| Shape discrimination for motion-defined and contrast-defined form: squareness in special. | |
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MedLine Citation:
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PMID: 1762874 Owner: NLM Status: MEDLINE |
Abstract/OtherAbstract:
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Shape discrimination was measured for: (i) two-dimensional rectangular targets that were perfectly camouflaged within a stationary pattern of random dots and rendered visible by relative motion of the dots, and (ii) similar dotted rectangles that were rendered visible by luminance contrast. Shape discrimination was disconfounded from size discrimination by requiring subjects to discriminate the aspect ratios of rectangles whose areas were altered independently of aspect ratio. When dot speed and contrast were both high, the aspect-ratio discrimination threshold was as acute for motion-defined (MD) rectangles as for contrast-defined (CD) rectangles and, at 2-3%, corresponded to a change of side length of about 24 s arc compared to a mean dot separation of 360 s arc. Discrimination of MD rectangles collapsed at low dot speeds and could not be measured at speeds less than about 0.03-0.08 deg s-1, but discrimination of CD rectangles was almost unaffected by dot speed. The aspect-ratio discrimination threshold was lowest for a square and progressively increased as the rectangle became more asymmetric. It is suggested that the visual system contains a mechanism that compares the separations of pairs of contours along different azimuths, and that, during visual development, this shape-discrimination processing of MD and CD targets is driven by the same environmental and behavioural pressures towards a common end point. The human equivalent of a pathway that includes the cortical area MT is thought to be important for shape discrimination of MD forms. |
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Authors:
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D Regan; S Hamstra |
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Publication Detail:
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Type: Journal Article; Research Support, Non-U.S. Gov't |
Journal Detail:
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Title: Perception Volume: 20 ISSN: 0301-0066 ISO Abbreviation: Perception Publication Date: 1991 |
Date Detail:
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Created Date: 1992-02-10 Completed Date: 1992-02-10 Revised Date: 2006-11-15 |
Medline Journal Info:
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Nlm Unique ID: 0372307 Medline TA: Perception Country: ENGLAND |
Other Details:
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Languages: eng Pagination: 315-36 Citation Subset: IM |
Affiliation:
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Department of Psychology, York University, Ontario, Canada. |
Export Citation:
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APA/MLA Format Download EndNote Download BibTex |
| MeSH Terms | |
Descriptor/Qualifier:
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Attention* Discrimination Learning* Field Dependence-Independence Form Perception* Humans Motion Perception* Orientation Psychophysics Sensory Thresholds |
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine
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