In a further simplification of this embodiment,^' the subject maintains a position in equilibrium on a passively complient rather than actively movable support surface. For example, if the subject maintains a standing position in equilibrium on a support surface with a purely elastic compliance about a rotational axis co-linear with the ankle joints, then the rotational orientation of the support εurface is εubstanially related to the antero-poεterior diεplacements in the position of the center of vertical force exerted by the subject's feet on the support εurface. If a combination of elastic and viscous complient elements is used in this embodiment, then rotations of the εupport surface will lag in time behind those of the center of vertical force. The correct combination of elastic and viscous forces, however, will result in a support surface displacement which is substantially in relation to the angular displacements of the subject'ε center of body mass.

SUBSTITUTE SHEET It should also be appreciated that the visual enclosure can alεo be moved in functional relation to the εubjectε diεplacements from the equilibrium position without an active controlling element. Specifically, a light-weight visual enclosure can be attached to a support surface compliant about a rotational axis co-linear with the ankle joints. In this embodiment, both the support surface and visual enclosure will rotate together. Fig. 1 εhowε a schematic block diagram of the principal componentε of an embodiment of an apparatuε according to the preεent invention. In this embodiment, the εubject 10 εtandε erect in a poεition of equilibrium on a support surface 11, which is rotatable about an axis 12 co-linear with the ankle jointε. The εupport surface rests on vertical force transducerε 13, the εignals from which are transmitted to the computer 14 for calculating angular displacementε of the subject's center of body masε from the equilibrium position. The subject'ε field of view iε εubεtantially εurrounded by an encloεure 15 which iε alεo rotatable about an axis co-linear with the ankle joints 12. The computer generates εignalε which, by way of position actuators, rotate the support surface 16 and visual enclosure 17 in functional relation to the computed angular displacement of the εubject'ε center of body mass. Then, the computer, by way of an actuator for stimulating the inner ear vestibular syεtem 18, initiateε and controls a stimuluε to one of the εubject'ε earε and then computes whether or not the stimuluε produceε correlated and εignificant increases in one or more of the measured variables of postural activity.

Fig. 2 shows one means for controlling the rotational position 20 of the support surface 11 about a rotational axis 12 approximately the height of the ankle joints above the surface, using a εyεtem compriεing an electric motor 21, lead εcrew 22, and a ball nut 23. Rotations of the motor and lead screw move the ball nut back and forth 24 and thereby rotate the support εurface 20. It can be appreciated that a similar εyεtem conεiεting of electric

SUBSTITUTE SHEET motor, lead screw, and recirculating ball nut can be used to rotate the visual enclosure. Alternatively, the rotational positionε of the support εurface and visual enclosure can be controlled by a syεtem consisting of an electric motor, fixed displacement hydraulic pump, and hydraulic cylinder.

Figure 3 showε a preferred embodiment for poεitioning the subject's feet 30, body 31, and head 32 to align the sway-reference axis with the senεitive axeε of the left εuperior 34 and right inferior 35 εemicircular canal end organε. In the εtanding embodiment of the teεt, the εubject stands on the rotatable support surface 11 with the ankle joint axis 33 co-linear to the common support surface and visual enclosure rotation axis 12 and with the head 32 turned 45 degrees to the left. In the seated embodiment of the test (not shown) , the εubject εits on the rotatable support surface and within the rotatable visual enclosure with the hip joint axis co-linear to the common support surface and visual enclosure rotation axis and with the head turned 45 degrees to the left. To determine the reεponεiveneεε of the left superior vertical canal receptor organ, controlled vestibular stimuli are introduced to the left ear. To determine the responsiveneεε of the right inferior canal end organ, the right ear iε εtimulated. The εensitive axes of the left inferior 41 and right superior 42 semicircular canal end organε are aligned with the εway-reference axiε aε εhown in Figure 4. In the εtanding embodiment of the teεt, the εubject εtandε on the rotatable εupport surface 11 and within the rotatable visual enclosure with the ankle joint axis 33 co-linear to the common support surface and visual enclosure rotation axis 12 and with the head 32 turned 45 degrees to the right. In the εeated embodiment (not εhown) , the εubject sits on the rotatable support surface and within the rotatable visual encloεure with the hip joint axis co-linear to the common support surface and visual enclosure rotation axis and with the head turned 45 degrees

SUBSTITUTE SHEET to the right. To determine the reεponεiveneεs of the left inferior vertical canal receptor organ, controlled vestibular stimuli are introduced to the left ear. To determine the responεiveneεε of the right εuperior canal end organ, the right ear iε stimulated.

The sensitive axes of the left 51^"and right 52 horizontal semicircular canal end organs are aligned with the sway-reference axis as εhown in Figure 5. In the standing embodiment of the test, the subject εtandε on the rotatable support εurface 11 and within the rotatable visual enclosure with the ankle joint axis 53 perpendicular to the common support surface and visual enclosure rotation axis 12 and with the head 32 tilted back 60 degrees. The seated embodiment is substantially similar to the standing embodiment, but the subject is positioned on the rotatable support surface and within the rotatable visual encloεure with the hip joint axiε perpendicular to the common εupport surface and visual enclosure rotation axis and with the head tilted back 60 degrees. To determine the responsiveness of the left horizontal canal receptor organ, controlled vestibular stimuli are introduced to the left ear. To determine the responεiveneεε of the right horizontal end organ, the right ear iε stimulated.

Fig. 6 shows an arrangement for introducing a controlled electrical stimulus to one ear. A pair of small εurface electrodeε 60 and 61 are placed next to one another over the mastoid bone of the ear to be stimulated. A current generator 63 is connected by wires to the two electrodes. The generator paεεeε low levels of current between the two electrodes.

Figure 7 showε an arrangement for introducing a controlled thermal εtimuluε to one ear. A small tube 71 is placed in the external ear canal 72. The other end of the tube is connected to a source of constant temperature water 73. Water is then pumped through the tube to irrigate the ear.

Figure 8 shows a perferred embodiment of a method according to the present invention. In this embodiment, a

SUBSTITUTE SHEET feedback loop 80-84 iε creating by poεitioning the subject on the support εurface and within the visual enclosure with the body and head aligned in relation to the sway-reference axis of the support surface and visual enclosure, having the subject εeek to maintain equilibrium 84, eaεuring the poεition of the vertical force center on the forceplate 80, calculating the diεplace ent angle of the body center of mass from equilibrium 81, multiplying the diεplacement angle by a gain factor to compute the diεplacing angle of the εupport εurface and viεual encloεure 82, moving the εupport εurface and/or viεual encloεure by the computed displacing angle 83, stimulating the εubject'ε veεtibular εystem according to a desired protocol 85, storing the measureε of vertical force center and body diεplacement angle on a continuouε baεiε 86, pulεe trigger averaging the force center and displacement angle measures with the vestibular stimuli 87, and then determining the extent to which the vestibular stimuli caused significant changes in the vertical force position and angular position eaεureε 88. Alternatively, the body diεplacement angle can be measured directly 81' rather than calculated from the forceplate measurementε.

Fig. 9 illuεtrateε the εequence of eventε meaεured during an electrical teεt of the left εuperior and right inferior εemicircular canal end organε conducted according to a preferred embodiment of a method εhown in Figure 8. Surface electrodeε are placed over the aεtoid bone of the left and then the right ear aε shown in Figure 6. The subject is poεitioned in relation to the εupport εurface and viεual encloεure εway-reference axiε such that sensitive axes of the left superior and right inferior semicirular canal receptor organs are aligned aε shown in Figure 3. The sway-reference gains for the visual enclosure and support εurface are εet and the viεual encloεure and εupport εurface are εway-referenced. Four meaεureε of the εubject'ε diεplacementε from equilibrium, two ankle muscle EMG's 91 and 92, the antero-posterior

SUBSTITUTE SHEET position of the center of vertical force 93, and antero-posterior angular orientation of the body center of mass in relation to the ankles 94, are recorded by the computer on a continuous basiε. Brief pulεeε of electrical current 90 are paεsed on a periodic basiε between the two mastoid bone εurface electrodeε, while-recording of the three meaεureε of postural activity continueε. Then, each of the three measures is enεe ble averaged in segmentε 95 time-locked to the onεet of the current pulεes. Significant changes in any of the three ensemble averaged measures are identified on a continuous basiε by εtatiεtical teεtε well known in the prior art.

In part A of Fig. 9, the εupport surface and visual enclosure are fixed (sway-referenced gains of zero) . The antero-posterior position of the vertical force center 93 and the angular displacement of the subject's center of body gravity with respect to the feet 94 move randomly as the subject εtandε erect. EMG traces from two ankle muscles 91 and 92 typically show little activity under this quiescent condition. After the subject has stood for a period of time, a series of brief current pulses 90 are introduced to the (normal) left ear. Ensemble averages of the four measures 96 - 99 show significant increases in the subject's displacement from equilibrium correlated with the current stimuli 90. Thiε reεult indicateε that the left superior canal end organ iε normally εensitive to electrical stimulation. No further electrical testing of the left superior end organ is therefore required.

In part B, the subject maintains the εame position as described.in part A, and the rotational position of the support surface and visual enclosure are again fixed (ie sway-reference gains of zero) . Now, after a period of quiescent standing, the current stimulus 90' is introduced to the (abnormal) right ear. With the surface fixed no significant postural reactions are obεervable in the e εemble averages of any of the measurementε 96*, 97', 98', and 99'. This result indicates that the senεitivity of

SUBSTITUTE SHEET the right inferior canal end organ to external electrical εtimulation iε reduced and that thiε organ iε therefore impaired.

In part C, further teεting of the right inferior canal is conducted to determine the extent of right inferior canal impairment. The εubject'ε head remains turned to the left. The the rotational orientation of the support surface and visual enclosure are now sway-referenced with gains of 1/4. After a period of quiescent standing, the current stimulus 90*' is again introduced to the (abnormal) right ear. With the surface sway-referenced at a gain of 1/4, εignificant poεtural reactionε are now obεervable in the emεemble average meaεurementε 96• ' , 97' ' , 98 ' ' , and 99' '. This result indiciates that the εenεitivity of the right εuperior canal end organ to external electrical εtimulation is only partially impaired.

Table I εummarizeε how εy metrical and asymmetrical losεeε in veεtibular function can be categorized according to the above deεcribed veεtibular function tests:

SUBSTITUTE SHEET -24-

Category Poεtural Reaction to Stimulation Ear A Ear B

I. Bilateral No reactionε No reactions Total Loεs at any sway- at any sway- reference gain reference gain or head position or head position

II. Bilateral Reactions at Reactions at

Partial Loss sway-referenced sway-referenced gains > 1/4 only gains > 1/4 only in all head in all head positions positionε

III. Bilateral Reactions in some Reactions in some Selective head positions head positions Losses with sway- with sway- reference gains = reference gains = 0, in others with 0, in others with gainε >_ 1/4 only gains __ 1/4 only

IV. Unilateral No reactions at Reactions with Total Losε any εway- fixed support reference gain and enclosure or head position V. Unilateral Reactions at Reactions with

Partial Loss sway-referenced fixed support gainε >_.1/4 only and enclosure in all head poεitionε

VI. Unilateral Reactionε in εome Reactions with Selective head positions fixed support Losε with sway- and enclosure reference gains = 0, in others with gains 1/4 only

VII. Normal Reactions with Reactionε with fixed support fixed εupport and enclosure and encloεure

TABLE I - Veεtibular Functional Losε Teεt

SUBSTITUTE SHEET A εubject iε placed in category I (bilateral total loεε) who εhows no significant postural reactions to brief stimulation of either ear with all combinationε of sway reference gains and head positionε in relation to the εway-reference axiε. A subject who has reactions to brief stimulation of either ear in all head positionε and with εway-referenced gainε of 1/4 or greater only iε placed in category II (bilateral partial loεs) . A subject who reacts to brief stimulation of either ear at sway-reference gains of zero with the head in some positionε in relation to the εway-reference axiε and at εway-reference gainε of 1/4 or greater in other head positions is placed in category III (bilateral selective losεeε) . A εubject who doeε not react to εtimulation of one ear under any and all combinations of sway-reference gain and head position in relation to the sway-reference axis, but who reacts to stimulation of the other ear with the support surface and visual enclosure fixed iε placed in category IV (unilateral total loεε) . A subj ct is placed in category V (unilateral partial losε) who reactε to electrical stimulation of one ear with the support surface and visual enclosure fixed and in the other ear only with sway-referenced gains of 1/4 or greater. A subject who reacts to brief stimulation of one ear at sway-reference gains of zero with the head in some positions in relation to the sway-reference axis and at sway-reference gainε of 1/4 or greater in other head poεitions, and who reacts to stimulation of the other ear with the support εurface and visual enclosure fixed is placed in category VI (unilateral selective loεε) . All remaining εubjects are placed in category N (normal) .

In all examples of the vestibular functional loss test, electrical or thermal stimuli can be used. In all including the perilymph fistula and vestibular functional loss tests, a support surface in which motions are actively controlled by a motor can be replaced with a εupport εurface with viεcoelaεtic compliant propertieε which moves paεεively in relation to the displacements of the subject from the maintained equilibrium position.

SUBSTITUTE SHEET Fig. 10 showε εuch simpler means for providing a εupport surface which rotateε in functional relation to a quantity related to the subject's displace from equilibrium. The support surface 11 is made compliant about the axis of rotation 12 by restraining the rotational motion of the εurface with a compliant"element 101. The compliant element can have purely elastic properties, εuch aε a linear spring, or it can have a combination of elaεtic and viscous properties, such as with a spring and fluid damper. Forces exerted by the subject against the support surface move the complient element 102 and thereby rotate the support surface 20. It should also be appreciated that the visual encloεure can be connected to the compliant εupport surface, such that both^* of these componentε will move in functional relation to the εubject.

In addition, variableε for determining the subject's postural activity other than those described in the preferred embodiments can be used. For example, the front-back or side to side changes in orientation of the center of body aεε can be measured with a potentiometer linked to the body with a belt and flexible coupling. Postural activity can also be measured by recording the electromyographic activity of one or more muscles providing postural εupport, uεing surface electrodes and high gain differential amplification.

SUBSTITUTE SHEET REFERENCES

1. Wilson, V.J., Melvill Jones, G. Mammalian Vestibular

Physiology. Plenum Press, New York, 365pp (1979)

2. Dayal, V.S., Farkaεhidy, J. , Kuzin, ^"B. Clinical evaluation of the hot caloric teεt aε a εcreening procedure, Laryngoscope 83: 1433 (1973)

3. Nashner, L.M. , Wolfson, P. Influence of head position and proprioceptive cues on short latency postural reflexes evoked by galvanic stimulation of the human labyrinth. Brain Research 67: 255-268 (1974)

4. Daspit, C.P., Churchill, D. , Linthicum, F.H. Diagnosis of perilymph fistula using ENG and impedance Laryngoscope 90: 217-223 (1980)

5. Iεhihara, A. Galvanic stimulation of the labyrinth. Jap, J- Otol. Tokyo 24: 482 (1918)

6. Fischer, J.J. Galvanic reaction. The Labyrinth. Grune and Stratton Inc. New York (1956)

7. Pfaltz, C.R. , Koike, Y. Galvanic test in central vestibular lesionε. Acta. Otolaryng. (Stockh) 65: 161 (1968)

8. Hozawa, J. A clinical conεideration on the nature of electrically εtimulated nyεtagmuε. Otologica Tokyo 33: 939 (1961)

9. Coats, A.C., Stoltz, M.S. The recorded body sway responεe to galvanic stimulation of the labyrinth , Laryngoscope 79: 85 (1969)

SUBSTITUTE SHEET 10. Coatε, A.C. Effectε of varying εtimulus parameters on the galvanic body sway response. Ann. Otol. 82: 96 (1973)

11. Meiry, J.L. The veεtibular εyεtem and human dynamic space orientation. NASA CR-628 (1966)

12. Schuknecht, H.F. Pathology of the Ear. Harvard University Press, Cambridge, (1974)

Claims

What is claimed is:

1. An apparatus for determining the presence of veεtibular pathology co priεing:

(a) a movable εupport surface on which a subject may assume an equilibrium position;

(b) measuring meanε for eaεuring a quantity related to the εubject'ε diεplacement from equilibrium;

(c) moving meanε, in connection with the meaεuring means, for moving the εupport surface in functional relation to the measured quantity, the value of the function exhibiting some dependency on the value of the εubject'ε diεplacement from equilibrium, so that the support surface is moved by the moving meanε in reεponεe to diεplacement of the εubject from equilibrium; (d) εtimuluε generating meanε for providing a controlled εti ulus to the subject'ε veεtibular εyεtem;

(e) program meanε, in communication with the moving means and the stimuluε generating meanε, for activating the moving meanε and the εtimuluε generating meanε in accordance with a diagnoεtic protocol;

(f) program meanε for recording the εubject'ε displacement from equilibrium and computing whether there is a significant change in diεplacement from equilibrium correlated with the controlled veεtibular εtimuluε.

2. An apparatuε according to claim 1, wherein the εtimuluε generating meanε includeε means for providing an electrical εtimuluε to the subject's vestibular syεtem.

3. An apparatuε according to claim 1, wherein the εtimuluε generating means includes means for generating a thermal stimuluε to the εubject'ε veεtibular εyεtem.

4. An apparatuε according to claim 1, wherein the εtimuluε generating meanε includeε meanε for generating a preεsure εtimuluε to the εubject'ε veεtibular εyεtem.

5. An apparatuε according to claim 1, further compriεing: viεual encloεure meanε for εubεtantially εurrounding the εubject'ε field of view;

SUBSTITUTE SHEET encloεure moving meanε, in connection with the meaεuring means, for moving the visual enclosure means in functional relation to the measured quantity, the value of the function exhibiting some dependency on the value of the subject's displacement from equilibrium, so that the visual enclosure means is moved by the enclosure moving means in response to displacement of the subject from equilibrium.

6. An apparatus according to claim 5, wherein the stimuluε generating means includeε meanε for generating an

10 electrical εtimulus to the subject's vestibular syεte .

7. An apparatuε according to claim 5, wherein the stimulus generating means includes means for generating a thermal stimulus to the subject'ε veεtibular εystem.

8. An apparatus according to claim 5, wherein the 15. stimulus generating means includeε meanε for generating a pressure stimuluε to the subject's vestibular system.

9. A method for determining on a selective basiε the responεiveneεs of individual inner ear vestibular end organs to an external stimulus in a subject placed in a

2₀ position of equilibrium and maintaining thiε poεition while somatosensory orientation information derived from the contact forces and motions of the feet and legs in relation to the support surface (hereinafter termed support surface inputs) are disrupted, such method compriεing:

25 A. placing the εubject on a movable εupport εurface and having the εubject aεεume a position in equilibrium thereon;

B. positioning the subject in relation to the axis of motion of the movable support surface (hereinafter termed

30 the "sway-reference axis") such that the sensitive axes of one or more vestibular end organε are εelectively aligned with the sway-reference axis;

C. measuring one or more quantitieε related to the εubject'ε diεplacement from the equilibrium poεition;

35 D. moving the εupport εurface in functional relation to one of the meaεured quantitieε;

SUBSTITUTE SHEET E. introducing to one ear or both earε εimultaneously a controlled external vestibular stimuluε;

F. determining whether or not the controlled external εtimuluε produceε εignificant correlated changeε in one or more of the meaεured quantitieε.

G. repeating proceedureε E and F-with the εubject in different positions in relation to the sway-reference axis; and

H. comparing the extent of correlated changeε to controlled external veεtibular εtimuluε with the εubject in different poεitionε in relation to the εway-reference axis.

10. A method, according to claim 9, for selectively determining the responεiveneεε of individual vestibular end organ receptors to an external stimulus while both support surface inputε and viεual orientation information derived from the otionε of the head and eyeε in relation to the visual surrounds (hereinafter termed visual inputs) are diεrupted, wherein εtep A includeε the additional εtep of εubεtantially εurrounding the εubject'ε field of view with a second movable surface (hereinafter termed visual encloεure) and step C includes the additional step of moving the visual enclosure in functional relation to one of the measured quantities.

11. A method, according to claim 9, for selectively determining the responεiveneεε of individual veεtibular end organ receptors to an external stimuluε in a εubject with εupport εurface inputε diεrupted and deprived of viεual inputε, wherein εtep A includeε the additional εtep of having the εubject cloεe his eyes.

12. A method for determining in a subject placed in a poεition of equilibrium and maintaining thiε poεition while visual inputs are disrupted has an abnormal connection between the middle and inner ear εpace, εuch method comprising: A. placing the subject on a support εurface and having the εubject assume a position in equilibrium;

SUBSTITUTE SHEET B. substantially εurrounding the subject's field of view with a movable viεual enclosure;

C. measuring one or more quantities related to the subject'ε displacement from the equilibrium position; D. moving the visual enclosure in functional relation to one of the measured quantities;

E. introducing to the external canal of one ear a controlled change in air pressure;

F. determining whether the controlled change in presεure causes significant change in one or more of the measured quantities.

13. A method for determining in a subject placed in a position of equilibrium and maintaining this position while both support surface and visual inputs are disrupted has an abnormal connection between the middle and inner ear space, εuch method compriεing:

A. placing the εubject on a movable εupport εurface and having the εubject aεεume a position in equilibrium;

B. subεtantially surrounding the subject's field of view with a movable visual enclosure;

C. measuring one or more quantities related to the subject's displacement from the equilibrium position;

D. moving the support surface and visual enclosure in functional relation to one of the measured quantities; E. introducing to the external canal of one ear a controlled change in air presεure;

F. determining whether the controlled change in preεεure causes significant change in one or more of the measured quantities.

14. A method for determining whether a εubject maintaining a poεition in equilibrium while support surface inputs are disrupted has an abnormal connection between the middle and inner ear space εelectively affecting the veεtibular end organε, εuch method compriεing: A. placing a εubject on a movable support surface and having the subject assume a position in equilibrium;

SUBSTITUTE SHEET B. positioning the subject'ε head εuch that the senεitive axiε of one veεtibular end organ of the ear iε aligned with the εway-reference axiε;

C. meaεuring one or more quantitieε related to the εubject's displacement from the equilibrium position;

D. moving the support surface in" functional relation to one of the measured quantities;

E. introducing to the external canal of one ear a controlled change in air presεure; F. determining whether the controlled change in preεsure produces significant reactions in one or more of the measured quantities.

G. repeating proceedures E and F with the εubject in different poεitionε in relation to^' the εway-reference axis; and

H. comparing the extent of correlated reactions to controlled external vestibular stimuli with the subject in different positions in relation to the sway-reference axis.

15. A method, according to claim 14, wherein step A includes the additional step of having the subject close hiε eyeε.

16. A method according to claim 14, wherein εtep A includeε the additional εtep of εubεtantially εurrounding the εubject'ε field of view with a movable viεual encloεure, εtep B includes the additional step of aligning the subject'ε head εuch that the εenεitive axiε of one veεtibular end organ iε aligned with the viεual encloεure εway-reference axis, and step D includes moving the visual enclosure in functional relation to the measured quantity.

17. A method for determining whether a subject maintaining a position in equilibrium while support surface inputs are disrupted has a functional losses selectively affecting the vestibular end organs, such method comprising: A. placing a subject on a movable support surface and having the subject asεume a poεition in equilibrium;

SUBSTITUTE SHEET B. poεitioning the εubject'ε head εuch that the εenεitive axiε of one veεtibular end organ iε aligned with the εway-reference axis;

C. measuring one or more quantities related to the subject'ε diεplacement from the equilibrium poεition;

D. moving the support surface in^"functional relation to the meaεured quantity;

E. introducing a controlled external stimuluε to one ear; F. determining whether the controlled stimulus produces significant correlated reactions in one or more of the measured quantities;

G. repeating steps E and F with the subject'ε head positioned such that the sensitive axes of each veεtibular end organ of the ear is in turn aligned with the sway-reference axis;

H. comparing the correlated reactions produced by controlled external vestibular stimuli with the head in different positionε in relation to the εway-reference axis.

18. A method, according to claim 17, wherein step A includes the additional εtep of having the εubject cloεe the eyes.

19. A method, according to claim 17, wherein εtep A includes the additional step of substantially surrounding the subject's field of view with a movable visual enclosure, step B includeε the additional εtep of aligning the εubject'ε head εuch that the εenεitive axiε of one vestibular end organ iε aligned with the viεual encloεure εway-reference axiε, and εtep D includeε the additional εtep of moving the visual enclosure in functional relation to the measured quantity.

20. A method, according to claim 17, for determining whether losseε in veεtibular end organ functionε are are aεymmetrical between the left and right ears, wherein step G includes the additional step of repeating stepε E and F with the other ear expoεed to the controlled external veεtibular εtimuli and εtep H includeε the additional εtep

SUBSTITUTE SHEET of comparing the correlated reationε produced by εtimulation of the left and right earε.

21. A method for determining whether a εubject maintaining an upright εtanding poεition in equilibrium while εupport εurface orientation inputs in the antero-posterior plane of motion (hereinafter termed AP stance support surface inputε) are diεrupted haε εelective or total functional loεε in veεtibular receptor end organε of one ear, εuch method compriεing: A. placing the εubject in an upright εtanding poεition on a εupport εurface which iε independently rotatable about an axiε co-linear with the ankle joints and having the subject assume a position in equilibrium thereon; B. measuring change in the angular orientation of the εubject'ε center of body gravity in the antero-posterior plane about an axis defined by the ankle joints (hereinafter termed AP stance orientation angle) ;

C. measuring change in position of the vertical force center in the antero-posterior plane (hereinafter termed AP ankle torque) ;

D. introducing controlled external stimuli to an ear;

E. determining whether the controlled external stimuli produce εignificant correlated reactionε in AP ankle torque and AP εtance orientation angle.

F. cauεing the εupport εurface to undergo changeε in angular orientation εo as to be 1/8 times the measured change in AP stance orientation angle, ie the sway-reference gain of 1/8; G. introducing controlled external εtimuli to the ear;

H. determining whether the controlled external εtimuli produce εignificant correlated reactionε in AP ankle torque and AP εtance orientation angle; I. repeating εteps F through H with the sway-referenced gain of subεequent repeatε increased to 1/4, 1/2, and then 1.

SUBSTITUTE SHEET J. comparing correlated reactionε to external εtimuli with the sway-reference gains of 0, 1/8, 1/4, 1/2, and 1.

22. A method, according to claim 21 for determining whether a subject maintaining an upright standing poεition in equilibrium while AP εtance εupport εurface inputε and visual orientation inputs in the antero-posterior plane of motion (hereinafter termed AP stance visual inputs) are disrupted has selective or total functional losε in vestibular receptor end organs of one ear, wherein step A includes the additional step of surrounding the subject*ε field of view with a viεual encloεure which iε independently rotatable about an axiε co-linear with the ankle joints and wherein step F includes the additional step of causing the visual enclosure to undergo changes in angular orientation so as to be 1/8 times the measured change in AP stance orientation angle.

23. A method, according to claim 21 for determining whether a subject maintaining an upright standing position in equilibrium while AP stance support surface inputs are disrupted and visual orientation inputs are eliminated has selective or total functional loss in vestibular receptor end organs of one ear, wherein step A includes the additional step of surrounding the having the subject close the eyeε.

24. A method, according to claim 21, for determining whether functional loεses in veεtibular end organε are total bilateral, total unilateral, partial bilateral, partial unilateral, partial in one ear and total in the other, or normal, wherein εtep J includes the additional step of comapring correlated reactions to external stimulation of the left and right ears under all conditions and then placing subjectε into the following εeparate categorieε: Category I - Bilateral Total Loss (no significant correlated reactions to stimulation of either ear with all combinations of sway reference gains and head positionε in relation to the εway-refe ence axiε) Category II - Bilateral Partial Loεs (correlated reactions to

SUBSTITUTE SHEET εtimulation of each ear in all head poεitionε but with εway-referenced gainε of 1/4 or greater only) Category III - Bilateral Selective Loεεeε (correlated reactionε to stimulation of either ear at sway-reference gains of zero with the head in εome poεitions in relation to the sway-reference axis and at sway-reference gains of 1/4 or greater in other head positionε) Category IV - Unilateral Total Loεε (no correlated reactionε to εtimulation of one ear under any and all combinationε of sway-reference gain 0 and head poεition in relation to the εway-reference axis but correlated reactions to stimulation of the other ear with the support surface and visual enclosure fixed) Category V - Unilateral Partial Losε (correlated reactionε to εtimulation of one ear with the εupport εurface and 5 viεual encloεure fixed and in the other ear only with εway-referenced gainε of 1/4 or greater) Category VI - Unilateral Selective Loεε (correlated reactions to stimulation of one ear at sway-reference gains of zero with the head in some positionε in relation to the o sway-reference axis and at sway-reference gains of 1/4 or greater in other head positionε, and correlated reactionε to stimulation of the other ear with the support surface fixed) Category N (all remaining subjects) .

25. A method for determining whether a subject ₅ maintaining an upright standing position in equilibrium while AP stance support surface inputs and AP εtance viεual inputε are diεrupted haε an abnormal connection between the middle and inner ear εpaceε, εuch method compriεing:

A. placing the εubject in an upright εtanding poεition on a movable support surface which is independently rotatable about an axis co-linear with the ankle jointε and having the εubject assume a poεition in equilibrium;

B. εubεtantially surrounding the subject'ε field of view with a viεual encloεure independently rotatable about an axiε co-linear with the ankle jointε;

SUBSTITUTE SHEET C. meaεuring change in the angular orientation of the subject's center of body gravity in the antero-posterior plane about an axis defined by the ankle joints (hereinafter termed AP stance orientation angle) ; D. causing either one or both of the εupport εurface and viεual encloεure to undergo changes in angular orientation so as to be in proportion to the measured change in AP stance orientation angle, thereby reducing or nullifying changes in angle between the AP stance orientation of the εubject and the inclination of the εupport εurface and visual enclosure;

E. introducing to the external canal of one ear a controlled increase or decrease in air presεure;

F. determining whether the controlled change in pressure produces a significant correlated change in the AP ankle torque and AP stance orientation angle;

26. A method for determining whether a subject maintaining an upright standing position in equilibrium while stance support εurface inputε in the lateral plane of motion (hereinafter termed lateral stance support surface inputs) and viεual inputε in the lateral plane of motion (hereinafter termed lateral viεual inputε) are diεrupted has an abnormal connection between the inner and middle ear spaces, such method comprising: A. placing the subject in an upright standing position on a movable εupport εurface which iε independently rotatable about an axis perpendicular to the ankle joints and having the εubject assume a position in equilibrium; B. substantially surrounding the subj ct'ε field of view with a visual enclosure independently rotatable about an axis perpendicular to the ankle joints;

C. measuring change in the angular orientation of the subject's center of body gravity in the lateral plane about an axis defined by the ankle joints (hereinafter termed lateral εtance orientation angle) and change in the

SUBSTITUTE SHEET poεition of the vertical force center in the lateral direction (hereinafter termed lateral ankle torque) ;

D. cauεing either one or both of the εupport εurface and viεual encloεure to undergo changeε in angular orientation εo aε to be in proportion to the eaεured change in lateral εtance orientation angle, thereby reducing or nullifying changeε in angle between the lateral stance orientation of the εubject and the inclination of the εupport εurface and viεual encloεure; E. introducing to the external canal of one ear a controlled increaεe or decreaεe in air preεεure;

F. determining whether the controlled change in preεεure produceε εignificant correlated changes in lateral ankle torque and lateral εtance orientation angle.

27. A method for determining whether a εubject maintaining an upright εtanding poεition in equilibrium while lateral εtance εupport εurface inputε are diεrupted haε functional loεε in veεtibular receptor end organε of one ear, such method comprising: A. placing the subject in an upright standing position on a support surface which is independently rotatable about an axis perpendicular to the ankle jointε and having the εubject assume a position in equilibrium thereon; B. measuring change in the lateral stance orientation angle and the lateral ankle torque;

C. introducing to one ear controlled external vestibular stimuli;

D.^" determining whether the controlled external stimuli produce significant correlated changes in lateral ankle torque and lateral stance orientation angle.

E. cauεing the εupport εurface to undergo changes in angular orientation so aε to be 1/8 timeε the meaεured change in lateral εtance orientation angle, i.e., the εway-reference gain of 1/8;

F. introducing to one ear controlled external veεtibular εtimuli;

SUBSTITUTE SHEET G. determining whether the controlled external εtimuli produce εignificant correlated changeε in lateral ankle torque and lateral εtance orientation angle. H. repeating εtepε E through G with the εway-referenced gain of εubεequent repeatε increaεed to 1/4, 1/2, and then 1.

28. A method, according to claim 27, for determining whether a subject maintaining an upright εtanding poεition in equilibrium while lateral stance εupport εurface inputs and lateral stance visual inputs are simultaneously disrupted has functional loss in vestibular receptor end organs of one ear, wherein step A includes the additional step of subεtantially εurrounding the εubject'ε field of view with a viεual enclosure independently rotatable about an axis perpendicular to the ankle jointε and wherein εtep E includeε the additional causing the visual enclosure to undergo changes in angular orientation so as to be 1/8 times the measured change in lateral stance orientation angle.

29. A method, according to claim 27, for determining whether a subject maintaining an upright standing position in equilibrium while lateral stance support surface inputs are disrupted and visual orientation inputs eliminated has functional losε in veεtibular receptor end organε of one ear, wherein step A includes the additional εtep of having the subject close the eyes.

30. A method for determining whether a subject maintaining a εeated poεition in equilibrium while εupport εurface orientation inputε in the antero-poεterior plane of motion (hereinafter termed AP εeated εupport εurface inputε) are diεrupted haε functional loεε in the veεtibular receptor end organε of one ear, such method comprising^*-. A. placing the subject in a seated position on a movable support surface which is independently rotatable about an axis co-linear with the hip joints and having the subject assume a position in equilibrium; B. measuring change in the angular orientation of the subject'ε center of body gravity in the antero-poεterior plane about an axiε defined by the hip jointε (hereinafter termed AP εeated orientation angle) and meaεuring the antero-poεterior poεition of the vertical force center of the εubjectε buttockε in contact with the εupport εurface (hereinafter termed AP hip torque) ;

C. cauεing the εupport surface to undergo changes in angular orientation so as to be in proportion to the measured change in AP seated orientation angle, thereby reducing or nullifying changes in angle between the AP seated orientation of the subject and the inclination of the support surface;

D. introducing to one ear controlled external stimuli;

E. determining whether the controlled external stimuli produce εignificant correlated changeε in AP hip torque and AP εeated orientation angle.

31. A method, according to claim 30, for determining whether a εubject maintaining a εeated poεition in equilibrium while AP εeated εupport εurface inputε and AP εeated viεual inputε are εimultaneouεly disrupted has functional losε in the vestibular receptor end organs of one ear, wherein step A includes the additional εtep of εubεtantially εurrounding the εubejct'ε field of view with a viεual encloεure which iε independently rotatable about an axiε co-linear with the hip jointε and wherein εtep C includeε the additional εtep of cauεing the viεual encloεure to undergo angular changeε in orientation εo aε to be in proportion to the meaεured change in AP εeated orientation angle.

32. A method, according to claim 30, for determining whether a εubject maintaining a εeated poεition in equilibrium while AP seated support surface inputs are disrupted and visual orientation inputs are eliminated has functional loss in the vestibular receptor end organs of one ear, wherein εtep A includeε the additional εtep of having the εubject cloεe the eyeε.

33. A method for determining whether a subject maintaining a εeated poεition in equilibrium while AP seated εupport εurface inputε are disrupted has an abnormal connection between the inner and middle ear spaces, such method compriεing:

A. placing the εubject in a εeated poεition on a movable εupport εurface which iε independently rotatable about an axiε co-linear with the hip jointε and having the εubject assume a position in equilibrium;

B. measuring changes in the AP εeated orientation angle and the AP hip torque;

C. cauεing the support εurface to undergo changes in angular orientation so aε to be in proportion to the measured change in AP seated orientation angle, thereby reducing or nullifying changeε in angle between the AP εtance orientation of the εubject and the inclination of the support εurface; D. introducing to one ear controlled changes in pressure to the external ear canal;

E. determining whether the controlled changeε in preεεure produce significant correlated changeε in AP hip torque and AP seated orientation angle.

34. A method, according to claim 33, for determining whether a subject maintaining a seated position in equilibrium while AP seated support surface inputs and AP seated visual inputs are simultaneouεly diεrupted haε an abnormal connection between the inner and middle ear spaces, wherein step A includes the additional εtep of εubstantially surrounding the subejct'ε field of view with a viεual encloεure which iε independently rotatable about an axiε co-linear with the hip jointε and wherein εtep C includeε the additional εtep of cauεing the viεual encloεure to undergo angular changeε in orientation εo aε to be in proportion to the meaεured change in AP εeated orientation angle.

SUBSTITUTE SHEET

35. A method, according to claim 33, for determining whether a εubject maintaining a seated position in equilibrium while AP seated support εurface inputs are diεrupted and viεual orientation inputε are eliminated haε an abnormal connection between the inner and middle ear εpaceε, wherein εtep A includeε the additional εtep of having the εubject cloεe the eyeε.

36. A method for determining whether a εubject maintaining a εitting poεition in equilibrium while AP εeated εupport εurface inputε are diεrupted haε εelective or partial functional loεε in veεtibular receptor end organε of one ear, εuch method compriεing:

A. placing the εubject in a εitting poεition on a εupport εurface which iε independently rotatable about an axiε co-linear with the hip jointε and having the εubject assume a position in equilibrium thereon;

B. measuring change in the AP εeated orientation angle) ;

C. introducing to the one ear controlled external εtimuli;

D. determining whether the controlled external εtimuli produce a significant correlated changes in AP hip torque and AP seated orientation angle;

E. causing the support surface to undergo changes in angular orientation so as to be 1/8 times the measured change in AP stance orientation angle, i.e., the sway-reference gain of 1/8;

F. introducing to one ear controlled external stimuli; G. determining whether the controlled external εtimuli produce εignificant correlated changeε in AP hip torque and AP εeated orientation angle;

H. repeating εtepε E through G with the εway-referenced gain of εubεequent repeatε increaεed to 1/4, 1/2, and then 1;

I. comparing the extent of correlated reactionε with the εway-reference gainε of 0, 1/8, 1/4, 1/2 and 1.

37. A method, according to claim 36, for determining whether a subject maintaining a sitting poεition in equilibrium while AP εeated εupport εurface inputε and AP seated visual inputε are εimultaneouεly diεrupted haε εelective or partial functional loεε in veεtibular receptor end organs of one ear, wherein εtep A includeε the additional step of substantially surrounding the εubject'ε field of view with a viεual encloεure independently rotatable about an axis co-linear with the hip jointε and εtep E includeε the additional εtep of cauεing viεual enclosure to undergo changes in angular orientation εo aε to be 1/8 timeε the meaεured change in AP εtance orientation angle.

38. A method, according to claim 36, for determining whether a subject maintaining a εitting poεition in equilibrium while AP εeated support surface inputs are disrupted and visual inputs eliminated has selective or partial functional loss in vestibular receptor end organε of one ear, wherein εtep A includeε the additional εtep of having the subject close the eyeε.

39. A method, according to claim 36, for determining whether functional loεseε in veεtibular end organε are total bilateral, total unilateral, partial bilateral, partial unilateral, partial in one ear and total in the other, or normal, wherein εtep J includes the additional step of comapring correlated reactions to external stimulation of the left and right ears under all conditions and then placing subjects into the following separate categories: Category I - Bilateral Total Loss (no significant correlated reactions to stimulation of either ear with all combinations of sway reference gainε and head positions in relation to the sway-reference axis) Category II - Bilateral Partial Losε (correlated reactionε to εtimulation of each ear in all head positions but with sway-referenced gains of 1/4 or greater only) Category III - Bilateral Selective Losεeε (correlated reactionε to εtimulation of either ear at εway-reference gainε of zero with the head in εome poεitionε in relation to the εway-reference axiε and at εway-reference gainε of 1/4 or greater in other head poεitionε) Category IV - Unilateral Total Loεε (no correlated reaσtionε to εtimulation of one ear under any and all combinationε of εway-reference gain and head poεition in relation to the εway-reference axiε but correlated reactionε to εtimulation of the other ear with the εupport εurface and viεual encloεure fixed) Category V - Unilateral Partial Loεε (correlated reactionε to stimulation of one ear with the support surface and viεual encloεure fixed and in the other ear only with εway-referenced gainε of 1/4 or greater) Category VI - Unilateral Selective Loεε (correlated reactionε to εtimulation of one ear at εway-reference gainε of zero with the head in εome poεitionε in relation to the εway-reference axiε and at εway-reference gainε of 1/4 or greater in other head poεitions, and correlated reactions to εtimulation of the other ear with the εupport surface fixed) Category N (all remaining subjects) .

40. A method for determining on a selective basis the responεiveneεε of individual inner ear veεtibular end organε to an external εtimuluε in a εubject placed in a poεition of equilibrium and maintaining thiε poεition while εupport εurface inputε are diεrupted, such method comprising:

A. placing the subject on a movable support surface and having the εubject assume a position in equilibrium thereon;

B. positioning the εubject in relation to the sway-reference axis such that the senεitive axeε of one or more vestibular end organs are selectively aligned with the sway-reference axis;

C. meaεuring one or more quantitieε related to the εubject'ε displacement from the equilibrium position; D. making the movable support surface compliant about the sway-reference axis of motion;

SUBSTITUTE SHEET E. introducing to one ear or both earε εimultaneouεly a controlled external veεtibular εtimuluε;

F. determining whether or not the controlled external stimuluε produceε εignificant correlated changeε in one or more of the meaεured quantitieε.

G. repeating proceedureε E and F-with the subject in different positionε in relation to the sway-reference axiε; and

H. comparing the extent of correlated changeε to controlled external veεtibular εtimuli with the subject in different positions in relation to the sway-reference axiε.

41. A method, according to claim 40, for εelectively determining the reεponεiveneεε of individual veεtibular end organ receptorε to an external εtimuluε while both εupport surface inputε and viεual inputε are diεrupted, wherein step A includes the additional step of subεtanially εurrounding the εubject'ε field of view with a εecond visual encloεure and εtep C includes the additional εtep of attaching the viεual enclosure to the compliant support surface such that the two rotate together about the εame εway-reference axis.

42. A method, according to claim 40, for selectively determining the responsiveneεε of individual veεtibular end organ receptorε to an external εtimuluε in a εubject with εupport εurface inputε diεrupted and deprived of viεual inputε, wherein εtep A includeε the additional εtep of having the εubject close his eyes.

43. A method for determining in a subject placed in a position of equilibrium and maintaining this poεition while both εupport εurface and viεual inputε are diεrupted haε an abnormal connection between the middle and inner ear εpace, such method comprising:

A. placing the subject on a movable support surface and having the εubject assume a position in equilibrium; B. substantially surrounding the subj ct'ε field of view with a movable viεual encloεure;

SUBSTITUTE SHEET C. measuring one or more quantities related to the subject's displacement from the equilibrium position;

D. making the support surface compliant about the sway-reference axis of motion and attaching the visual enclosure to the support εurface such that the two surfaces rotate together about the εame sway-reference axis;

E. introducing to the external canal of one ear a controlled change in air presεure;

F. determining whether the controlled change in pressure causes significant change in one or more of the measured quantitieε.

44. A method for determining whether a εubject maintaining a poεition in equilibrium while support surface inputs are disrupted has an abnormal connection between the middle and inner ear space selectively affecting the vestibular end organs, εuch method compriεing:

A. placing a εubject on a movable εupport surface and having the subject asεume a poεition in equilibrium;

B. poεitioning the εubject,ε head εuch that the εenεitive axiε of one veεtibular end organ of the ear iε aligned with the εway-reference axiε;

C. meaεuring one or more quantitieε related to the εubject'ε diεplacement from the equilibrium poεition;

D. making the movable εupport surface compliant about the sway-reference axis of motion;

F. determining whether the controlled change in preεεure produceε εignificant reactionε in one or more of^" the meaεured quantitieε.

G. repeating proceedureε E and F with the εubject in different poεitionε in relation to the εway-reference axiε; and

H. comparing the extent of correlated reactions to controlled external vestibular stimuli with the subject in different positionε in relation to the εway-reference axis.

SUBSTITUTE SHEET

45. A method, according to claim 44, wherein step A includes the additional εtep of having the εubject cloεe hiε eyeε.

46. A method according to claim 44, wherein εtep A includes the additional step of εubstantially surrounding the subject's field of view with a movable visual encloεure, step B includes the additional step of aligning the subject's head such that the sensitive axis of one vestibular end organ is aligned with the visual enclosure sway-reference axis, and step D includes the additional step of attaching the viεual encloεure to the εupport surface εuch that the two rotate together about the same sway-reference axis.

47. A method for determining whether a subject maintaining a position in equilibrium while support surface inputε are diεrupted haε a functional losseε εelectively affecting the veεtibular end organε, such method comprising:

A. placing a subject on a movable support surface and having the subject asεume a poεition in equilibrium;

B. poεitioning the εubject,ε head εuch that the sensitive axis of one vestibular end organ is aligned with the εway-reference axis;

C. measuring one or more quantities related to the subject'ε displacement from the equilibrium position;

D. making the support surface compliant about the axiε of εway-reference motion;

E. introducing a controlled external εtimuluε to one ear; F. determining whether the controlled εtimuluε produceε significant correlated reactions in one or more of the measured quantities;

G. repeating εtepε E and F with the εubject'ε head poεitioned εuch that the εenεitive axeε of each veεtibular end organ of the ear iε in turn aligned with the εway-reference axiε; H. comparing the correlated reactionε produced by controlled external veεtibular εtimuli with the head in different poεitions in relation to the εway-reference axiε.

48. A method, according to claim 47, wherein εtep A includeε the additional εtep of having the εubject cloεe the eyeε.

49. A method, according to claim 47, wherein εtep A includeε the additional step of subεtantially εurrounding the εubject'ε field of view with a movable viεual ₀ encloεure, εtep B includes the additional step of aligning the εubject'ε head εuch that the εenεitive axiε of one vestibular end organ is aligned with the visual enclosure εway-reference axiε, and εtep D includeε the additional εtep of attaching the viεual encloεure to the compliant ₅ εupport εurface εuch that the two rotate together about the εame εway-reference axiε.

50. A method, according to claim 47, for determining whether loεεeε in veεtibular end organ functionε are are aεymmetrical between the left and right ears, wherein step o G includes the additional step of repeating stepε E and F with the other ear expoεed to the controlled external veεtibular εtimuli and εtep H includeε the additional εtep of comparing the correlated reationε produced by εtimulation of the left and right earε.

51. A method for determining whether a εubject maintaining an upright standing position in equilibrium while AP stance support .surface inputε are diεrupted haε εelective or total functional loεε in veεtibular receptor end organε of one ear, εuch method compriεing: A. placing the εubject in an upright εtanding poεition on a εupport εurface which iε independently rotatable about an axiε co-linear with the ankle jointε and having the εubject assume a position in equilibrium thereon; B. measuring change in the AP stance orientation angle;

C. measuring change in AP ankle torque; D. introducing controlled external stimuli to an ear;

E. determining whether the controlled external stimuli produce εignificant correlated reactionε in AP ankle torque and AP εtance orientation angle. F. cauεing the εupport εurface to undergo changeε in compliance about the εway-reference axis of rotation so that to surface yields by an angle approximately 1/8 times the AP stance orientation angle of the subject (hereinafter termed the support surface compliance gain) ; G. introducing controlled external stimuli to the ear;

H. determining whether the controlled external stimuli produce significant correlated reactions in AP ankle torque and AP stance orientation angle; I. repeating εtepε F through H with the εupport surface compliance gain increased to 1/4, 1/2, and then 1.

J. comparing correlated reactionε to external εtimuli with the support εurface compliance gain εet to 0, 1/8, 1/4, 1/2, and 1.

52. A method, according to claim 51 for determining whether a εubject maintaining an upright εtanding poεition in equilibrium while AP εtance εupport εurface inputε and AP εtance viεual inputs are disrupted has selective or total functional losε in veεtibular receptor end organε of one ear, wherein εtep A includeε the additional εtep of εurrounding the subject's field of view with a visual enclosure which is attached to the support surface such that the two surfaceε rotate together about the εame εway-reference axiε.

53. A method, according to claim 51 for determining whether a εubject maintaining an upright standing position in equilibrium while AP stance support εurface inputs and AP stance visual inputs are eliminated haε εelective or total functional loεε in veεtibular receptor end organs of one ear, wherein εtep A includeε the additional εtep of having the εubject cloεe the eyeε.

54. A method, according to claim 51, for determining whether functional loεεeε in veεtibular end organε are total bilateral, total unilateral, partial bilateral, partial unilateral, partial in one ear and total in the other, or normal, wherein step J includeε the additional εtep of comapring correlated reactionε-to external εtimulation of the left and right earε under all conditions and then placing subjectε into the following εeparate categorieε: Category I - Bilateral Total Loεε (no εignificant correlated reactionε to stimulation of either ear with all combinations of support surface compliance gains and head positionε in relation to the εway-reference axis) Category II - Bilateral Partial Losε (correlated reactionε to εtimulation of each ear in all head poεitionε but with εupport εurface compliance gainε of 1/4 or greater only) Category III - Bilateral Selective Loεses (correlated reactionε to εtimulation of either ear at εupport εurface compliance gainε of zero with the head in εome poεitionε in relation to the εway-reference axiε and at εupport εurface compliance gainε of 1/4 or greater in other head poεitionε) Category IV - Unilateral Total Loεε (no correlated reactionε to εtimulation of one ear under any and all combinationε of εupport εurface compliance gain and head poεition in relation to the εway-reference axiε but correlated reactionε to εtimulation of the other ear with the εupport εurface and viεual enclosure fixed) Category V - Unilateral Partial Losε (correlated reactionε to εtimulation of one ear with the εupport εurface and viεual encloεure fixed and in the other ear only with εupport εurface compliance gainε of 1/4 or greater) Category VI - Unilateral Selective Loεε (correlated reactionε to εtimulation of one ear at εupport εurface compliance gainε of zero with the head in εome poεitions in relation to the sway-reference axis and at support surface compliance gains of 1/4 or greater in other head positionε, and correlated reactionε to εtimulation of the other ear with the εupport εurface fixed) Category N (all remaining εubjectε) .

SUBSTITUTE SHEET

55. A method for determining whether a subject maintaining an upright standing position in equilibrium while AP stance support surface inputs and AP εtance viεual inputε are diεrupted haε an abnormal connection between the middle and inner ear εpaces, such method comprising:

A. placing the εubject in an upright standing position on a movable support surface which is independently rotatable about an axis co-linear with the ankle joints and having the subject assume a position in ₀ equilibrium;

B. substantially surrounding the subject'ε field of view with a viεual encloεure independently rotatable about an axis co-linear with the ankle joints;

C. measuring change in the AP stance orientation ₁₅ angle;

D. making the support surface compliant about the sway reference axis of rotation and then either fixing the visual enclosure or attaching it to the support surface εuch that both rotate about the εame εway-reference axiε,

2o thereby reducing or nullifying changes in angle between the AP stance orientation angle of the subject and the inclination of the support surface alone or the support surface and visual enclosure together;

E. introducing to the external canal of one ear a __ controlled increase or decrease in air pressure;

F. determining whether the controlled change in pressure produces a significant correlated change in the AP ankle torque and AP εtance orientation angle;

56. A method for determining whether a εubject

30 maintaining an upright standing poεition in equilibrium while lateral εtance εupport εurface inputε and lateral εtance viεual inputε are diεrupted haε an abnormal connection between the inner and middle ear spaces, such method comprising:

35 A. placing the subject in an upright standing position on a movable support surface which iε independently rotatable about an axiε perpendicular to the

SUBSTITUTE SHEET ankle jointε and having the εubject assume a position in equilibrium;

B. substantially surrounding the subject's field of view with a visual enclosure independently rotatable about an axis perpendicular to the ankle joints;

C. measuring change in the lateral εtance orientation angle and change in the lateral ankle torque;

D. making the εupport surface compliant about the sway reference axis of rotation and either fixing the 0 visual enclosure or attaching it to the support εurface εuch that both rotate together about the εame εway-reference axiε, thereby reducing or nullifying changes in angle between the lateral εtance orientation angle of the εubject and the inclination of the support εurface ₅ alone of the support surface and visual enclosure together;

F. determining whether the controlled change in preεεure produceε εignificant correlated changeε in lateral o ankle torque and lateral εtance orientation angle.

57. A method for determining whether a subject maintaining an upright εtanding poεition in equilibrium while lateral εtance εupport εurface inputε are disrupted haε functional loεε in veεtibular receptor end organε of 5 one ear, εuch method compriεing:

A. placing the subject in an upright standing position on a support surface which is independently rotatable about an axis perpendicular to the ankle jointε and having the εubject assume a position in equilibrium o thereon;

B. measuring change in the lateral stance orientation angle and the lateral ankle torque;

C. introducing to one ear controlled external vestibular stimuli; D. determining whether the controlled external stimuli produce significant correlated^'changes in lateral ankle torque and lateral stance orientation angle.

SUBSTITUTE SHEET E. causing the εupport εurface to undergo changeε in εupport εurface compliance gain εuch that the εurface yieldε by an angle 1/8 timeε the change in lateral εtance orientation angle; F. introducing to one ear controlled external veεtibular stimuli;

G. determining whether the controlled external εtimuli produce significant correlated changeε in lateral ankle torque and lateral εtance orientation angle. ₀ H. repeating εtepε E through G with the εupport εurface compliance gain of εubεequent repeatε increaεed to 1/4, 1/2, and then 1.

58. A method, according to claim 57, for determining whether a subject maintaining an upright εtanding poεition

,₅ in equilibrium while lateral εtance εupport surface inputε and lateral εtance viεual inputε are εimultaneouεly diεrupted haε functional loεε in veεtibular receptor end organε of one ear, wherein εtep A includeε the additional εtep of εubεtantially surrounding the εubject'ε field of

₂₀ view with a viεual encloεure attached to the εupport εurface εuσh that the two εurfaceε rotate together about the εame εway-reference axiε.

59. A method, according to claim 57, for determining whether a εubject maintaining an upright standing position

2 in equilibrium while lateral stance support surface inputs are disrupted and visual inputs eliminated has functional losε in veεtibular receptor end organε of one ear, wherein εtep A includeε the additional εtep of having the subject close the eyes.

₃₀

60. A method for determining whether a subject maintaining a seated position in equilibrium while AP seated support εurface inputs are diεrupted haε functional loεε in the veεtibular receptor end organs of one ear, such method comprising:

₃5 A. placing the εubject in a εeated position on a movable support surface which is independently rotatable

SUBSTITUTE SHEET about an axiε co-linear with the hip jointε and having the εubject assume a position in equilibrium;

B. meaεuring change in the AP εeated orientation angle and meaεuring the AP hip torque;

5 C. making the εupport εurface compliant about the rotatable εway-reference axiε, thereby- reducing or nullifying changeε in angle between the AP εeated orientation angle of the εubject and the inclination of the εupport εurface;

₁₀ D. introducing to one ear controlled external εtimuli;

E. determining whether the controlled external εtimuli produce significant correlated changes in AP hip torque and AP seated orientation angle.

₁₅

61. A method, according to claim 60, for determining whether a subject maintaining a seated position in equilibrium while AP seated support surface inputs and AP εeated viεual inputε are εimultaneouεly diεrupted haε functional loεε in the veεtibular receptor end organε of

_ one ear, wherein εtep A includeε the additional εtep of εubεtantially εurrounding the εubejct'ε field of view with a viεual enclosure which is fixed to rotate together with the εupport εurface.

62. A method, according to claim 60, for determining -_ whether a εubject maintaining a seated position in equilibrium while AP seated support surface inputs are disrupted and viεual orientation inputε are eliminated haε functional loεε in the veεtibular receptor end organε of one ear, wherein εtep A includeε the additional εtep of _3Q having the εubject cloεe the eyeε.

63. A method for determining whether a εubject maintaining a εeated poεition in equilibrium while AP seated support surface inputs are disrupted has an abnormal connection between the inner and middle ear spaceε, εuch-

__ method comprising:

A. placing the subject in a seated position on a movable support surface which iε independently rotatable

SUBSTITUTE SHEET about an axiε co-linear with the hip jointε and having the εubject assume a poεition in equilibrium;

B. meaεuring changeε in the AP εeated orientation angle and the AP hip torque; C. making the εupport εurface compliant about the εway-reference axiε of rotation, thereby reducing or nullifying changeε in angle between the AP seated orientation of the subject and the inclination of the support surface; D. introducing to one ear controlled changes in pressure to the external ear canal;

E. determining whether the controlled changes in pressure produce significant correlated changes in AP hip torque and AP seated orientation angle.

64. A method, according to claim 63, for determining whether a subject maintaining a seated position in equilibrium while AP seated support surface inputε and AP εeated visual inputs are simultaneously disrupted haε an abnormal connection between the inner and middle ear εpaces, wherein εtep A includeε the additional εtep of εubεtantially surrounding the εubejct'ε field of view with a visual enclosure which is fixed to rotate together with the compliant εupport surface.

65. A method, according to claim 63, for determining whether a εubject maintaining a seated position in equilibrium while AP seated εupport εurface inputε are diεrupted and viεual orientation inputε are eliminated has an abnormal connection between the inner and middle ear spaces, wherein step A includes the additional εtep of having the εubject cloεe the eyeε.

66. A method for determining whether a εubject maintaining an upright εitting poεition in equilibrium while AP εeated εupport εurface inputε are diεrupted haε εelective or total functional loss in vestibular receptor end organs of one ear, such method comprising:

A. placing the subject in an upright sitting position on a support surface which is independently rotatable about

SUBSTITUTE SHEET an axis co-linear with the hip joints and having the εubject assume a position in equilibrium thereon;

B. measuring change in the AP εeated orientation angle; C. meaεuring change in AP hip torque;

D. introducing controlled external εtimuli to an ear;

E. determining whether the controlled external εtimuli produce εignificant correlated reactionε in AP hip torque and AP εeated orientation angle. ^F« cauεing the εupport εurface to undergo changes in compliance about the sway-reference axis of rotation so that to surface yields by an angle approximately 1/8 times the AP seated orientation angle of the subject (hereinafter termed the support surface compliance gain) ; G. introducing controlled external stimuli to the ear;

H. determining whether the controlled external stimuli produce significant correlated reactionε in AP hip torque and AP εeated orientation angle;

I. repeating εtepε F through H with the εupport surface compliance gain increased to 1/4, 1/2, and then 1.

J. comparing correlated reactions to external εtimuli with the support εurface compliance gain set to 0, 1/8, 1/4, 1/2, and 1.

67. A method, according to claim 66 for determining whether a subject maintaining an upright sitting position in equilibrium while AP εeated εupport εurface inputε and AP εeated viεual inputε are diεrupted haε εelective or total functional loss in vestibular receptor end organs of one ear, wherein step A includes the additional step of surrounding the εubject'ε field of view with a viεual encloεure which iε attached to the support surface εuch that the two εurfaceε rotate together about the εame εway-reference axiε.

68. A method, according to claim 66 for determining whether a εubject maintaining an upright sitting position in equilibrium while AP seated support surface inputs

SUBSTITUTE SHEET diεrupted and AP seated viεual orientation inputε are eliminated haε εelective or total functional loεε in veεtibular receptor end organε of one ear, wherein εtep A includeε the additional εtep of having the εubject cloεe the eyes.

69. A method, according to claim- 66, for determining whether functional losses in vestibular end organε are total bilateral, total unilateral, partial bilateral, partial unilateral, partial in one ear and total in the other, or normal, wherein εtep J includes the additional step of comapring correlated reactionε to external stimulation of the left and right ears under all conditions and then placing subjects into the following separate categories: Category I - Bilateral Total Loss (no significant correlated reactions to stimulation of either ear with all combinations of support surface compliance gains and head positions in relation to the sway-reference axis) Category II - Bilateral Partial Losε (correlated reactionε to εtimulation of each ear in all head poεitions but with support surface compliance gains of 1/4 or greater only) Category III - Bilateral Selective Losses (correlated reactions to stimulation of either ear at support surface compliance gains of zero with the head in some positions in relation to the sway-reference axis and at support εurface compliance gains of 1/4 or greater in other head positionε) Category IV - Unilateral Total Loεε (no correlated reactionε to εtimulation of one ear under any and all combinationε of εupport surface compliance gain and head position in relation to the sway-reference axis but correlated reactions to stimulation of the other ear with the support surface and visual enclosure fixed) Category V - Unilateral Partial Losε (correlated reactionε to εtimulation of one ear with the εupport εurface and visual enclosure fixed and in the other ear only with support surface compliance gains of 1/4 or greater) Category VI - Unilateral Selective Losε (correlated reactionε to εtimulation of one ear at εupport εurface compliance gainε

SUBSTITUTE SHEET of zero with the head in εome poεitionε in relation to the sway-reference axis and at support surface compliance gainε of 1/4 or greater in other head poεitionε, and correlated reactionε to εtimulation of the other ear with the εupport surface fixed) Category N (all remaining subjectε) .

SUBSTITUTE SHEET