Document Detail

"Phase capture" in amblyopia: the influence function for sampled shape.
MedLine Citation:
PMID:  15797769     Owner:  NLM     Status:  MEDLINE    
This study was concerned with what stimulus information humans with amblyopia use to judge the shape of simple objects. We used a string of four Gabor patches to define a contour. A fifth, center patch served as the test pattern. The observers' task was to judge the location of the test pattern relative to the contour. The contour was either a straight line, or an arc with positive or negative curvature. We asked whether phase shifts in the inner or outer pairs of patches distributed along the contour influence the perceived shape. That is, we measured the phase shift influence function. Our results, consistent with previous studies, show that amblyopes are imprecise in shape discrimination, showing elevated thresholds for both lines and curves. We found that amblyopes often make much larger perceptual errors (biases) than do normal observers in the absence of phase shifts. These errors tend to be largest for curved shapes and at large separations. In normal observers, shifting the phase of inner patches of the string by 0.25 cycle results in almost complete phase capture (attraction) at the smallest separation (2 lambda), and the capture effect falls off rapidly with separation. A 0.25 cycle shift of the outer pair of patches has a much smaller effect, in the opposite direction (repulsion). While several amblyopic observers showed reduced capture by the phase of the inner patches, to our surprise, several of the amblyopes were sensitive to the phase of the outer patches. We used linear multiple regression to determine the weights of all cues to the task: the carrier phase of the inner patches, carrier phase of the outer patches and the envelope of the outer patches. Compared to normal observers, some amblyopes show a weaker influence of the phase of the inner patches, and a stronger influence of both the phase and envelope of the outer patches. We speculate that this may be a consequence of abnormal "crowding" of the inner patches by the outer ones.
Dennis M Levi; Roger W Li; Stanley A Klein
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Publication Detail:
Type:  Journal Article; Research Support, N.I.H., Extramural; Research Support, U.S. Gov't, P.H.S.    
Journal Detail:
Title:  Vision research     Volume:  45     ISSN:  0042-6989     ISO Abbreviation:  Vision Res.     Publication Date:  2005 Jun 
Date Detail:
Created Date:  2005-03-30     Completed Date:  2005-08-15     Revised Date:  2007-11-14    
Medline Journal Info:
Nlm Unique ID:  0417402     Medline TA:  Vision Res     Country:  England    
Other Details:
Languages:  eng     Pagination:  1793-805     Citation Subset:  IM    
University of California, Berkeley, School of Optometry & Helen Wills Neuroscience Institute, Berkeley, CA 94720-2020, USA.
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MeSH Terms
Amblyopia / psychology*
Discrimination (Psychology)
Form Perception*
Middle Aged
Pattern Recognition, Visual
Photic Stimulation / methods
Sensory Thresholds
Strabismus / psychology
Grant Support

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