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| Research article summary (published 30 May 2003): |
Dual nonlinearities regulate contrast sensitivity in pattern discrimination tasks.
Full Abstract
Many current psychophysical models propose that visual processing in cortex is hierarchical, with nonlinearities sandwiched between linear stages of processing. In earlier publications, we proposed a model of this type to account for masking effects found with spatial frequency and orientation discriminations. Our model includes two nonlinear mechanisms that regulate contrast sensitivity in early cortical mechanisms. The first is a local within-pathway nonlinearity that accelerates at low contrasts but is compressive at high. The second is a pooled nonlinear gain control process that operates over a broad range of neurons with different tuning characteristics. Here, we test predictions of the model for spatial frequency discriminations. The model predicts that at low contrasts, adding a grating mask oriented parallel to test gratings will improve discrimination performance via operation of the within-pathway nonlinearity, analogous to the "dipper effect" found with contrast discriminations. Adding an orthogonally oriented mask is predicted to have no effect at low contrasts, where pooled gain control processes contribute little to performance. At high contrasts, the model predicts that performance will asymptote and become independent of contrast with either parallel or orthogonal masks. The results confirm model predictions.
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Author information
Author/s: Olzak, Lynn A (LA); Thomas, James P (JP);
Affiliation: Department of Psychology, Miami University of Ohio, Oxford, OH 45056, USA. olzakla(-atsign-)muohio.edu
Grants: EY00360 (Agency:United States NEI) ; EY13953 (Agency:United States NEI)
Journal and publication information
Publication Type: Journal Article; Research Support, U.S. Gov't, P.H.S.
Journal: Vision research (Vision Res), published in England. (Language: eng)
Reference: 2003-Jun; vol 43 (issue 13) : pp 1433-42
Dates: Created 2003/05/27; Completed 2003/08/12; Revised 2007/11/14;
PMID: 12767311, status: MEDLINE (last retrieval date: 11/6/2008)
Sourced from the National Library of Medicine. Abstract text and other information may be subject to copyright.
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