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Cerebral Cortex Advance Access originally published online on November 30, 2006
Cerebral Cortex 2007 17(9):2084-2093; doi:10.1093/cercor/bhl124
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© 2006 The Authors
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/2.0/uk/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Brain Mechanisms Implicated in the Preattentive Categorization of Speech Sounds Revealed Using fMRI and a Short-Interval Habituation Trial Paradigm

Marc F. Joanisse1, Jason D. Zevin2 and Bruce D. McCandliss2

1 Department of Psychology and Program in Neuroscience, The University of Western Ontario, London, Ontario N6A 5C2, Canada, 2 Sackler Institute for Developmental Psychobiology, Weill-Cornell Medical College, NY, USA

Address correspondence to email: marcj{at}uwo.ca.

A hallmark of categorical perception is better discrimination of stimulus tokens from 2 different categories compared with token pairs that are equally dissimilar but drawn from the same category. This effect is well studied in speech perception and represents an important characteristic of how the phonetic form of speech is processed. We investigated the brain mechanisms of categorical perception of stop consonants using functional magnetic resonance imaging and a passive short-interval habituation trial design (Zevin and McCandliss 2005). The paradigm takes advantage of neural adaptation effects to identify specific regions sensitive to an oddball stimulus presented in the context of a repeated item. These effects were compared for changes in stimulus characteristics that result in either a between-category (phonetic and acoustic) or a within-category (acoustic only) stimulus shift. Significantly greater activation for between-category than within-category stimuli was observed in left superior sulcus and middle temporal gyrus as well as in inferior parietal cortex. In contrast, only a subcortical region specifically responded to within-category changes. The data suggest that these habituation effects are due to the unattended detection of a phonetic stimulus feature.

Key Words: categorical perception • fMRI adaptation • middle temporal gyrus • speech perception • superior temporal gyrus

Funding to pay the Open Access publication charges for this article was provided by NSF grant REC-0337715 to BDM.


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