[The influence of between-channel selection on the brain potentials related to within-channel selection in auditory...

Event-related potentials (ERPs) were recorded during a selective listening paradigm similar to a previous study (Okita, 1989). Stimuli were random sequences of five vowels and a tone pip in two "channels' (separated by location, left and right). The difficulty of between-channel selection was varied in discriminability of location, easy (EL) or hard (HL), whereas within-channel selection was manipulated by designating either tone (T), one vowel (1V), or two vowels (2V) as targets. Subjects were required to attend to one channel and detect targets therein. ERPs for the EL condition replicating the earlier study, confirmed the effects of within-channel selection on the early phase of attention-related negativity (Nd): the early Nd being larger, the higher the target/nontarget selection load. In the HL condition, however, the 1V/2V difference disappeared: the early Nd effect was reduced for 2V, but prolonged in duration for 1V. The interaction between selection processes of the between- and within-channel was discussed in relation to the allocation of limited attentional capacity for operations rechecking outcomes of a preattentive target-classification stage.