Unraveling the effects of selective auditory attention in ERPs: From the brainstem to the cortex.

A little over fifty years ago, it was reported that selectively attending to one of two dichotically presented tone sequences enhances the major N1 component of the cortical event-related potential (ERP) to the attended tones. The present study revisited this classic experiment but replaced the tones in one ear with frequency-modulated "chirps" that were designed to activate the entire cochlea simultaneously and thereby elicit robust ERPs in the auditory brainstem pathways. Participants attended selectively to the sounds in one ear at a time with the task of reporting occasional targets of lower intensity. When chirps were attended, they elicited enhanced ERPs at multiple levels of the auditory pathways (0-250ms), including a brainstem response at the level of the inferior colliculus. These results help to resolve a long-standing question of whether selective attention exerts top-down control over the initial transmission of competing auditory inputs in the brainstem pathways.