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Abstract:
Inhibition of return (IOR) is the demonstration that subjects
are slower to respond to a stimulus when it appears at a previously
stimulated location relative to when it appears at a new location.
In a previous exogenous cueing experiment, we found that IOR was
associated with a reduction of the occipital P1 component of the
visual evoked potential (McDonald et al., 1996, CNS). However, one
consideration that affects all such studies is that sensory
interactions between the cue and target are likely to be different
on valid and invalid trials, and thus the observed effects might
simply reflect sensory refractoriness. In the present experiment,
we reduced the strength of sensory interactions in order to help
interpret the evoked potential effects associated with IOR.
Specifically, the subjects viewed the display through a dichoptic
viewing apparatus so that the cue and target stimuli appeared in
different eyes. The stimuli also appeared at different locations
and in different colors and shapes to reduce sensory interactions
at binocular stages of the visual system. At long (500-700 ms)
cue-target intervals, IOR was accompanied by a reduction of the
occipital P1 on valid trials compared to invalid trials. This
provides the first evoked-potential sign of IOR that is not likely
to be caused by sensory refractoriness. We conclude that IOR
between visual stimuli partly reflects suppression of perceptual
processing.
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