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| Volume 5, Number 11, Article 8, Pages 1024-1037 |
doi:10.1167/5.11.8 |
http://journalofvision.org/5/11/8/ |
ISSN 1534-7362 |
Unfocussed spatial attention underlies the crowding effect in indirect form vision
Hans Strasburger |
Generation Research Program, University of München Germany & Department of Medical Psychology, University of Göttingen Germany |
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Abstract
We studied mechanisms underlying the crowding effect in indirect form vision by measuring recognition contrast sensitivity of a character with flankers to the left and right. Attentional and featural contributions to the effect can be separated by a new paradigm that distinguishes pattern location errors from pattern recognition errors and further by manipulating the focusing of spatial attention through a positional cue, appearing 150 ms before the target. Measurements were on the horizontal meridian, at 1, 2, and 4 deg eccentricity, and a range of flankers' distances were used. Our results show that in normal indirect viewing, the impairment of character recognition by crowding is—in particular at intermediate flanker distances—caused to a large part by spatially imprecise focusing of attention. In contrast, the enhancement of performance by a transient positional cue seems mediated through a separate attentional mechanism such that attentional locus and focus are controlled independently. Our results furthermore lend psychophysical support to a separate coding of the what and where in pattern recognition.
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