Comparison of behavioral discrimination, MMN, and P300 to speech and nonspeech stimuli

Abstract

Our objective is to examine the relation between central auditory processes and discrimination of speech (consonant–vowel) and nonspeech (frequency glide) stimuli. Behavioral responses and auditory evoked potentials (MMN and P300) of ten adults were evaluated to synthetically generated consonant–vowel (CV) speech and nonspeech contrasts. The CVs were two within-category stimuli and the nonspeech stimuli were two frequency glides whose frequencies matched the formant transitions of the CV stimuli. It was found that listeners exhibited significantly better behavioral discrimination to the nonspeech versus speech stimuli in same/different and oddball behavioral paradigms. MMN responses were present in all subjects to both stimulus contrasts, and were not significantly different with regard to stimulus type. P300’s were present in nine of ten subjects to both stimulus contrasts. However, the CV speech contrasts produced P300’s with significantly smaller amplitudes and longer latencies than those to the nonspeech stimuli. These results suggest that the stimuli were processed differently when measured behaviorally and with the P300, but not when measuring the MMN. The enhanced discrimination of the frequency glide stimuli versus the CV stimuli of analogous acoustical content supports the idea that different levels of processing mediate the auditory perception of speech versus nonspeech stimuli.