Acoustic and phonetic discrimination in speech using event-related potentials: A mismatch negativity paradigm

The interaction of acoustic and phonetic discrimination in speech was studied using event-related potentials (ERPs). Participants consisted of 14 neurologically normal right-handed adults. Data were recorded in response to strong and weak acoustic changes signaling consonant distinctions, using a 64-channel encephalogram and a mismatch negativity (MMN) paradigm. The MMN is an automatic response evoked by stimulus change and is elicited when a train of repeated stimuli (standard) is interrupted by an oddball (deviant) stimulus. Stimuli consisted of one standard and two deviants that differed in their acoustic difference from the standard. All three stimuli were synthetic speech syllables in which F2 was manipulated to create a continuum between the syllables ‘‘ba’’ and ‘‘da.’’ The standard was the endpoint item ‘‘da.’’ The ‘‘strong deviant’’ was the ‘‘ba’’ endpoint item; the ‘‘weak deviant’’ was a more intermediate ‘‘ba’’ item, and therefore acoustically closer to the standard. MMNs were identified for both deviants, but the amplitude was smaller for the weak deviant condition. The data suggest that MMNs are sensitive to both phonetic change and also the magnitude of the acoustic difference within this change. The results are discussed with respect to theories of phonetic and acoustic discrimination in speech perception.