Transparency and coherence in human motion perception

Article Abstract:

The visual system performs many complex tasks; one is the accurate detection of moving objects. There are two components of motion to which the visual system appears to respond: pattern motion and component motion. If two gratings of striped parallel lines at right angles to one another are moved so that one lies on top of the other, there is a point where the observer identifies a coherent, plaid pattern moving straight ahead (pattern motion) rather than the individual, different, components moving at right angles to each other (component motion). Since the direction of movement for the pattern is different from that of either component, it seems that the visual system computes the direction in which the pattern moves. To test whether transparency has a role in motion perception, subjects were shown gratings whose intersections had varying luminance (brightness). The stimuli were moved and subjects reported whether they saw pattern motion. Results demonstrate that the tendency to see component motion depends on whether the gratings look transparent. If luminance is adjusted so that the two gratings do not look as if they are transparent, subjects are more likely to report component motion. The findings suggest that transparency is an important aspect of scenes; consideration of this variable should be included in the designs of visual experiments. (Consumer Summary produced by Reliance Medical Information, Inc.)

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Attentional modulation of visual motion processing in cortical areas MT and MST

Article Abstract:

The responses of direction-specific neurons in the visual cortex of monkeys is significantly affected by attention in the middle temporal visual (MT) and medial superior temporal (MST) areas. The extraretinal effects increase with levels of cortical processing, from sensory representations in the initial stages of retinocortical pathway to representations in later extrastriate cortex. The results of the study show that the responses of extrastriate cortex neurons are affected by the behavioral state of the organism rather than merely the sensory features of the visual input.

Physiological aspects, Observations, Cerebral cortex, Anatomy, Attention (Psychology), Monkeys as laboratory animals, Laboratory monkeys, Attention

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Denial of disabilities in anosognosia

Article Abstract:

Some patients with right-hemisphere stroke and left-sided hemiplegia deny not only their own, but also another patient's, paralysis. These patients can perform instructed skilled movements with their right hands. They fail to show any left parietal or frontal lesions which may account for this denial. This indicates that the denial is not due to body-part confusion.

Psychological aspects, Reports, Denial (Psychology), Hemiplegia, Anosognosia

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