Exploring Neurophysiological Bases of Speech Discrimination and Categorization Processes

Abstract:
Abstract: Neurophysiological studies using the oddball paradigm have demonstrated that the Mismatch Negativity (MMN) and its neuromagnetic counterpart, the Mismatch Field (MMF), are good neural indicators for speech discrimination and sound discrimination in general. This study combines the Even Related Potential (ERP) technique and Magnetoencephalography (MEG) to further explore the neural bases of speech discrimination and categorization. Two sets of speech stimuli, a continuum of synthetic /ba-wa/ syllables, and a synthetic /ra-la/ continuum, were used. Identification and discrimination data and ERP data were collected from 10 American subjects. Behavioral and MEG data were collected from 10 Japanese subjects and 1 American subject. The American behavioral data showed typical categorical perception for both stimulus sets whereas the Japanese behavioral data showed categorical perception for /ba-wa/ but not for /ra-la/, confirming earlier findings about the role of linguistic experience in speech perception. Results of ERP and MEG data indicate that both MMN and MMF measures appear to reflect not just sound discrimination but a pre-attentive neural phonetic categorization process that is shaped by prior linguistic exposure.