Document Detail

Effects of spatial configuration and number of fixations on Kanizsa triangle detection.
MedLine Citation:
PMID:  9375575     Owner:  NLM     Status:  MEDLINE    
PURPOSE: Illusory figures, created by the visual system between visualizing real objects, are probably caused by processes designed to segregate objects from background. Support ratio--that is, the ratio between the physically specified and total triangle side length--has been suggested to be the main spatial determinant for suprathreshold perception of a Kanizsa-type illusion. To test this scale invariance hypothesis at threshold, illusory figure perception was studied by determining the effects of inducer size and distance at various exposure durations and fixation strategies on the frequency of seeing (FoS) an illusory Kanizsa triangle. METHODS: The effect of various support ratios was studied in the first experiment by varying the intercenter distance between constant-size inducers viewed at various distances. In the second experiment, the effects of various exposure durations and fixation strategies were investigated; and the third experiment repeated the second one, with backward masking to control the processing time. In the fourth experiment, the magnification of the stimulus configuration was varied, with a support ratio that had yielded 100% FoS in the first experiment, to study the range of scale invariance in illusory figure perception. RESULTS: The support ratio was the main determinant for the perception of an illusory figure at various inducer sizes, exposure durations, and masking conditions when fixation was steady; FoS always increased from 0% to 100% with the support ratio of 0.30 to 0.37. However, free viewing, with and without masking, resulted in 100% illusory figure perception at all support ratios tested. Furthermore, when fixation was steady and support ratio and exposure duration were held constant, stimulus magnification reduced FoS from 100% to 0% at the smallest and largest stimulus sizes. CONCLUSIONS: The support ratio seems to be the main spatial determinant for illusory figure perception. However, scale invariance in Kanizsa triangle perception broke down in the smallest and largest configurations, probably because of the limitations of visual acuity and spatial integration, respectively. Integration of information from several fixations enhances FoS at small support ratios, emphasizing the importance of the binding process between separate fixations for illusory figure perception.
M Liinasuo; J Rovamo; I Kojo
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Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't    
Journal Detail:
Title:  Investigative ophthalmology & visual science     Volume:  38     ISSN:  0146-0404     ISO Abbreviation:  Invest. Ophthalmol. Vis. Sci.     Publication Date:  1997 Nov 
Date Detail:
Created Date:  1997-12-04     Completed Date:  1997-12-04     Revised Date:  2008-11-21    
Medline Journal Info:
Nlm Unique ID:  7703701     Medline TA:  Invest Ophthalmol Vis Sci     Country:  UNITED STATES    
Other Details:
Languages:  eng     Pagination:  2554-65     Citation Subset:  IM; S    
Department of Physiology, University of Helsinki, Finland.
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MeSH Terms
Fixation, Ocular / physiology*
Illusions / physiology
Sensory Thresholds
Space Perception / physiology*
Vision, Ocular / physiology

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