A comparison of the mismatch negativity (MMN) event-related potential to tone and speech stimuli in normal and aphasic adults

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Abstract
We evaluated the mismatch negativity (MMN) event-related potential (ERP) in normal and aphasic adults to tone and speech stimuli to determine aphasic patients' auditory discrimination and the relationship between MMN measures and severity of aphasia. MMNs were present in 89% of normal subjects and 79% of aphasic subjects to tone stimuli. MMNs were present in 100% of normal subjects and 54% of aphasic subjects to speech stimuli. The duration of the MMN ERP to speech stimuli was significantly related to severity of aphasia on the Western Aphasia Battery, Porch Index of Communicative Ability, and the Token Test. Thus, not all aphasic people show an early, preconscious orientation response to tone and speech stimuli. However, the duration of this response, when present, to speech stimuli appears to be related to the severity of aphasia.