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Abstract:
Imaging and monkey research has shown that object observation
activates, regardless of any intention to grasp, the ventrolateral
premotor area (vPMC) involved in hand functions. We present two
whole-brain fMRI studies to test the hypothesis that pragmatic
physical properties of attended objects are reflected by vPMC
activation. In both studies, 12 healthy subjects were required to
detect and indicate deviant objects in a visual sequential
paradigm. No object-related actions were required, but only
perceptual monitoring. Baseline tasks not related to the object
information controled for perceptual input, general attention
effort and response output. In Experiment 1, object size was
manipulated (small/graspable (S condition) vs. big/nongraspable (B
condition)). In Experiment 2, object contour was manipulated
(contour/graspable (C condition) vs. non-contour/nongraspable (N
condition)). In both experiments, all object tasks elicited vPMC
activation relative to the baseline task. However, neither the
direct task contrast between S and B, nor that between C and N
revealed any premotor activations. In contrast, stimulus
manipulations modulated activations only within posterior visual
areas. Our findings confirm the assumption that attentive object
observation is reflected by premotor "hand field" activation.
However, since object graspability appeared to have no influence on
this activation, premotor representations seem to be more abstract,
i.e., less dependent on pragmatic properties as supposed.
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