Document Detail

Apparent contrast differs across the vertical meridian: visual and attentional factors.
MedLine Citation:
PMID:  18318619     Owner:  NLM     Status:  MEDLINE    
It is known that visual performance is better on the horizontal than the vertical meridian, and in the lower than the upper region of the vertical meridian (Vertical Meridian Asymmetry, "VMA"), and that exogenous spatial attention increases the apparent contrast of a stimulus. Here we investigate whether the VMA also leads to differences in the subjective appearance of contrast between the upper and lower vertical meridian, and how the effects of exogenous spatial attention on appearance interact with the VMA. Two Gabor stimuli were presented North and South of fixation at 4 degrees eccentricity along the vertical meridian. Observers were asked to report the orientation of the Gabor that was higher in contrast. By assessing which stimulus observers perceived to be higher in contrast, we obtained psychometric functions and their concomitant points of subjective equality (PSE). These functions were measured both when a neutral cue was presented in the middle of the display and transient attention was deployed via a peripheral cue to the location of one of the stimuli. Observers were told that the cues were uninformative as to the stimulus contrast or its orientation. We report two novel findings. First, apparent contrast is higher on the lower vertical meridian than on the upper. Second, the attentional enhancement of apparent contrast is asymmetrical with both low and high contrast stimuli; the effect of exogenous spatial attention is greater on the lower than the upper vertical meridian. As in prior studies, we find no corresponding asymmetry in orientation discrimination. Signal detection-based models explain the asymmetrical appearance effects as a function of differential multiplicative gain factors for the North and South locations, and predict a similar but much smaller asymmetry for orientation discrimination.
Stuart Fuller; Ruby Z Rodriguez; Marisa Carrasco
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Publication Detail:
Type:  Journal Article; Research Support, N.I.H., Extramural     Date:  2008-01-24
Journal Detail:
Title:  Journal of vision     Volume:  8     ISSN:  1534-7362     ISO Abbreviation:  J Vis     Publication Date:  2008  
Date Detail:
Created Date:  2008-03-05     Completed Date:  2008-03-20     Revised Date:  2014-09-15    
Medline Journal Info:
Nlm Unique ID:  101147197     Medline TA:  J Vis     Country:  United States    
Other Details:
Languages:  eng     Pagination:  16.1-16     Citation Subset:  IM    
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MeSH Terms
Attention / physiology*
Contrast Sensitivity / physiology*
Photic Stimulation
Space Perception / physiology*
Visual Perception / physiology*
Grant Support
R01 EY016200/EY/NEI NIH HHS; R01 EY016200-01A2/EY/NEI NIH HHS; R01-EY016200-01A2/EY/NEI NIH HHS

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