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Carrasco, M., Ponte, D., Rechea,
C. & Sampedro, M.J. (1998). "Transient structures": The
effects of practice and distractor grouping ion within-dimension conjunction
searches. Perception & Psychophysics, 60(7): 1243-1258.
Abstract
It has been stated that whereas between-dimension (color x orientation)
conjunctions can be searched in a "parallel" fashion, within-dimension
(color x color) conjunctions are necessarily searched in a "serial
self- terminating" fashion (Wolfe et al., 1990). We explored the
effects of practice (within 1-h experimental session) and distractor grouping
on within-dimension conjunction search tasks. In Experiments 1 and 3,
the stimuli were rectangles formed by two adjacent squares; in Experiment
2, the stimuli were plus signs formed by two segments and an intersection.
In Experiments 1 and 2, observers were assigned to one of two experimental
conditions: In one, all the distractors shared a simple feature (the color
blue); in the other, distractors did not share that simple feature. In
the first condition, search became more efficient with practice and observers'
performance was characterized by a shallow reaction time (RT) x set size
slope; in the second condition, observers' performance did not improve
as much with practice. We propose that the differential effects of practice
between these two experimental conditions can be explained in terms of
distractor grouping induced by the shared color of the distractors. Experiment
3 showed that, with practice, a shallow RT x set size slope characterized
observers' search for a color x color target among four different distractors
that shared a common color. The present results contradict a main tenet
of some current visual search models--namely, that within- dimension conjunctions
cannot be searched in parallel, and question the validity of using RT
x set size slope functions to distinguish between preattentive versus
attentive search.
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