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Abstract:
Abstract: Recently, we reported a left hemisphere advantage
in deaf, but not hearing, subjects on a motion discrimination task
(Bosworth & Dobkins, 1999). To investigate whether this visual
field asymmetry is due to altered motion processing or visual
attention, we obtained direction-of-motion thresholds from deaf and
hearing subjects under various conditions of attentional demand. If
the asymmetry found in deaf subjects can be explained by
attentional factors, it should depend upon the focus of spatial
attention (i.e., narrow or broad). A stochastic motion display was
presented in one of the four quadrants of visual space, randomly
across trials. Subjects reported direction of moving dots in a
2-AFC task. Stimulus location was either unpredictable or preceded
by a pre-cue, which directed attention toward stimulus location.
Two display conditions were used to manipulate attentional focus:
1) single: only the motion target was presented in one quadrant; 2)
multiple: the motion target was presented simultaneously with three
noise displays in the remaining quadrants. Consistent with our
earlier work, deaf subjects exhibited lower thresholds and faster
reaction times for the right compared to the left visual field,
whereas hearing subjects exhibited no asymmetry. The strength of
this hemispheric asymmetry in deaf subjects was not modulated by
attentional manipulations, suggesting this asymmetry is perceptual.
We are currently investigating whether this asymmetry is due to
sign language experience or auditory deprivation.
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