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Results for “Visual Perception”

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At least 721 records · Page 40Linked to original sources
PubMed1976

A possible means of monitoring the progress of demyelination in multiple sclerosis: effect of body temperature on visual perception of double light flashes.

The ability to discriminate closely separated pairs of light flashes as being double is impaired in multiple sclerosis. The effects of altering body temperature on double flash resolution and on visual acuity were studied in four multiple sclerosis patients and in control subjects. At demyelinated sites heating impaired and cooling improved double flash resolution. Visual acuity behaved similarly. The double flash test was very sensitive, changing up to 75 ms in response to simple heating and cooling procedures that produced small variations in acuity. Apart from its diagnostic value, the double flash test furnishes a simple in vivo model to study the effect of temperature change (and potential symptomatic therapy) on conduction in partially demyelinated axons in the visual system.

Adult↗
PubMed2002

Colour and luminance interactions in the visual perception of motion.

We sought to determine the extent to which red-green, colour-opponent mechanisms in the human visual system play a role in the perception of drifting luminance-modulated targets. Contrast sensitivity for the directional discrimination of drifting luminance-modulated (yellow-black) test sinusoids was measured following adaptation to isoluminant red-green sinusoids drifting in either the same or opposite direction. When the test and adapt stimuli drifted in the same direction, large sensitivity losses were evident at all test temporal frequencies employed (1-16 Hz). The magnitude of the loss was independent of temporal frequency. When adapt and test stimuli drifted in opposing directions, large sensitivity losses were evident at lower temporal frequencies (1-4 Hz) and declined with increasing temporal frequency. Control studies showed that this temporal-frequency-dependent effect could not reflect the activity of achromatic units. Our results provide evidence that chromatic mechanisms contribute to the perception of luminance-modulated motion targets drifting at speeds of up to at least 32 degrees s(-1). We argue that such mechanisms most probably lie within a parvocellular-dominated cortical visual pathway, sensitive to both chromatic and luminance modulation, but only weakly selective for the direction of stimulus motion.

Adaptation, Ocular↗
PubMed2006

An MEG study into the visual perception of apparent motion in depth.

This study investigated (1) the responses associated with the perception of motion in depth induced by a series of scale-changing paradigms, and (2) the locations of the dipoles in the brain elicited by stimuli of motion in depth and in-plane motion. The former was determined using two types of stimulation: real motion and apparent motion in scale (AMS; where two frames with size-changed patterns were presented alternately); and the latter was determined by moving a full-field checkerboard pattern forward or rightward smoothly with the same time course. The results from analyzing magnetoencephalography (MEG) component M160 to differentiate the signals of perception can be summarized as follows: (1) the neurons stimulated by apparent motion (AM) might be similar to those stimulated by a real motion, since there was no statistical difference associated with the signals at M160 and the dipole locations; (2) the perceptional signal of motion in depth seems to be more sensitive when scale-changing information is present; and (3) asymmetrical responses are present in the visual system, with responses being more sensitive to expanding stimuli than to contracting ones, and with the activity being more prominent in the right occipitotemporal area. Overall, this study indicates that the responses evoked by the stimuli causing motion in depth are allocated more to area V3a rather to area V5.

Adult↗