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Abstract:
Abstract: When single digit numerals are presented in
bimanual choice tasks, there exists a right-hand response advantage
with larger numbers and a left-hand advantage with lower numbers.
Dehaene et al. (1993) interpreted this phenomenon as a
spatial-numerical association of response codes (SNARC). Their
study suggested that number magnitude is represented as going in a
left to right direction and that the SNARC effect is due to a
spatial compatibility (Simon) effect between this internal analog
representation and the response effectors. However, since these
responses were made along a horizontal plane, we were curious to
examine in what direction the SNARC would manifest if responses
were oriented vertically, as Proctor (1990) observed an up-right,
down-left advantage using verbal stimuli. We were also interested
in whether analog magnitude representation could be different in
the two hemispheres. To test this, we used lateralized stimuli with
unimanual responses. When subjects were asked to judge the parity
of single digit numerals using vertically oriented response keys
with index/middle fingers indicating odd/even responses, they
showed a response advantage with the top key when given lower
stimulus numbers and an advantage with the bottom key with larger
numbers. This suggested that given vertically oriented responses,
number magnitude is represented going from top-down. There were no
significant differences between ipsilateral visual field/response
hands, suggesting a similar analog spatial representation of the
number line in the two hemispheres.
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