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Abstract

Previous studies have proposed that learning contributes to the recognition of biological
movements. We investigated the neural correlates of these learning processes in an
event-related fMRI adaptation experiment. This paradigm entails repeated presentation
of a stimulus resulting in decreased fMRI responses, compared to stronger responses
after a change in a stimulus dimension indicating selectivity of an area to this changed
dimension.
Novel biological movements were generated by linear combination of triples of
prototypical trajectories of human movements (Giese Poggio, 2000). Subjects had to
discriminate between identical, very similar, moderately similar and completely different
point-light stimulus pairs. By choosing appropriate weight vectors the difficulty of the
discrimination task could be accurately controlled. The subjects were scanned before
and after a training period of three days. Areas relevant to the processing of biological
motion (early visual areas, hMT+/V5, KO, FFA, and STSp) were localized as regions of
interest using standard mapping techniques.
Before training, the observers discriminated successfully between the stimuli in the
moderately similar and completely different stimulus pairs but not between the very
similar pairs. Consistent with these psychophysical data, we observed significantly
stronger fMRI responses for moderately similar and completely different stimulus pairs
but not for very similar pairs compared to identical pairs in the FFA and STSp. However,
after training the observers’ discrimination performance for very similar stimulus pairs
improved and significantly stronger fMRI responses were observed for this condition
compared to identical stimulus pairs in all the higher visual areas. These results suggest
that learning tunes neural populations in the STS and FFA for the discrimination of
novel biological movements.