Dept. of Commun. Sci. & Disord., Searle Bldg., 2299 N. Campus Dr., Northwestern Univ., Evanston, IL 60208
Behavioral and neurophysiologic correlates of pitch and phoneme perception were investigated in a 42-year-old male with a unilateral cortical lesion (due to left hemisphere frontal-temporal-parietal craniotomy). Functional impairment of his speech perception ability was reflected in his behavioral performance. Electrophysiologic measures (ABR, MLR, MMN) were used to assess the underlying neurophysiologic processes. In the behavioral experiment the stimuli were synthesized syllables differing in place of articulation (/da/, /ga/) and pitch (high, low). The pitch and place differences were equally discriminable. A same-different behavioral discrimination task revealed that the subjects discrimination of pitch was intact, however his discrimination of place was severly impaired. The mismatch negativity (MMN) auditory-evoked potential is a pre-attentive neurophysiologic index of acoustic change. Of interest was whether the MMN would reflect the selective impairment in phonetic perception at a pre-attentive level. Results revealed that the MMN was elicited by pitch differences in speech stimuli but not by place differences (i.e., consistent with behavioral discrimination). Thus the MMN appears to reflect the distinct neuroanatomic sites that underlie processing of different auditory stimulus attributes. Theoretical implications for neurophysiologic processes underlying pitch and place of articulation perception will be discussed.