Categorical perception (CP) is a mechanism whereby non-identical stimuli that have the same underlying meaning become invariantly represented in the brain. Through behavioral identification and discrimination tasks, CP has been demonstrated to occur broadly across the auditory modality, including in perception of speech (e.g. phonemes) and music (e.g. chords) stimuli. Several functional imaging studies have linked CP of speech with activity in multiple regions of the left superior temporal sulcus (STS). As language processing is generally left-hemisphere dominant and, conversely, fine-grained spectral processing shows a right hemispheric bias, we hypothesized that CP of musical stimuli would be associated with right STS activity. Here, we used functional magnetic resonance imaging (fMRI) to test healthy, musically-trained volunteers as they (a) underwent a musical chord adaptation/habituation paradigm and (b) performed an active discrimination task on within- and between-category chord pairs, as well as an acoustically-matched, more continuously-perceived orthogonal sound set. As predicted, greater right STS activity was linked to categorical processing in both experimental paradigms. The results suggest that the left and right STS are functionally specialized and that the right STS may take on a key role in CP of spectrally complex sounds.
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