Document Detail

The role of local features in shape discrimination of contour- and surface-defined radial frequency patterns at low contrast.
MedLine Citation:
PMID:  22037304     Owner:  NLM     Status:  Publisher    
Shape processing involves a progression from a local to global analysis. A key aspect of this is the binding of distributed local features into an overall form followed by the extraction of the shape independently of its local contrast and spatial scales, so enabling the shape to be encoded based on its proportions without reference to its exact size or retinal location. Here we use contour- and surface-defined radial frequency (RF) patterns in a shape discrimination task, previously thought to reflect a global processing stage that has reached contrast and scale invariance. We compare performance across different spatial scales for a wide range of RF patterns (contour spatial frequencies of 0.7-10.0cpd, pattern radii of 0.5-10.5°), and sharp- and smooth-edged surface-RF patterns, all at low contrast (5× detection threshold). We show that shape discrimination thresholds for RF patterns have a complex series of dependencies on stimulus size (radius), contour spatial frequency (thickness), and contrast, with no scale invariance. Our results are at odds with earlier work showing no effect of radius and spatial frequency on discrimination thresholds. We show this can be accounted for by a differential effect of contrast on shape discrimination for low contrasts.
Iliya V Ivanov; Kathy T Mullen
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Publication Detail:
Type:  JOURNAL ARTICLE     Date:  2011-10-20
Journal Detail:
Title:  Vision research     Volume:  -     ISSN:  1878-5646     ISO Abbreviation:  -     Publication Date:  2011 Oct 
Date Detail:
Created Date:  2011-10-31     Completed Date:  -     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  0417402     Medline TA:  Vision Res     Country:  -    
Other Details:
Languages:  ENG     Pagination:  -     Citation Subset:  -    
Copyright Information:
Copyright © 2011 Elsevier Ltd. All rights reserved.
McGill Vision Research, Department of Ophthalmology, McGill University, 687 Pine Avenue West, H4-14, Montréal, Canada H3A 1A1.
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