Unfocused spatial attention underlies the crowding effect in indirect form vision.
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.
Strasburger
Hans
H
Generation Research Program, University of München, Germany. Strasburger@uni-muenchen.de
D001288:Attention; D015350:Contrast Sensitivity; D003463:Cues; D006801:Humans; D010775:Photic Stimulation / Q000379:methods*; D011601:Psychophysics; D012684:Sensory Thresholds; D013028:Space Perception; D014785:Vision, Ocular