Brain mechanisms implicated in the preattentive categorization of speech sounds revealed using FMRI and a short-interval habituation trial paradigm.
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.
Joanisse
Marc F
MF
Department of Psychology and Program in Neuroscience, The University of Western Ontario, London, Ontario N6A 5C2, Canada. marcj@uwo.ca
Zevin
Jason D
JD
McCandliss
Bruce D
BD
D000161:Acoustic Stimulation; D000328:Adult; D001288:Attention / Q000502:physiology*; D001921:Brain / Q000503:physiopathology*; D003627:Data Interpretation, Statistical; D004192:Discrimination, Psychological / Q000502:physiology; D005260:Female; D006185:Habituation, Psychophysiologic / Q000502:physiology*; D006801:Humans; D007091:Image Processing, Computer-Assisted; D016014:Linear Models; D008279:Magnetic Resonance Imaging; D008297:Male; D013067:Speech Perception / Q000502:physiology*