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At least 1,207 records · Page 67Linked to original sources
PubMed1992

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.

Acceleration↗
PubMed2003

Multisensory integration in speed estimation during self-motion.

This study assessed the relative contributions of visual and proprioceptive/motor information during self-motion in a virtual environment using a speed discrimination task. Subjects wore a head-mounted display and rode a stationary bicycle along a straight path in an empty, seemingly infinite hallway with random surface texture. For each trial, subjects were required to pedal the bicycle along two paths at two different speeds (a standard speed and a comparison speed) and subsequently report whether the second speed travelled was faster than the first. The standard speed remained the same while the comparison speed was varied between trials according to the method of constant stimuli. When visual and proprioceptive/motor cues were provided separately or in combination, the speed discrimination thresholds were comparable, suggesting that either cue alone is sufficient. When the relation between visual and proprioceptive information was made inconsistent by varying optic flow gain, the resulting psychometric functions shifted along the horizontal axis (pedalling speed). The degree of separation between these functions indicated that both optic flow and proprioceptive cues contributed to speed estimation, with proprioceptive cues being dominant. These results suggest an important role for proprioceptive information in speed estimation during self-motion.

Adult↗
PubMed2005

Enhanced and diminished visuo-spatial information processing in autism depends on stimulus complexity.

Visuo-perceptual processing in autism is characterized by intact or enhanced performance on static spatial tasks and inferior performance on dynamic tasks, suggesting a deficit of dorsal visual stream processing in autism. However, previous findings by Bertone et al. indicate that neuro-integrative mechanisms used to detect complex motion, rather than motion perception per se, may be impaired in autism. We present here the first demonstration of concurrent enhanced and decreased performance in autism on the same visuo-spatial static task, wherein the only factor dichotomizing performance was the neural complexity required to discriminate grating orientation. The ability of persons with autism was found to be superior for identifying the orientation of simple, luminance-defined (or first-order) gratings but inferior for complex, texture-defined (or second-order) gratings. Using a flicker contrast sensitivity task, we demonstrated that this finding is probably not due to abnormal information processing at a sub-cortical level (magnocellular and parvocellular functioning). Together, these findings are interpreted as a clear indication of altered low-level perceptual information processing in autism, and confirm that the deficits and assets observed in autistic visual perception are contingent on the complexity of the neural network required to process a given type of visual stimulus. We suggest that atypical neural connectivity, resulting in enhanced lateral inhibition, may account for both enhanced and decreased low-level information processing in autism.

Adolescent↗
PubMed2001

Adaptation of PMLS neurons to prolonged optic flow stimuli.

Changes in neuronal responses during and after adaptation to prolonged optic flow stimulation were investigated by extracellular single-unit recording in the posteromedial lateral suprasylvian area (PMLS) of the cat. In comparison with translation stimuli, the complex optic flow patterns (radiation and rotation) produced more pronounced adaptation and after-effects by inducing larger response reduction, and altered the direction selectivity of many neurons obviously as well. Generally, the adaptation effects were direction-specific for radiation/rotation, but independent of the direction of test stimulus for translation. These results suggest that PMLS may play an important role in the perception of motion after-effects to complex optic flow fields, while the adaptation to simple translation might be generated at a relatively earlier level of the visual system.

Adaptation, Physiological↗
PubMed1999

Vestibular autonomic regulation (including motion sickness and the mechanism of vomiting).

Autonomic manifestations of vestibular dysfunction and motion sickness are well established in the clinical literature. Recent studies of 'vestibular autonomic regulation' have focused predominantly on autonomic responses to stimulation of the vestibular sense organs in the inner ear. These studies have shown that autonomic responses to vestibular stimulation are regionally selective and have defined a 'vestibulosympathetic reflex' in animal experiments. Outside the realm of experimental preparations, however, the importance of vestibular inputs in autonomic regulation is unclear because controls for secondary factors, such as affective/emotional responses and cardiovascular responses elicited by muscle contraction and regional blood pooling, have been inadequate. Anatomic and physiologic evidence of an extensive convergence of vestibular and autonomic information in the brainstem suggests though that there may be an integrated representation of gravitoinertial acceleration from vestibular, somatic, and visceral receptors for somatic and visceral motor control. In the case of vestibular dysfunction or motion sickness, the unpleasant visceral manifestations (e.g. epigastric discomfort, nausea or vomiting) may contribute to conditioned situational avoidance and the development of agoraphobia.

Agoraphobia↗
PubMed2004

The role of V5 (hMT+) in visually guided hand movements: an fMRI study.

Electrophysiological studies in animals suggest that visuomotor control of forelimb and eye movements involves reciprocal connections between several areas (striate, extrastriate, parietal, motor and premotor) related to movement performance and visuospatial coding of movement direction. The extrastriate area MT [V5 (hMT+) in humans] located in the "dorsal pathway" of the primate brain is specialized in the processing of visual motion information. The aim of our study was to investigate the functional role of V5 (hMT+) in the control of visually guided hand movements and to identify the corresponding cortex activation implicated in the visuomotor tasks using functional magnetic resonance imaging. Eight human subjects performed visually guided hand movements, either continuously tracking a horizontally moving target or performing ballistic tracking movements of a cursor to an eccentric stationary target while fixating a central fixation cross. The tracking movements were back-projected onto the screen using a cursor which was moved by an MRI-compatible joystick. Both conditions activated area V5 (hMT+), right more than left, particularly during continuous tracking. In addition, a large-scale sensorimotor circuit which included sensorimotor cortex, premotor cortex, striatum, thalamus and cerebellum as well as a number of cortical areas along the intraparietal sulcus in both hemispheres were activated. Because activity was increased in V5 (hMT+) during continuous tracking but not during ballistic tracking as compared to motion perception, it has a pivotal role during the visual control of forelimb movements as well.

Adult↗
PubMedDate not supplied

Strabismic amblyopia. Part 1. Psychophysics.

This is a two-part survey of current literature concerning strabismic amblyopia. The aim of this review is to bring the optometric practitioner up to date on the status of scientific research into strabismic amblyopia. Part 1 in this series discusses research into strabismic amblyopia from the viewpoint of psychophysical experiments that investigate both spatial and temporal behavioural deficits accompanying strabismic amblyopia. These include deficits in contrast sensitivity, spatial localisation, fixation, ocular motility, accommodation, crowding, attention, motion perception and temporal processing. Part 2 will evaluate neural processing in regard to strabismic amblyopia. It will discuss current understanding of aspects of central processing of visual information and theories regarding neural sites and mechanisms involved in amblyopia.

Journal Article↗
PubMedDate not supplied

Strabismic amblyopia. Part 2. Neural processing.

This is the second of a two-part survey of current literature concerning strabismic amblyopia. The aim of this review is to bring the optometric community up to date on the status of scientific research into strabismic amblyopia. Part 1 in this series discussed research into strabismic amblyopia from the viewpoint of psychophysical experiments, which investigate both spatial and temporal behavioural deficits accompanying strabismic amblyopia. These include deficits in contrast sensitivity, spatial localisation, fixation, ocular motility, accommodation, crowding, attention, motion perception and temporal processing. Part 2 concerns neural processing in regards to strabismic amblyopia. It discusses current understanding of more fundamental aspects of central processing of visual information and in particular current theories regarding neural sites and mechanisms involved in amblyopia.

Journal Article↗
PubMed1996

Saccades to moving targets in schizophrenia: evidence for normal posterior cortex functioning.

People diagnosed with schizophrenia have abnormalities of smooth pursuit eye movement initiation that could be attributable to dysfunction of posterior cortical areas and/or the smooth pursuit regions of frontal cortex. To evaluate whether schizophrenia patients' pursuit initiation performance is most consistent with pre- or postrolandic neuropathology, 25 schizophrenia patients and 25 nonpsychiatric individuals were presented step-ramp stimuli moving either away from or toward the fovea. Schizophrenia and nonpsychiatric individuals did not differ on position error of saccades to moving targets, suggesting that the schizophrenia patients did not have general difficulty with motion perception. During the initial 100 ms of smooth pursuit, however, schizophrenia patients had significantly slower eye velocities than did nonpsychiatric individuals. These results suggest that schizophrenia patients' smooth pursuit abnormalities are not associated with neuropathology of posterior cortical areas.

Adult↗
PubMed1985

Spatial-frequency characteristics of neurones of area 18 in the cat: dependence on the velocity of the visual stimulus.

The spatial and temporal response properties of neurones of areas 17 and 18 were studied in single units (165) of anaesthetized and paralysed cats. The visual stimuli were drifting or alternating gratings. We confirmed and extended the observation by Tolhurst & Movshon (1975) showing that the spatial-frequency characteristics of neurones of area 17 are largely independent of the temporal parameters of drifting or alternating gratings. The spatial-frequency tuning curves of neurones of area 18 shift along the spatial-frequency axis when the velocity or the temporal frequency of the drifting grating are changed. The effect of an increase either of velocity or temporal frequency is to shift the cell spatial-frequency tuning curve down the spatial-frequency scale, keeping relatively constant the strength and band width of the response. The spatial-frequency tuning curves of neurones of area 18 do not show this temporal-frequency-dependent phenomenon when the stimuli are gratings alternated in phase. In this case neurones of areas 17 and 18 show a similar behaviour. The response properties of neurones of area 18 are compared with recent psychophysical results obtained in similar experimental conditions. The hypothesis is advanced that both areas 17 and 18 are devoted to the processing of spatial information. Area 17 would be responsible for the processing of patterns in stationary or quasi-stationary situations while area 18 would be responsible for that of patterns moving at high velocities.

Animals↗
PubMed1972

Superior colliculus of the tree shrew: a structural and functional subdivision into superficial and deep layers.

Superficial lesions of the superior colliculus produced deficits in form discrimination, while deeper lesions produced, in addition, an inability to track objects. These two syndromes were related to an anatomical subdivision: Superficial lesions resulted in anterograde degeneration in the visual thalamus, whereas lesions confined to the deeper layers produced degeneration in the nonvisual thalamus and in brainstem motor areas.

Animals↗
PubMed1995

Direct perception of three-dimensional motion from patterns of visual motion.

Measurements of retinal motion along a set of predetermined orientations on the retina of a moving system give rise to global patterns. Because the form and location of these patterns depend purely on three-dimensional (3D) motion, the effects of 3D motion and scene structure on image motion can be globally separated. The patterns are founded on easily derivable image measurements that depend only on the sign of image motion and do not require information about optical flow. The computational theory presented here explains how the self-motion of a system can be estimated by locating these patterns.

Mathematics↗
PubMed1991

Sound localization by human listeners.

In keeping with our promise earlier in this review, we summarize here the process by which we believe spatial cues are used for localizing a sound source in a free-field listening situation. We believe it entails two parallel processes: 1. The azimuth of the source is determined using differences in interaural time or interaural intensity, whichever is present. Wightman and colleagues (1989) believe the low-frequency temporal information is dominant if both are present. 2. The elevation of the source is determined from spectral shape cues. The received sound spectrum, as modified by the pinna, is in effect compared with a stored set of directional transfer functions. These are actually the spectra of a nearly flat source heard at various elevations. The elevation that corresponds to the best-matching transfer function is selected as the locus of the sound. Pinnae are similar enough between people that certain general rules (e.g. Blauert's boosted bands or Butler's covert peaks) can describe this process. Head motion is probably not a critical part of the localization process, except in cases where time permits a very detailed assessment of location, in which case one tries to localize the source by turning the head toward the putative location. Sound localization is only moderately more precise when the listener points directly toward the source. The process is not analogous to localizing a visual source on the fovea of the retina. Thus, head motion provides only a moderate increase in localization accuracy. Finally, current evidence does not support the view that auditory motion perception is anything more than detection of changes in static location over time.

Attention↗