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Eye movements selective for spatial frequency and orientation during active visual search
A. Tavassoli, I. van der Linde, A.C. Bovik and L.K. Cormack
Vision Research
Abstract
Visual search can simply be defined as the task of looking for objects of interest in cluttered visual environments.
Typically, the human visual system succeeds at this by making a series of rapid eye movements
called saccades, interleaved by discrete fixations. However, very little is known on how the
brain programs saccades and selects fixation loci in such naturalistic tasks. In the current study, we
use a technique developed in our laboratory based on reverse-correlation1 and stimuli that emulate
the natural visual environment to examine observers’ strategies when seeking low-contrast targets of
various spatial frequency and orientation characteristics. We present four major findings. First, we provide
strong evidence of visual guidance in saccadic targeting characterized by saccadic selectivity for spatial
frequencies and orientations close to that of the search target. Second, we show that observers exhibit
inaccuracies and biases in their estimates of target features. Third, a complementarity effect is generally
observed: the absence of certain frequency components in distracters affects whether they are fixated or
mistakenly selected as the target. Finally, an unusual phenomenon is observed whereby distracters containing
close-to-vertical structures are fixated in searches for nonvertically oriented targets. Our results
provide evidence for the involvement of band-pass mechanisms along feature dimensions (spatial frequency
and orientation) during visual search.
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