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Abstract:
Three-dimensional structural representations are critical for
object recognition, and the degree to which objects overlap in
structure within a category determines the efficacy of recognition.
Functional neuroimaging studies of object recognition are providing
converging evidence that lateral occipital and posterior fusiform
regions are involved in processing structural descriptions;
however, processing object structure was not directly manipulated
in some of these studies. The present study examines parametrically
varied structural similarity (SS) of object pairs to establish
behavioral and neuroimaging profiles modulated by structural object
processing. Eight participants viewed two animal pictures
simultaneously. On "yes" trials, the two pictures represented the
same animal and on "no" trials the two animals were different. On
"no" trials, the animal pairs parametrically varied across four
levels of SS, as determined by normative similarity ratings). Mean
pair-wise similarity rating were 183, 422, 539 and 736 (on a scale
of 1000) for SS1, SS2, SS3 and SS4 objects, respectively. Decision
latencies and errors increased as SS level increased, F(3,3) =
10.8, p < .05, F(3,3) = 61.7, p < .01, respectively, such
that discriminating "dolphin" from "spider" (low in SS) was much
faster and more accurate than discriminating "rhino" from "hippo"
(high in SS). Initial fMRI data in individual subjects shows strong
modulation of lateral occipital and posterior fusiform regions by
SS level, in agreement with previous functional imaging
studies.
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