Unfocused spatial attention underlies the crowding effect in indirect form vision

J Vis. 2005 Dec 29;5(11):1024-37. doi: 10.1167/5.11.8.

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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Attention*
  • Contrast Sensitivity
  • Cues
  • Humans
  • Photic Stimulation / methods*
  • Psychophysics
  • Sensory Thresholds
  • Space Perception*
  • Vision, Ocular*