Journal of Neuroscience, Vol 14, 554-567, Copyright © 1994 by Society for Neuroscience
Visual search among items of different salience: removal of visual attention mimics a lesion in extrastriate area V4
J Braun
California Institute of Technology, Division of Biology, Pasadena 91125.
In more than one respect, visual search for the most salient or the least
salient item in a display are different kinds of visual tasks. The present
work investigated whether this difference is primarily one of perceptual
difficulty, or whether it is more fundamental and relates to visual
attention. Display items of different salience were produced by varying
either size, contrast, color saturation, or pattern. Perceptual masking was
employed and, on average, mask onset was delayed longer in search for the
least salient item than in search for the most salient item. As a result,
the two types of visual search presented comparable perceptual difficulty,
as judged by psychophysical measures of performance, effective stimulus
contrast, and stability of decision criterion. To investigate the role of
attention in the two types of search, observers attempted to carry out a
letter discrimination and a search task concurrently. To discriminate the
letters, observers had to direct visual attention at the center of the
display and, thus, leave unattended the periphery, which contained target
and distractors of the search task. In this situation, visual search for
the least salient item was severely impaired while visual search for the
most salient item was only moderately affected, demonstrating a fundamental
difference with respect to visual attention. A qualitatively identical
pattern of results was encountered by Schiller and Lee (1991), who used
similar visual search tasks to assess the effect of a lesion in
extrastriate area V4 of the macaque.
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