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Abstract:
Abstract: Double dissociations between processing living
things and man-made objects have been found in the behavior of
brain-damaged patients and in brain-activation patterns in
neuroimaging studies. However, it is still unclear what accounts
for these dissociations. We tested the hypothesis that a key
explanatory variable is whether people normally "manipulate" an
item - i.e., whether they physically interact with it. In general,
man-made objects are manipulated more than living things. The
observed dissociations may therefore reflect this correlation. We
constructed frequency-matched word lists of manipulated and
non-manipulated living (e.g., rabbit, monkey) and man-made (e.g.,
sword, castle) things. Right-handed adults named aloud pictures of
these items in a Siemens 1.5T scanner. Functional volumes were
collected after each four-item block of a given condition was
displayed. Initial analyses, using SPM, focussed on regions
yielding activation increases for manipulated versus
non-manipulated items, across both living and man-made things.
Given previous reports of activation increases for man-made versus
living things in left premotor cortex and in the region of the
posterior middle temporal gyrus, these two areas were identified as
regions of interest. Preliminary analyses of individual subjects
showed that for both living and man-made things, both regions
showed increased activation for manipulated versus non-manipulated
items. These data support the hypothesis that an important variable
in explaining living/man-made dissociations is whether the item is
commonly manipulated.
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