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Abstract:
Attention to discrete visual objects was assessed in human
areas V1 and V2 with functional Magnetic Resonance Imaging (fMRI).
Subjects attended to single oriented line segments of various
sizes, patches of color, and rotated Ts constructed from
conjunctions of small line segments. The rotated Ts were attended
both in single displays and in displays with distractor stimuli.
Three common views of attentional selection were examined: an
attentional stage model, a resource competition model and a
perceptual gain model. Attentional effects were seen in area V1
when the attended stimuli were small line segments or conjunctions
of small line segments but not when stimuli were larger line
segments or color patches. Attention effects were much larger for
conjunction stimuli than single-feature stimuli. Attention was seen
in area V2 for all stimulus conditions. Attention effects were
larger when distractor items were present. The results support a
multiple mechanism view of attentional selection in which area V2
is the default starting location for cortical attentional
modulation. Additionally, attention tunes perceptual processing in
areas which are specialized for processing features that define an
attended stimulus. Stimulus competition also affects the strength
of attentional modulation but at a scale which exceeds the level of
the classical receptive field.
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