Visual motion stimulation,but not visually induced perception of self-motion,biases the perceived direction of verticality

Large-field torsional optokinetic stimulation is known to affect the perceived direction of gravity with verticality judgements deviating towards the direction of visual stimulus rotation. The present study aimed to replicate this effect and to examine it further by subjecting participants to optokinetic stimulation in roll, resulting in spontaneous alternations between the perception of object-motion and that of contradirectional self-motion (vection), as reported by the subjects. Simultaneously, subjects were oscillated laterally in a flight simulator and indicated their perception of postural verticality. Results confirmed that rotation of the visual environment in the frontal plane biases the perceived orientation of gravity towards the direction of visual stimulus motion. However, no differential effect of perceptual state on postural verticality was obtained when contrasting verticality judgements made during the perception of object-motion with those obtained during reported self-motion perception. This finding is likely to reflect a functional segregation of central nervous visual-vestibular subsystems that process the perception of self-tilt and that of self-rotation to some degree independently.     

Cortical responses to object-motion and visually-induced self-motion perception

We investigated the spatiotemporal cortical dynamics during the perception of object-motion and visually-induced self-motion perception in six normal subjects, using a 143-channel neuromagnetometer. Object-motion specific tasks evoked early transient activity over the right temporooccipital cortex, while self-motion perception, or vection, additionally was followed by sustained bilateral activity in the temporoparietal area. The specific signal distributions suggest to represent the different perceptual modes of object-motion and self-motion sensation.     

Processing of visual motion direction in the fronto-parallel plane in the stationary or moving observer

To examine the effect of concurrent self-motion on the perception of the direction of object-motion, random-dot kinematograms were employed in which the strength of the directional signal was manipulated by varying the percentage of coherently moving pixels. The subject's task was to indicate the motion direction of briefly presented displays while undergoing whole body rotations with angular accelerations of 0, 5, 15, or 45°/s². The perception of the direction of visual motion in the horizontal plane was impaired only when visual and vestibular motion directions were incongruous. The impairment increases with both increasing angular acceleration and decreasing percentage of coherently moving pixels. For object-motion in the vertical plane, an impairment was found for both congruous and incongruous combination of visual and vestibular stimulation, although not as pronounced for the latter (i.e., visual upward, vestibular downward stimulation, and vice versa). These results are discussed in terms of postnatal development and neurophysiological optimization processes resulting from intersensory ‘updating’ through every-day experience of object-motion during self-motion.     

Object-motion detection affected by concurrent self-motion perception: psychophysics of a new phenomenon

Thresholds for object-motion detection are significantly raised when concurrent self-motion perception is induced by either vestibular, or visual, or cervico-somatosensory stimulation. Active sinusoidal horizontal head oscillations with compensatory vestibulo-ocular reflex (VOR) and foveal or eccentrical target presentation; 'passive' head movements with fixation suppression of the VOR; pure body oscillations with the head fixed in space (cervical stimulation); optokinetically induced apparent self-motion (circularvection). This new visual phenomenon of a physiological 'inhibitory interaction' between object- and self-motion perception seems to have a somatosensory motor analogue. It may reflect the disadventageous side effect due to unspecificness of an otherwise beneficial space constancy mechanism, which provides us with the image of a stable world during locomotion.     

Simple method of differential diagnosis of peripheral and central vertigo--development of diagnostic method and studies of 178 cases]

In patients who complain of vertigo or who have equilibrium disorders, it is often difficult to determine the etiology of the disorder, that is to determine whether it is dependent on a peripheral or central vestibular disorder. To attempt to determine the etiology in these cases, we divised a new method, the caloric eye tracking pattern test (CETP-Test). Seventeen normal subjects and 161 patients were tested. The latter group included 33 with peripheral disorders such as Meniere's disease, benign paroxysmal positional nystagmus, and others, and 128 with central disorders such as vertebral basilar artery insufficiency, cervical vertigo, and others, were tested. The cases of central disorders were limited to those patients whose eye tracking pattern before the caloric stimulation was normal. In normal subjects and in patients with peripheral disorders, it is well known that caloric nystagmus has little influence on the eye tracking pattern. In contrast, in patients with central vestibular disorders, caloric nystagmus evokes abnormalities on the eye tracking pattern, either superimposed or saccades, despite the fact that the eye tracking pattern before the caloric stimulation is normal. First we administer the eye tracking stimulation test using a target which moves horizontally at 0.3 cycle per second. Next, we perform the caloric test on the right ear, using 20 c.c. of ice water for 10 seconds. During the evoked caloric nystagmus we administer the eye tracking test once again. The eye tracking pattern is recorded for 20 seconds beginning 50 seconds after the start of the ice water injection. The procedure repeated on the left ear. The results on each case are presented as three patterns of ENG-recording. We may stat that in normal subjects and in patients with peripheral vestibular disorders, visual suppression of caloric nystagmus remains functional. Caloric induced nystagmus does not affect the CETP. In patients with central vestibular disorders, visual suppression of caloric nystagmus does not function properly because of defects in the visual suppression mechanism. Therefore, caloric nystagmus greatly influences the CETP. Consequently, the CETP may not be smooth when CETP test is administered to patients with central vestibular disorders. We may say also that the visual suppression to the vestibular nystagmus is evoked more strongly by pursuing a moving visual stimulus than by gazing a stational target. These results allow for a differential diagnosis between peripheral and central disorders.     

Expectation and the vestibular control of balance

Recent experiments have shown that the visual channel of balance control is susceptible to cognitive influence. When a subject is aware that an upcoming visual disturbance is likely to arise from an external agent, that is, movement of the visual environment, rather than from self-motion, the whole-body response is suppressed. Here we ask whether this is a principle that generalizes to the vestibular channel of balance control. We studied the whole-body response to a pure vestibular perturbation produced by galvanic vestibular stimulation (GVS; 0.5 mA for 3 sec). In the first experiment, subjects stood with vision occluded while stimuli were delivered either by the subject himself (self-triggered) or by the experimenter. For the latter, the stimulus was delivered either without warning (unpredictable) or at a fixed interval following an auditory cue (predictable). Results showed that GVS evoked a whole-body response that was not affected by whether the stimulus was self-triggered, predictable, or unpredictable. The same results were obtained in a second experiment in which subjects had access to visual information during vestibular stimulation. We conclude that the vestibular-evoked balance response is automatic and immune to knowledge of the source of the perturbation and its timing. We suggest the reason for this difference between visual and vestibular channels stems from a difference in their natural abilities to signal self-motion. The vestibular system responds to acceleration of the head in space and therefore always signals self-motion. Visual f low, on the other hand, is ambiguous in that it signals object motion and eye motion, as well as self-motion.     

Detection thresholds for object motion and self-motion during vestibular and visuo-oculomotor stimulation

We compared the detection threshold for object motion with that of self-motion in space in healthy human subjects. Stimuli consisted of horizontal rotations of subjects' body with a fixation spot kept in fixed alignment with their heads (vestibular stimulus), rotation of the fixation spot relative to the stationary subjects (visuo-oculomotor stimulus), and a combination thereof by applying rotations of subjects' body relative to the stationary object (sinusoidal oscillations, 0.025–0.4 Hz). Two series of experiments were performed. 1) One group of subjects was instructed to attend to, and to indicate the occurrence of, either object or self-motion. 2) A second group was instructed not only to detect the occurrence of a perception, but also to qualify it either as object motion or self-motion, depending on which modality dominated perceptually. With either instruction it was found that all three stimulus conditions could evoke both, either an object motion perception or a self-motion perception. The detection thresholds of both perceptions were essentially similar. Thresholds were highest with the vestibular stimulus, intermediate with the stimulus combination, and lowest with the visuo-oculomotor stimulus. The vestibular threshold depended on stimulus frequency, in that it decreased with increasing frequency. Thereby, it became similar to the visuo-oculomotor one, which was essentially constant across frequency. Probability of occurrence of the perceptions in the first experimental series was considerably higher than in the second series, suggesting an important role of attentional mechanisms. In the second series, percent frequency of occurrence of veridical perception (object motion with visuo-oculomotor stimulus, self-motion with stimulus combination) was at chance level (50%) at low stimulus frequency, but was augmented considerably at high frequency. We assume that the latter effect is brought about by a visual-vestibular conflict measure by which the visual stimulus (light spot) is qualified as representing either a moving object or a spatial reference for self-motion. While at suprathreshold stimulus intensities the conflict can determine perception magnitude, at threshold levels its influence is restricted mainly on the probability of occurrence of object and self-motion perception.     

Visually evoked eye movements: Effects of labyrinthectomy

Nystagmus responses of cats to both optokinetic and flicker stimuli were studied before and after unilateral and bilateral labyrinthectomy. Destruction of the labyrinths served to reduce significantly the number of eye movements to each type of the visual stimuli. The opposite-direction after-nystagmus elicited by the optokinetic stimulus were abolished by bilateral labyrinthectomy. No changes occurred in the frequency of the flash nystagmus response that could be ascribed to body position. Thus, the data confirm previous work by others, but suggest species differences with regard to several properties of visually evoked nystagmus.     

Influence of long-term optokinetic stimulation on eye movements of the rabbit

Two kinds of optokinetic afternystagmus (OKAN) have been studied in rabbits; positive and negative OKAN. Positive OKAN is the persistence of eye movements evoked by optokinetic stimulation following the termination of the stimulus, with the slow phase of the eye movements in the same direction as the inducing stimulus. Negative OKAN is evoked by long duration optokinetic stimulation, and has a slow phase of opposite direction to the inducing stimulus. The stimulus conditions which are optimal for inducing and maintaining negative OKAN were characterized. Rabbits were placed in an optokinetic drum for periods of 12-96 h (with appropriate intervening periods for food and water). Eye movements were recorded during and after the termination of optokinetic stimulation. The optimum optokinetic stimulus velocity for the induction of negative OKAN was 5 degrees/s. The minimum duration of stimulation for the induction of negative OKAN of maximum velocity was 48 h. Once induced, the slow phase of negative OKAN attained velocities of 50-100 degrees/s. Three conditions of restraint of the rabbits were studied after negative OKAN was induced during the intervening periods when eye movements were not being recorded. These conditions were: (1) unrestrained (full freedom of movement) without visual stimulation (in a dark enclosure); (2) restrained (horizontal head and body movement prevented) without visual stimulation; and (3) restrained with visual stimulation (in the stationary optokinetic drum). Conditions 1 and 2 caused negative OKAN to dissipate within 24 h. Condition 3 caused negative OKAN to be maintained for more than 70 h. The velocity imbalance of the horizontal vestibuloocular reflex (HVOR) was measured at different times following the induction of negative OKAN. It provided a more sensitive index of the central imbalance which caused negative OKAN, than did spontaneous nystagmus. One of the consequences of optokinetic stimulation measured over a 16 h period was a decrease in the gain of the optokinetic reflex. This reduction in gain could represent a central adaptation to maintained stimulation which in the absence of continued optokinetic stimulation is expressed as a nystagmus.     

Interaction of linear vestibular and visual stimulation in the macaque ventral intraparietal area (VIP)

Navigation in space requires the brain to combine information arising from different sensory modalities with the appropriate motor commands. Sensory information about self-motion in particular is provided by the visual and the vestibular system. The macaque ventral intraparietal area (VIP) has recently been shown to be involved in the processing of self-motion information provided by optical flow, to contain multimodal neurons and to receive input from areas involved in the analysis of vestibular information. By studying responses to linear vestibular, visual and bimodal stimulation we aimed at gaining more insight into the mechanisms involved in multimodal integration and self-motion processing. A large proportion of cells (77%) revealed a significant response to passive linear translation of the monkey. Of these cells, 59% encoded information about the direction of self-motion. The phase relationship between vestibular stimulation and neuronal responses covered a broad spectrum, demonstrating the complexity of the spatio-temporal pattern of vestibular information encoded by neurons in area VIP. For 53% of the direction-selective neurons the preferred directions for stimuli of both modalities were the same; they were opposite for the remaining 47% of the neurons. During bimodal stimulation the responses of neurons with opposite direction selectivity in the two modalities were determined either by the visual (53%) or the vestibular (47%) modality. These heterogeneous responses to unimodal and bimodal stimulation might be used to prevent misjudgements about self- and/or object-motion, which could be caused by relying on information of one sensory modality alone.     

Discharges of Purkinje cells in monkey's flocculus during smooth-pursuit eye movements and visual stimulus movements

Modulations in discharges of Purkinje cells (P cells) associated with movements of visual patterns were studied in the flocculus of monkeys trained to execute smooth-pursuit eye movements and to suppress optokinetic nystagmus. One class of P cells responded to the movements of visual stimulus regardless of whether the eyes remained stationary (produced retinal-slip velocity) or moved with the stimulus produced eye velocity). These P cells processed high-order information concerning the absolute velocity of stimulus movements and thereby the eye velocity had already been incorporated in the visual responses (visuomotor P cells). The other class of P cells responded to visual inputs resulting from the retinal slip (visual P cells). The majority of visual P cells (82%) also modulated their activities during smooth pursuit. When sinusoidal trackings were executed against a stationary visual background, various types of interactions occurred in the P-cell responses between the converging visual and oculomotor inputs. The type of interaction was related to the preferred direction for the P cell during eye movements and the side of the peripheral receptive field.     

Simulated nystagmus suppresses pattern-reversal but not pattern-onset visual evoked potentials.

OBJECTIVE: The aim of this study is to quantify and compare the effects of simulated horizontal nystagmus on pattern-reversal and pattern-onset visual evoked potentials (VEPs). METHODS: In eight visually normal subjects with normal oculomotor behaviour, we monitored eye movements and recorded pattern-reversal and pattern-onset VEPs from occipital electrodes. Subjects viewed the stimulus monocularly via a mirror, which was placed close to the eye and driven by a scanner at four different amplitudes (0, 1, 2, and 3 degrees ) with a 4 Hz saw-tooth waveform to simulate horizontal jerk-nystagmus. RESULTS: Retinal image motion nearly abolished the pattern-reversal VEPs (maximal reduction by 85%; mean reduction by 72%, P<0.001), while there was a non-significant reduction (mean reduction by 15%) of the pattern-onset VEPs. CONCLUSIONS: The differential effect of simulated nystagmus on pattern-reversal and pattern-onset VEPs resembles that reported in studies on nystagmus patients. We conclude that the interaction of retinal image motion with the stimulus is sufficient to explain the reduction of pattern-reversal VEPs in patients with nystagmus and propose simulated nystagmus as a useful tool to test the influence of nystagmus on the efficiency of VEP stimuli. SIGNIFICANCE: This study demonstrates how horizontal jerk-nystagmus can be simulated and suggests possible mechanisms by which nystagmus reduces VEP responses.     

Human DC scalp potentials during vestibular and optokinetic stimulation: non-specific responses?

In normal subjects transient horizontal body rotation in the dark (vestibular stimulation) elicited a DC potential change with the maximum at Cz. The response appeared to covary with stimulus velocity, which is the most relevant stimulus parameter transferred by the horizontal semicircular canal system. A similar response was obtained during optokinetic stimulation. However, the following findings suggested that the responses are related to 'high' perceptual functions rather than representing a visuo-vestibular evoked cortical potential: (a) the visual response was found independent of whether the subjects perceived, as a task, self-motion in a stationary environment or 'object' motion about the stationary body; its amplitude depended on the subjects' subjective compliance to the task; (b) when presenting various combinations of optokinetic and vestibular stimuli, the response amplitude depended on the subjective and objective intersensory conflict in the combinations; (c) sinusoidal stimulation yielded a negative shift of the DC potential, but the potential was not modulated along with the waxing and waning of stimulus velocity or of the self-motion sensation evoked; (d) patients with loss of vestibular functions showed a similar Cz response during body rotation in the dark.     

Physiology of perception: cortical stimulation and recording in humans

OBJECTIVES: 1) To determine the effect of stimulus train duration (TD) on sensory perception using direct stimulation of somatosensory and visual cortices. 2) To investigate the occurrence of evoked potentials in response to stimulation that is subthreshold for perception. BACKGROUND: Studies of the mechanisms of conscious perception using direct cortical stimulation and recording techniques are rare. The clinical necessity to implant subdural electrode grids in epilepsy patients undergoing evaluation for surgery offers an opportunity to examine the role of stimulus parameters and evoked potentials in conscious perception. METHODS: Subjects included epilepsy patients with grids over somatosensory or occipital cortex. Single pulses (100 microseconds) and stimulus trains were applied to electrodes, and thresholds for perception were found. Evoked potentials were recorded in response to peripheral stimulation at intensities at, above, and below sensory threshold. RESULTS: During cortical stimulation, sensory threshold changed little for stimulus trains of 250 milliseconds and longer, but increased sharply as TD decreased below this level. Primary evoked activity was recorded in response to peripheral stimulations that were subthreshold for conscious perception. CONCLUSIONS: The results confirm a previous report of the effects of stimulus TD on sensory threshold. However, no motor responses occurred following somatosensory stimulation with short trains, as previously reported. The TD threshold pattern was similar in visual cortex. In agreement with the previous report, early components of the primary evoked response were not correlated with conscious sensory awareness.     

Vestibulo-ocular reflex (VOR), cervico-ocular reflex (COR) and its interaction in active head movements

In normal adults the vestibulo-ocular reflex (VOR) and the cervico-ocular reflex (COR) were investigated during passive and active head or body movements, respectively. Sinusoidal rotations around the vertical axis of the body at frequencies of 0.05, 0.1, and 0.2s-1 and total amplitudes of 20 degrees, 40 degrees, 60 degrees, or 80 degrees were employed. The average eye deviations (Schlagfeld) during VOR were directed opposite to the direction of the head turning. During COR, however, slow eye deviations of higher amplitude were anticompensatory relative to the fixed head. During active head turnings the average eye deviations showed the same anticompensatory direction as in COR, but were still larger. The increased with stimulus amplitudes up to 60 degrees. At least a weak cervical nystagmus was elicited in all subjects, with its fast phases beating in the direction of the relative head movement. Its gain reached marked values up to 0.5, but only for peak stimulus velocities below 25%. The nystagmus gain during active head turnings was only slightly higher than during VOR. With higher stimulus velocities, large anticompensatory saccades appeared just before the change of stimulus direction; these are typical for active head movements, but were also found during COR.     

Electrophysiological correlates of optokinetic and reversed postoptokinetic nystagmus in the rabbit.

Six rabbits with implanted electrodes in visual cortex, lateral geniculate body, superior colliculus and the mesodiencephalic nystagmogenic centres were exposed to 90 min optokinetic stimulation, followed by 30 to 60 min observation of reversed postoptokinetic nystagmus (RPN) in darkness. The oculographically recorded nystagmus was used to trigger a LINC 8 computer programmed for perisaccadic EEG averaging and for examination of excitability of visual centres by flashes applied at different intervals after the saccade onset. Whereas optokinetic nystagmus (OKN) was accompanied by marked electrical potentials appearing at all recording sites during and for about 100 msec after the saccade, these potentials were considerably attenuated or absent during RPN. Visual evoked responses to flashes applied during the OKN saccades were considerably smaller than responses to flashes delayed by 130-200 msec. No saccadic suppression was observed when the same visual stimuli were applied during RPN saccades in darkness. It is concluded that eye movements generated in the absence of external stimuli during RPN elicit only weak corollary discharge.     

Improvement in evoked vestibular responses by tubular vision

Numerous factors can influence evoked or spontaneous nystagmus. In this study, the influence of reducing the visual field to a peripheral field of 18 degrees 40' was investigated in 15 subjects with normal vision. In order to reproduce the conditions of photoelectric recording with Torok's glasses, a tube was placed in front of one eye while the other eye was covered. This resulted in the enhancement of the evoked vestibular and optovestibular responses and the reduction of the subjective sensations of the subject, suggesting that the tubular vision might be helpful for the study of cinetosis. Our study also showed two culminating points and two critical phases in caloric nystagmus.     

Role of the nucleus reticularis tegmenti pontis on visually induced eye movements

Optokinetic nystagmus (OKN) and visual suppression of caloric nystagmus were tested in cats with electrolytic lesions in the nucleus reticularis tegmenti pontis (NRT) or with hemicerebellectomies. The animals with a NRT lesion could follow higher stimulus velocities, but the eye movement output saturated at 10°/s. In the hemicerebellectomized cats, on the other hand, slow-phase OKN velocity was normal at stimulus velocities less than 30°/s. In addition, OKN impairment was more transient in the cats with hemicerebellectomies than in those with NRT lesions. In the cats with a NRT lesion, loss of visual suppression of caloric nystagmus was apparent in nystagmus with the slow phase toward the lesion side, whereas in cats with hemicerebellectomies, it was toward the contralateral side to the lesion. These findings suggest that the NRT may be a part of the relay nuclei mediating optokinetic signals responsible for OKN at all optokinetic stimulus velocities and the flocculus may be responsible for OKN at higher optokinetic stimulus velocities. In addition, the NRT may also be one of the prefloccular nuclei conveying visual input signals responsible for visual suppression of caloric nystagmus to the contralateral flocculus.     

Vestibulo-ocular reflex (VOR), cervico-ocular reflex (COR) and its interaction in active head movements

Summary In normal adults the vestibulo-ocular reflex (VOR) and the cervico-ocular reflex (COR) were investigated during passive and active head or body movements, respectively. Sinusoidal rotations around the vertical axis of the body at frequencies of 0.05, 0.1, and 0.2 s^–1 and total amplitudes of 20°, 40°, 60°, or 80° were employed.The average eye deviations (Schlagfeld) during VOR were directed opposite to the direction of the head turning. During COR, however, slow eye deviations of higher amplitude were anticompensatory relative to the fixed head. During active head turnings the average eye deviations showed the same anticompensatory direction as in COR, but were still larger. They increased with stimulus amplitudes up to 60°.At least a weak cervical nystagmus was elicited in all subjects, with its fast phases beating in the direction of the relative head movement. Its gain reached marked values up to 0.5, but only for peak stimulus velocities below 25°/s. The nystagmus gain during active head turnings was only slightly higher than during VOR.With higher stimulus velocities, large anticompensatory saccades appeared just before the change of stimulus direction; these are typical for active head movements, but were also found during COR.Supported by Sonderforschungsbereich Hirnforschung und Sinnesphysiologie (SFB 70) der Deutschen Forschungsgemeinschaft (DFG)     

Muscarinic antagonists in the treatment of acquired pendular and downbeat nystagmus: A double-blind,randomized trial of three intravenous drugs

We performed a double-blind, randomized trial of intravenous scopolamine, benztropine, and glycopyrrolate in 7 patients with acquired nystagmus and oscillopsia. Five patients had pendular nystagmus and 2, downbeat nystagmus. We recorded eye movements with a magnetic search coil technique and tested visual acuity and motion perception before and after administration of each drug. Scopolamine reduced nystagmus in all patients. Benztropine was moderately effective and glycopyrrolate had a negligible impact. Visual acuity improved only with scopolamine; motion discrimination and oscillopsia improved significantly with scopolamine and benztropine. Pendular and downbeat nystagmus respond to intravenous antagonists of central muscarinic receptors.