The ability of left-hemisphere stroke patients (n
= 8) and healthy control subjects (n = 8) to process
sounds preattentively and attentively was studied by recording
auditory event-related potentials (ERPs) and behavioral
responses. For the right-ear stimulation, the mismatch
negativity (MMN) was significantly smaller in the patients
than control subjects over both hemispheres. For the left-ear
stimuli, the MMN was significantly smaller in the patient
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 the reduction being
larger over the left hemisphere), whereas no significant
effects on the N1 amplitude were found for the left-ear
stimulation. Behaviorally, the patients detected significantly
fewer deviant tones than did the 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 accuracy can be separately determined
for the left and right temporal lobes.