Behavioral/Systems/Cognitive Categorical Speech Processing in Broca’s Area: An fMRI Study Using Multivariate Pattern-Based Analysis

Althoughmuch effort has beendirected towardunderstanding the neural basis of speech processing, the neural processes involved in the categorical perception of speech have been relatively less studied, and many questions remain open. In this functional magnetic reso-nance imaging (fMRI) study, we probed the cortical regionsmediating categorical speech perception using an advanced brain-mapping technique, whole-brain multivariate pattern-based analysis (MVPA). Normal healthy human subjects (native English speakers) were scanned while they listened to 10 consonant–vowel syllables along the /ba/–/da / continuum. Outside of the scanner, individuals ’ own category boundaries were measured to divide the fMRI data into /ba / and /da / conditions per subject. The whole-brain MVPA revealed that Broca’s area and the left pre-supplementarymotor area evoked distinct neural activity patterns between the two perceptual catego-ries (/ba / vs /da/). Broca’s areawas also foundwhen the sameanalysiswas applied to another dataset (Raizada andPoldrack, 2007),which previously yielded the supramarginal gyrus using a univariate adaptation–fMRI paradigm. The consistent MVPA findings from two independent datasets strongly indicate that Broca’s area participates in categorical speech perception, with a possible role of translating speech signals into articulatory codes. The difference in results between univariate andmultivariate pattern-based analyses of the same data suggest that processes indifferent cortical areas along thedorsal speechperception streamaredistributedondifferent spatial scales