The processing of sound duration after left hemisphere stroke: Event-related potential and behavioral evidence

The ability of left-hemisphere stroke patients (n = 8) and healthy control subjects (n = 8) to process sounds preattentively and attentively was studi ed by recording auditory event-related potentials (ERPs) and behavioral res ponses. For the right-ear stimulation. the mismatch negativity (MMN) was si gnificantly smaller in the patients than control subjects over both hemisph eres. For the left-ear stimuli, the MMN was significantly smaller in the pa tient group than in the control group over the left hemisphere, whereas no group differences were obtained over the right hemisphere. In addition, the N1 amplitude was reduced bilaterally For the right-ear stimulation (with t he reduction being larger over the left hemisphere). whereas no significant effects on the N1 amplitude were found for the left-ear stimulation. Behav iorally, the patients detected significantly fewer deviant tones than did t he control subjects irrespective of the stimulated ear. The present results thus suggest that the long-latency ERPs can be used to probe such auditory processing deficits that are difficult to define with behavioral measures. Especially by recording MMN to monaural stimuli, the discrimination accura cy can be separately determined for the left and right temporal lobes.