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Abstract:
Abstract: Previous studies have reported better performance
on visual tasks in the inferior visual field (IVF) as compared to
the superior visual field (SVF). This asymmetry has been attributed
to various factors, including differences in processing (Previc,
1990) and allocation of attention (Carrasco et al., 1998) between
the vertical hemifields. To investigate directly whether vertical
visual field asymmetries for motion processing are perceptual or
attentional in nature, we obtained thresholds on a
direction-of-motion task using a stochastic motion display
presented in one of the four quadrants of visual space, randomly
across trials. Two display types were employed: "single" in which
the motion target was presented alone, and "multiple" in which the
motion target was presented in one quadrant while the other three
quadrants contained randomly moving dots ("distractors"). No
asymmetry was found in the single condition, suggesting that motion
processing capabilities are equivalent in the SVF and IVF. In the
multiple condition, however, a significant IVF over SVF advantage
was observed, suggesting that attention is drawn to the IVF when
the visual field contains multiple potential targets. In addition,
in the multiple condition subjects often could discern direction of
motion even when the location of the target was not obvious. This
ability to access directional, at the expense of location,
information may arise if subjects monitor directionally-selective
neural mechanisms with large receptive fields.
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