Discontinuity of early and late event-related brain potentials for selective attention in dichotic listening.

If a representation of an auditory attention channel was present in the auditory cortices but not in the subcortical structures, it would be predicted that the early event-related brain potential (ERP) would disagree with the late ERP in selective attention effects. To examine this idea, the present study recorded the auditory brain stem response (ABR) as an early ERP and also the negative difference, the processing negativity and the irrelevant positive difference waves as late ERPs during dichotic listening. Each participant experienced two dichotic conditions: (i) 500-Hz standard tones to the left ear and 1000-Hz ones to the right ear (L500/R1000), (ii) 1000-Hz standard tones to the left ear and 500-Hz ones to the right ear (L1000/R500). In a control task, participants performed visual detection and ignored auditory stimuli. Although the negative difference and processing negativity were found to be identical between the two dichotic conditions, the ABR demonstrated a significant difference between relevant and irrelevant tasks only for the L500/R1000 condition. A response preference to lower-frequency tones was found for behavioural measures and late ERPs but not for the ABR. These results suggest difficulty in representing attention channels in the auditory brain stem. In addition, a weak effect of dichotic sound combination in behaviours corresponded only with earlier ERPs.