Vertical linear self-motion perception during visual and inertial motion: more than weighted summation of sensory inputs

We evaluated visual and vestibular contributions to vertical self motion perception by exposing subjects to various combinations of 0.2 Hz vertical linear oscillation and visual scene motion. The visual stimuli presented via a head-mounted display consisted of video recordings of the test chamber from the perspective of the subject seated in the oscillator. In the dark, subjects accurately reported the amplitude of vertical linear oscillation with only a slight tendency to underestimate it. In the absence of inertial motion, even low amplitude oscillatory visual motion induced the perception of vertical self-oscillation. When visual and vestibular stimulation were combined, self-motion perception persisted in the presence of large visual-vestibular discordances. A dynamic visual input with magnitude discrepancies tended to dominate the resulting apparent self-motion, but vestibular effects were also evident. With visual and vestibular stimulation either spatially or temporally out-of-phase with one another, the input that dominated depended on their amplitudes. High amplitude visual scene motion was almost completely dominant for the levels tested. These findings are inconsistent with self-motion perception being determined by simple weighted summation of visual and vestibular inputs and constitute evidence against sensory conflict models. They indicate that when the presented visual scene is an accurate representation of the physical test environment, it dominates over vestibular inputs in determining apparent spatial position relative to external space.     

Influence of visually induced self-motion on postural stability

CONCLUSION: Our results indicate that the illusion of self-motion is a significant factor leading to spatial disorientation. OBJECTIVE: Under normal circumstances, self-motion is perceived in response to motion of the head and body. However, under certain conditions, such as virtual reality environments, visually induced self-motion can be perceived even though the subject is not actually moving, a phenomenon known as "vection". The aim of this study was to examine the possible influence of illusory self-rotation (circular vection) on postural adjustments. MATERIAL AND METHODS: The subjects were 10 young females with no history of ocular or vestibular disease. Video-motion analysis was applied to measure postural movements during vertical optokinetic stimulation. RESULTS: For most subjects, movement of the visual surroundings induced head and body displacements in the same direction as that of the visual stimulus, regardless of the onset of self-motion perception. However, there was a significant increase in postural instability after the subjects began to perceive false self-motion in the opposite direction to that of the visual stimulus.     

Baselines for three-dimensional perception of combined linear and angular self-motion with changing rotational axis

The laws of physics explain many human misperceptions of whole-body passive self-motion. One classic misperception occurs in a rotating chair in the dark: If the chair is decelerated to a stop after a period of counterclockwise rotation, then a subject will typically perceive clockwise rotation. The laws of physics show that, indeed, a clockwise rotation would be perceived even by a perfect processor of angular acceleration information, assuming that the processor is initialized (prior to the deceleration) with a typical subject's initial perception - of no rotation in this case. The motion perceived by a perfect acceleration processor serves as a baseline by which to judge human self-motion perception; this baseline makes a rough prediction and also forms a basis for comparison, with uniquely physiological properties of perception showing up as deviations from the baseline. These same principles, using the motion perceived by a perfect acceleration processor as a baseline, are used in the present paper to investigate complex motions that involve simultaneous linear and angular accelerations with a changing axis of rotation. Baselines - motions that would be perceived by a perfect acceleration processor, given the same initial perception (prior to the motion of interest) as that of a typical subject - are computed for the acceleration and deceleration stages of centrifuge runs in which the human carriage tilts along with the vector resultant of the centripetal and gravity vectors. The computations generate a three-dimensional picture of the motion perceived by a perfect acceleration processor, by simultaneously using all six interacting degrees of freedom (three angular and three linear) and taking into account the non-commutativity of rotations in three dimensions. The resulting three-dimensional baselines predict stronger perceptual effects during deceleration than during acceleration, despite the equal magnitudes (with opposite direction) of forces on the subject during acceleration and deceleration. For a centrifuge run with the subject facing tangentially in the direction of motion, the deceleration baseline shows a perception of forward tumble (pitch rotation) beginning with ascent from the earth, while the acceleration baseline does not have analogous pitch and vertical motion. These results give a three-dimensional explanation for certain puzzling acceleration-deceleration perceptual differences observed experimentally by Guedry, Rupert, McGrath, and Oman (Journal of Vestibular Research, 1992.). The present analysis is consistent with, and expands upon, previous analyses of individual components of motion.     

A comparison of the latencies of visually induced postural change and self-motion perception.

This study compared the latencies of visually induced postural change and self-motion perception under identical visual conditions. The results showed that a visual roll stimulus elicits postural tilt in the direction of scene motion and an increase in postural instability several seconds before the subject begins to perceive illusory self-motion (vection) in the opposite direction. Postural and vection latencies correlate highly with one another, but bear little relationship with the magnitude of either sway or vection.     

Directional preponderance in pitch circular vection

We used optokinetic stimulation (OKS) in eighteen normal adults aged 18-30 years to investigate vertical self-motion perception. In order to induce self-rotation, either a stripe pattern or a random dot pattern was projected onto the inner wall of a hemispherical dome with a diameter of 150 cm. The pattern was rotated either about the subject's vertical axis (yaw) or about the subject's interaural axis (pitch) for 80 s at a constant acceleration of 1 deg/s2. Stimuli were randomly repeated three to four times in each direction. The latency of onset as well as the perceived intensity of circular vection (CV) was measured for each stimulus presentation. CV latencies for upward rotational stimulation were significantly longer than those for downward rotational stimulation under both types of stimulus conditions. There was no significant difference in CV latency between rightward and leftward rotational stimulation. For most subjects, the magnitudes of the perceived CV for rightward rotational stimulation were equal to those for leftward rotational stimulation, whereas the magnitudes of the perceived CV for vertical stimulation showed large intersubject variability. These results provide additional evidence that fundamental differences exist between different types of self-motion. Possible explanations for the directional asymmetry in vertical perception of self-motion will also be discussed.     

Influence of visually induced self-motion on postural stability

Conclusion Our results indicate that the illusion of self-motion is a significant factor leading to spatial disorientation.

Objective Under normal circumstances, self-motion is perceived in response to motion of the head and body. However, under certain conditions, such as virtual reality environments, visually induced self-motion can be perceived even though the subject is not actually moving, a phenomenon known as “vection”. The aim of this study was to examine the possible influence of illusory self-rotation (circular vection) on postural adjustments.

Material and methods The subjects were 10 young females with no history of ocular or vestibular disease. Video-motion analysis was applied to measure postural movements during vertical optokinetic stimulation.

Results For most subjects, movement of the visual surroundings induced head and body displacements in the same direction as that of the visual stimulus, regardless of the onset of self-motion perception. However, there was a significant increase in postural instability after the subjects began to perceive false self-motion in the opposite direction to that of the visual stimulus.     

Rezeptorfunktion der Bogeng?nge

The perception and conversion of motion stimuli by the vestibular receptors, unimpaired postural control and intact visual acuity are essential for spatial orientation. Disturbances in these three sensory systems can manifest as ??vertigo??, ??dizziness?? or ??imbalance??. The integrity of peripheral receptor function, especially of the three semicircular canals, plays a superficial role. They are sensitive to acceleration stimuli, which they transmit via reflexes to the eye muscles. The stabilization of a visual target is via vestibulo-ocular reflexes, which have a very short latency and thus ensure a permanently stable image on the retina. Modern lateral-specific testing procedures are available to diagnose the receptor function of the peripheral vestibular system. The function of the semicircular canals can be analyzed using a head impulse test (HIT) and, more recently, by means of video-HIT as well as on the basis of a caloric test. Using these techniques, all three semicircular canals can be assessed in a side- and receptor-specific manner.     

Receptor function of the semicircular canals: Part 1: anatomy, physiology, diagnosis and normal findings

The perception and conversion of motion stimuli by the vestibular receptors, unimpaired postural control and intact visual acuity are essential for spatial orientation. Disturbances in these three sensory systems can manifest as "vertigo", "dizziness" or "imbalance". The integrity of peripheral receptor function, especially of the three semicircular canals, plays a superficial role. They are sensitive to acceleration stimuli, which they transmit via reflexes to the eye muscles. The stabilization of a visual target is via vestibulo-ocular reflexes, which have a very short latency and thus ensure a permanently stable image on the retina. Modern lateral-specific testing procedures are available to diagnose the receptor function of the peripheral vestibular system. The function of the semicircular canals can be analyzed using a head impulse test (HIT) and, more recently, by means of video-HIT as well as on the basis of a caloric test. Using these techniques, all three semicircular canals can be assessed in a side- and receptor-specific manner.     

How to use body tilt for the simulation of linear self motion

We examined to what extent body tilt may augment the perception of visually simulated linear self acceleration. Fourteen subjects judged visual motion profiles of fore-aft motion at four different frequencies between 0.04-0.33 Hz, and at three different acceleration amplitudes (0.44, 0.88 and 1.76 m/s(2)). Simultaneously, subjects were tilted backward and forward about their pitch axis. The amplitude of pitch tilt was systematically varied. Using a two-alternative-forced-choice paradigm, psychometric curves were calculated in order to determine: 1) the minimum tilt amplitude required to generate a linear self-motion percept in more than 50% of the cases, and 2) the maximum tilt amplitude at which rotation remains sub-threshold in more than 50% of the cases. The results showed that the simulation of linear self motion became more realistic with the application of whole body tilt, as long as the tilt rate remained under the detection threshold of about 3 deg/s. This value is in close agreement with the empirical rate limit commonly used in flight simulation. The minimum required motion cue was inversely proportional to stimulus frequency, and increased with the amplitude of the visual displacement (rather than acceleration). As a consequence, the range of useful tilt stimuli became more critical with increasing stimulus frequency. We conclude that this psychophysical approach reveals valid parameters for motion driving algorithms used in motion base simulators.     

Optokinetic and vestibular interactions with smooth pursuit: psychophysical responses.

The effect was evaluated in normal subjects of the subjective perception of motion of a small visual target (VT) when combined with the effect of vestibular stimulation produced by different magnitudes of constant angular accelerations in the dark or the effect of optokinetic stimulation produced by different constant velocities of rotation. The visual target appeared to the subject to travel more slowly and for a shorter duration when it moved in the direction of the body's angular acceleration or against that of the optokinetic drum. The perceived error in motion was: (i) in the same direction as the subject's motion sensation produced by either of the two stimuli, and (ii) quantitatively related, although differently, to the magnitude of each of the two stimulus modalities; an heuristic model is proposed to account for these observations.     

Influence of fixation on circular vection

The contribution of fixation to latency of circular vection (CV) was examined in twenty-five normal adults aged 18-30 years. For induction of self-motion a random dot pattern was projected onto a hemispherical dome. The pattern was rotated either about the subject's vertical axis or about their interaural axis at a constant acceleration of 1 deg/s2. For the group tested, the perceived CV latencies were significantly shorter with fixation than without fixation in both horizontal and vertical CV. The effect of fixation was pronounced in subjects with longer latencies. The mean CV latencies for two different fixation points between the subject's eyes and the moving pattern did not differ significantly. Our results suggest that the potential influence of fixation must be carefully controlled in studies of visually induced self-motion. Possible explanations for the effect of fixation on the generation of CV will also be discussed.     

Motion sickness susceptibility and the utilisation of visual and otolithic information for orientation

Summary Movement of large portions of the visual field can induce a static observer to experience illusory self-motion, changes in perceived orientation and motion sickness. Two experiments were performed to determine whether susceptibility to motion sickness might be related to an inability to ignore misleading visual information for orientation, measured here in terms of the magnitude of the apparent tilt of the vertical induced by rotation of the visual field about the line of sight. Significant and additive effects of sex and motion sickness susceptibility were demonstrated. Females susceptible to motion sickness proved highly inaccurate when attempting to set a line to the vertical with rotation of the background, while males resistant to motion sickness were the most accurate at this task. Two possible explanations are discussed, the first suggesting subclinical intersubject differences in otolithic sensitivity, and the second postulating deficiencies in intersensory integration. Parallels are drawn with the patterns of multisensory coordination for postural orientation seen in children and in patients with benign paroxysmal positional vertigo.     

One second interval production task during post-rotatory sensation

Temporal intervals production of one second was found to be more variable during self-motion compared to no motion situations. Moreover, the temporal intervals production rhythm during self-motion deceleration decreased whereas it increased during self-motion acceleration, whatever the direction of motion. As somatosensory cues were not excluded in this previous experiment, we now examined whether the same temporal perturbation would occur without variable somatosensory information. In order to isolate the contribution of the vestibular system from that of the somatosensory system, the participants were required to perform a one second temporal interval production task (pressing a button each second) during the post-rotatory illusion following self-rotation. The intervals produced during the vestibular illusion were compared to those produced before the imposed rotation and during self-motion. The production regularity was affected as the temporal intervals were more variable with vestibular stimulation (real and illusory self-motion) than without. Furthermore, during post-rotatory illusion, the production rhythm decreased along the trial, as it was observed during self-motion deceleration. These findings suggest that vestibular stimulation (even vestibular illusion) impaired time estimation.     

The influence of an immersive virtual environment on the segmental organization of postural stabilizing responses

We examined the effect of a 3-dimensional stereoscopic scene on segmental stabilization. Eight subjects participated in static sway and locomotion experiments with a visual scene that moved sinusoidally or at constant velocity about the pitch or roll axes. Segmental displacements, Fast Fourier Transforms, and Root Mean Square values were calculated. In both pitch and roll, subjects exhibited greater magnitudes of motion in head and trunk than ankle. Smaller amplitudes and frequent phase reversals suggested control of the ankle by segmental proprioceptive inputs and ground reaction forces rather than by the visual-vestibular signals. Postural controllers may set limits of motion at each body segment rather than be governed solely by a perception of the visual vertical. Two locomotor strategies were also exhibited, implying that some subjects could override the effect of the roll axis optic flow field. Our results demonstrate task dependent differences that argue against using static postural responses to moving visual fields when assessing more dynamic tasks.     

Perception of horizontal head and trunk rotation in patients with loss of vestibular functions.

In patients with loss of vestibular functions, we studied psychophysically the self-motion perception for 'trunk in space' and 'head in space' during various combinations of horizontal head and trunk rotation in the dark. The results were compared to those of normal subjects. For their 'trunk in space' perception, the subjects relied on their internal image of space, derived from the vestibular receptors in the head, and referred their trunk to this as a reference by adding to it a nuchal trunk-to-head signal. The patients, by contrast, always considered the trunk as stationary. Obviously because they were devoid of any space cues, they abandoned or suppressed a neck contribution to their 'trunk in space' perception, which, in fact, would yield an erroneous perception in almost all conditions in the dark. Both the patients and the subjects based their 'head in space' perception on their internal representation of 'trunk in space' and added to this a nuchal head-to-trunk signal. However, the patients' head-to-trunk signal, unlike that of the subjects, was considerably larger than the actual head-to-trunk rotation at low stimulus frequency. We relate this finding to some unconscious modification of their neck muscle activity during passive head rotation. It appears that the patients' gain of the neck input per se is not increased, but rather that subsets of this input are modified according to the particular function they serve.     

Contribution of self-motion perception to acoustic target localization

CONCLUSION: The findings of this study suggest that acoustic spatial perception during head movement is achieved by the vestibular system, which is responsible for the correct dynamic of acoustic target pursuit. OBJECTIVE: The ability to localize sounds in space during whole-body rotation relies on the auditory localization system, which recognizes the position of sound in a head-related frame, and on the sensory systems, namely the vestibular system, which perceive head and body movement. The aim of this study was to analyse the contribution of head motion cues to the spatial representation of acoustic targets in humans. MATERIAL AND METHODS: Healthy subjects standing on a rotating platform in the dark were asked to pursue with a laser pointer an acoustic target which was horizontally rotated while the body was kept stationary or maintained stationary while the whole body was rotated. The contribution of head motion to the spatial acoustic representation could be inferred by comparing the gains and phases of the pursuit in the two experimental conditions when the frequency was varied. RESULTS: During acoustic target rotation there was a reduction in the gain and an increase in the phase lag, while during whole-body rotations the gain tended to increase and the phase remained constant. The different contributions of the vestibular and acoustic systems were confirmed by analysing the acoustic pursuit during asymmetric body rotation. In this particular condition, in which self-motion perception gradually diminished, an increasing delay in target pursuit was observed.     

Testing otolith function.

Otolithic signals contribute to; (1) perception of orientation and linear motion, (2) generate compensatory eye movements in response to linear acceleration of the head and (3) participate in the co-ordination of movement and balance. Tests of these functions shown to be useful in identifying clinical disorders have been reviewed: (1) Evaluation of orientation to gravity, as estimated by adjustment of the visual vertical, indicates deranged otolith function at a peripheral or central level and the sensitivity of this test can be enhanced by performing estimates during centrifugation on a motorised turntable. Estimation of thresholds of self motion on a parallel swing identifies global reduction or unilateral loss of peripheral function, with central disorders awaiting study. (2) Otolith ocular reflexes to linear head translation can be used to demonstrate overall integrity of peripheral function and reveal central abnormalities. Counter-rolling responses to head roll-tilt and measurements of cyclodeviation of the eyes demonstrate functional asymmetries, with some lateralising value, particularly in central lesions. Global function and asymmetries may also be evaluated by 'head eccentric' rotational testing, which adds a tangential linear acceleration to the angular stimulus. The linear acceleration enhances the canal response by adding an otolith component. (3) Latency and amplitude of surface electro-myography (EMG) responses in the limbs to sudden falls, which can be recorded with the subject suspended on a hinged bed, indicate gross peripheral abnormality of function and can lateralize disorders of CNS motor pathways. It is concluded that some tests of otolith function can be of use in indicating global loss of peripheral otolith function, others are capable of lateralizing a marked loss of function and all have the potential to give information about central disorders. They all have to be interpreted within the clinical context and, unfortunately, none have yet been shown to be sensitive to partial, particularly unilateral, dysfunction.     

Measurement of oscillopsia induced by vestibular Coriolis stimulation

We demonstrate a new method for measuring the time constant of head-movement-contingent oscillopsia (HMCO) produced by vestibular Coriolis stimulation. Subjects briskly rotated their heads around pitch or roll axes whilst seated on a platform rotating at constant velocity. This induced a cross-coupled vestibular Coriolis illusion. Simultaneous with the head movement, a visual display consisting of either a moving field of white dots on a black background or superimposed on a subject-stationary horizon, or a complete virtual room with conventional furnishings appeared. The scene's motion was driven by a simplified computer model of the Coriolis illusion. Subjects either nulled (if visual motion was against the illusory body rotation) or matched (if motion was in the same direction as the illusory motion) the sensation with the exponentially slowing scene motion, by indicating whether its decline was too fast or too slow. The model time constant was approximated using a staircase technique. Time constants comparable to that of the Coriolis vestibular ocular reflex were obtained. Time constants could be significantly reduced by adding subject-stationary visual elements. This technique for measuring oscillopsia might be used to quantify adaptation to artificial gravity environments. In principle more complex models can be used, and applied to other types of oscillopsia such as are experienced by BPPV patients or by astronauts returning to Earth.     

The vestibular evoked response to linear, alternating, acceleration pulses without acoustic masking as a parameter of vestibular function

In this study, short latency vestibular evoked potentials (VsEPs) were recorded in five guinea pigs in response to alternating linear acceleration pulses with and without acoustic masking. A steel bolt was implanted in the skull and coupled to a shaker. Linear acceleration pulses (n = 400) in upward, downward or alternating directions were given, with a peak acceleration of 4g after 0.5 msec. Tests were repeated with acoustic masking, after modiolus destruction and after application of KCl in the vestibule. Stimuli of the vestibular nerve were recorded with a platinum electrode in the bony facial nerve canal in the bulla. Unilateral linear acceleration showed a shallow plateau at 0.5 msec, which disappeared with alternating acceleration impulses and after modiolus destruction. Therefore all further tests were done with alternating impulses. After a latency time of 0.8 msec a multiwave response was seen, with a first positive peak P1 at 1.16 ms. These were followed by other positive and negative peaks (N1, P2, N2, P3, N3). With the elimination of cochlear influences by using acoustic masking, P1 remained stable, while subsequent peaks were altered or eliminated. After modiolus destruction, the P1 peak remained, although with a smaller amplitude due to vestibular damage. After application of a saturated KCl solution in the vestibule all responses, including P1, disappeared, thus confirming the vestibular origin of these responses. We conclude that the onset latency of the VsEP and the peak latency and level of the first positive peak P1 in response to alternating linear acceleration pulses without acoustic masking, measured in the facial canal, are good and stable parameters of vestibular function in guinea pigs.     

Effect of Intranasal Treatment with Capsaicin on the Recurrence of Polyps after Polypectomy and Ethmoidectomy

In this study, short latency vestibular evoked potentials (VsEPs) were recorded in five guinea pigs in response to alternating linear acceleration pulses with and without acoustic masking. A steel bolt was implanted in the skull and coupled to a shaker. Linear acceleration pulses (n=400) in upward, downward or alternating directions were given, with a peak acceleration of 4g after 0.5 msec. Tests were repeated with acoustic masking, after modiolus destruction and after application of KCl in the vestibule. Stimuli of the vestibular nerve were recorded with a platinum electrode in the bony facial nerve canal in the bulla. Unilateral linear acceleration showed a shallow plateau at 0.5 msec, which disappeared with alternating acceleration impulses and after modiolus destruction. Therefore all further tests were done with alternating impulses. After a latency time of 0.8 msec a multiwave response was seen, with a first positive peak P1 at 1.16 ms. These were followed by other positive and negative peaks (N1, P2, N2, P3, N3). With the elimination of cochlear influences by using acoustic masking, P1 remained stable, while subsequent peaks were altered or eliminated. After modiolus destruction, the P1 peak remained, although with a smaller amplitude due to vestibular damage. After application of a saturated KCl solution in the vestibule all responses, including P1, disappeared, thus confirming the vestibular origin of these responses. We conclude that the onset latency of the VsEP and the peak latency and level of the first positive peak P1 in response to alternating linear acceleration pulses without acoustic masking, measured in the facial canal, are good and stable parameters of vestibular function in guinea pigs.