Document Detail

Serial search for targets defined by divergence or deformation of optic flow.
MedLine Citation:
PMID:  1762876     Owner:  NLM     Status:  MEDLINE    
The optic flow field can be described in terms of the local differential measures, divergence, deformation, and rotation, which are informative about observer motion and the 3-D structure of the environment. Does an explicit representation of these measures exist in human visual processing in the form of a feature map? Triesman's criteria were used to investigate this; ie is there 'pop-out' for a target defined as different in local divergence or deformation from surrounding elements, or is a serial search necessary? The stimulus arrays contained 3, 5, or 9 square or rectangular elements, which each underwent repeated cycles of expansion, contraction, or deformation. The time required to detect a target undergoing the opposite transformation increased steeply with the number of elements, implying very slow serial search. (The mean time was 210 ms per element for divergence targets and 542 ms per element for deformation). The process was clearly still serial when the density and number of elements was increased up to 48 in an array 2.16 deg x 2.16 deg. In contrast, a single line element undergoing the opposite direction of translation motion to the rest of the display did show pop-out. It is concluded that no parallel processes seem to exist which are sensitive to the spatial uniformity of divergence and of deformation of optic flow. These differential properties may be derived as conjunctions of signals from a primary process which extracts local velocity. This result contrasts with our findings for targets defined by stereo disparity gradient, which show parallel processing in analogous experiments.
O J Braddick; I E Holliday
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Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't    
Journal Detail:
Title:  Perception     Volume:  20     ISSN:  0301-0066     ISO Abbreviation:  Perception     Publication Date:  1991  
Date Detail:
Created Date:  1992-02-10     Completed Date:  1992-02-10     Revised Date:  2006-11-15    
Medline Journal Info:
Nlm Unique ID:  0372307     Medline TA:  Perception     Country:  ENGLAND    
Other Details:
Languages:  eng     Pagination:  345-54     Citation Subset:  IM    
Kenneth Craik Laboratory, Department of Experimental Psychology, University of Cambridge, UK.
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MeSH Terms
Depth Perception*
Motion Perception*
Pattern Recognition, Visual*
Size Perception
Comment In:
Perception. 1993;22(4):497-500   [PMID:  8378137 ]

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