How does the human visual system compare the speeds of spatially separated objects?


No Thumbnail Available
Type
Article
Change log
Authors
Takahashi, C 
Mollon, JD 
Abstract

We measured psychophysical thresholds for discriminating the speeds of two arrays of moving dots. The arrays could be juxtaposed or could be spatially separated by up to 10 degrees of visual angle, eccentricity being held constant. We found that the precision of the judgments varied little with separation. Moreover, the function relating threshold to separation was similar whether the arrays moved in the same, in opposite or in orthogonal directions. And there was no significant difference in threshold whether the two stimuli were initially presented to the same cerebral hemisphere or to opposite ones. How are human observers able to compare stimuli that fall at well separated positions in the visual field? We consider two classes of explanation: (i) Observers' judgments might be based directly on the signals of dedicated 'comparator neurons', i.e. neurons drawing inputs of opposite sign from local regions of the visual field. (ii) Signals about local features might be transmitted to the site of comparison by a shared 'cerebral bus', where the same physical substrate carries different information from moment to moment. The minimal effects of proximity and direction (which might be expected to influence local detectors of relative motion), and the combinatorial explosion in the number of comparator neurons that would be required by (i), lead us to favor models of type (ii).

Description
Keywords
Humans, Motion Perception, Psychophysics, Space Perception, Time Factors, Visual Perception
Journal Title
PLoS One
Conference Name
Journal ISSN
1932-6203
1932-6203
Volume Title
15
Publisher
Public Library of Science (PLoS)
Rights
All rights reserved
Sponsorship
Biotechnology and Biological Sciences Research Council (BB/S000623/1)
Marina