Electrophysiologic signs of attention versus distraction in a binaural listening task

Effects of active versus passive listening on the N1 and P2 components of the late auditory evoked potential were examined in 20 young adults following instructions to ignore and later to attend to different trains of frequent and deviant tones presented to one or both ears. To distinguish monaural from binaural neural refractory or recovery effects, monaural test runs were used to control for differences in stimulus-onset asynchronies (SOAs) between monaural and binaural runs. As expected, selective attention and monaural neuronal refractory effects were found. When attending the tones, listeners exhibited significantly larger P2, but not N1, amplitudes. During test runs with shorter monaural SOAs, listeners exhibited smaller N1 and P2 amplitudes than they did with longer SOAs. However, whether attending or nonattending, P2 amplitudes were smaller during binaural than monaural test runs, which suggests the possible existence of some form of "binaural" neuronal refractory or recovery effect. However, the absence of this binaural effect with the N1 component would suggest that binaural refractoriness, if it exists, involves different physiologic processes than monaural refractoriness.