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Abstract:
Earlier encounters with an object facilitate later processing
of that stimulus. This "priming" may be decreased by changes in the
object's perceptual form. To explore the functional-anatomic
correlates of such perceptual specificity, we used event-related
fMRI methods that permit rapid intermixed trial presentation to
examine neural activity when participants made size judgments
regarding previously presented objects (Same), novel exemplars of
previously presented objects (Different), or entirely new objects
(New) (BOLD fMRI, 3.0T GE scanner with ANMR EPI, 16 axial slices,
TR=2 sec, N=14). Behavioral response latencies showed the expected
pattern of new > different > same. fMRI results comparing
same and new showed decreased activation, reflecting priming, in
multiple regions, including bilateral posterior inferior frontal,
superior occipital, fusiform, medial temporal, frontal opercular,
and anterior left inferior frontal cortices. A subset of these
regions also showed reductions in the different vs. new comparison,
including bilateral frontal opercular, anterior left inferior
frontal, and left medial temporal areas. Direct comparison of same
and different showed greater reductions in bilateral posterior
inferior frontal, superior occipital, fusiform, and medial temporal
regions for identical vs. changed exemplars. Thus, intermediate
levels of repetition priming found behaviorally for perceptually
altered stimuli were correlated with intermediate and somewhat
selective reductions in neural activity.
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