MISMATCH NEGATIVITY IN THE NEUROPHYSIOLOGIC BEHAVIORAL-EVALUATION OF AUDITORY PROCESSING DEFICITS - A CASE-STUDY

The subject of this case report is an 18-year-old woman with grossly a bnormal auditory brain stem response (ABR), normal peripheral hearing, and specific behavioral auditory processing deficits. Auditory middle latency responses (MLRs) and cortical potentials N1, P2, and P300 wer e intact. The mismatch negativity (MMN) was normal in response to cert ain synthesized speech stimuli and impaired to others-consistent with her behavioral discrimination of these stimuli. Behavioral tests of au ditory processing were consistent with auditory brain stem dysfunction . A neuropsychological evaluation revealed normal intellectual and aca demic performance. The subject was in her first year of college at the time of the evaluation. This case study is important because: (1) Alt hough there have been several reports of absent/abnormal ABR with pres erved peripheral hearing and deficits in auditory processing, little i s known about the specific nature of the auditory deficits experienced by these individuals. Such information may be valuable to the clinica l management of patients with this constellation of findings. (2) Of i nterest is the information that the mismatch negativity (MMN) cortical event-related potential can bring to the evaluation of patients with auditory processing deficits. The MMN reflects central auditory proces sing of small acoustic differences and may provide an objective measur e of auditory discrimination. (3) From a theoretical standpoint, a pat ient with neural deficits affecting specific components of the auditor y pathway provides insight into the relationship between evoked potent ials and physiological mechanisms of auditory processing. How do vario us components of the auditory pathway contribute to speech discriminat ion? How might evoked potentials reflect the processes underlying the neural coding of specific features of speech stimuli such as timing an d spectral cues?