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Information specifying the future passing distance of an approaching object is available (in units of object size) in the ratio of optical displacement velocity and optical expansion velocity. Despite empirical support for the assumption that object size can serve as a metric in the perception of passing distance, the present series of experiments reveals(More)
The perceived direction of a grating moving behind an elongated aperture is biased towards the aperture's long axis. This "barber pole" illusion is a consequence of integrating one-dimensional (1D) or grating and two-dimensional (2D) or terminator motion signals. In humans, we recorded the ocular following responses to this stimulus. Tracking was always(More)
We investigated the effects of stationary and moving textured backgrounds on ocular and manual pursuit of a discrete target that suddenly starts to move at constant speed (ramp motion). When a stationary textured background was superimposed to the target displacement, the gain of the steady-state eye smooth pursuit velocity was significantly reduced, while(More)
We present the first assessment of motion vision in childhood autism. Postural reactivity to visually perceived motion was measured in five autistic children and 12 normal controls of the same chronological age. Anteroposterior as well as total body sway occurring on a force platform in response to movements in the visual environment were compared. Autistic(More)
Motion transparency requires that the visual system distinguish different motion vectors and selectively integrate similar motion vectors over space into the perception of multiple surfaces moving through or over each other. Using large-field (7 degrees x 7 degrees) displays containing two populations of random-dots moving in the same (horizontal) direction(More)
Observers viewed random-dot optical flow displays that simulated self-motion on a circular path and judged whether they would pass to the right or left of a target at 16 m. Two dots in two frames are theoretically sufficient to specify circular heading if the orientation of the rotation axis is known. Heading accuracies were better than 1.5 degrees with a(More)
The aim of the present study was to search for a sensorimotor marker (i.e., visuopostural tuning) that could be correlated with the severity of motor impairments in children with autistic spectrum disorders. Given that autistic children were previously reported to be posturally hyporeactive to visually perceived environmental motion in comparison with(More)
We measured spatiotemporal contrast sensitivity and gait variables in a 60-year-old man who had spontaneous episodes of freezing gait without any sign of rigidity or tremor. One major factor triggering freezing was the characteristics of visual space, as freezing episodes occurred during spontaneous walking and passing through apertures and never during(More)
Motion perception was studied in a subject with bilateral lesion of the visual cortex, involving severe damage to cortical areas V1 and V4, but with no apparent damage to visual associative areas situated in occipito-parietal and lateral occipito-temporal (presumably V5) zones. He was able to perceive optical flow motions simulating motion in depth in(More)