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Abstract:
The present experiment tested the hypothesis that a right
hemisphere advantage for coordinate spatial processing depends on
coarse coding mechanisms in low-level vision. Thirty right-handed
participants performed the categorical judgment (whether the target
is above/below a bar) and the coordinate judgment (whether the
target is within 2 cm from a bar) on stimuli presented to either
the left visual field/right hemisphere (LVF/RH) or the right visual
field/left hemisphere (RVF/LH). We manipulated stimulus display
(bright vs. contrast-balanced), and distance between stimulus
components (near, middle, and far). It is hypothesized that precise
metric information, which is effectively processed by coarse coding
mechanisms, would be required when the coordinate judgment was made
on the middle distances (1.5 - 2.5cm). Error data indicated that a
Task by Visual Field interaction and a LVF/RH advantage for the
coordinate task were observed only for the middle distance
condition: A RVF/! ! LH advantage for the categorical task was
observed for both bright and contrast-balanced stimuli, whereas a
LVF/RH advantage for the coordinate task was observed for the
bright stimuli but not for the contrast-balanced stimuli. It is
known that low spatial frequencies, useful for coarse coding, are
eliminated by contrast-balancing. Thus, these results suggest that
there is a direct link between coarse coding mechanisms and the
right hemisphere advantage for the coordinate spatial
processing.
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