Attention modulates cortical, but not subcortical responses

Abstract

Organisms often need to attend to one signal within a crowded acoustic scene. While attentional effects in the auditory cortex are robust, what happens subcortically remains mysterious. We combined previous electroencephalography paradigms to measure whether attention modulates subcortical as well as cortical responses. Participants heard competing, temporally interleaved low and high melodies. Each melody had notes repeating at 2 Hz, with an overall note rate of 4 Hz. Participants attended to either the high- or low-pitched melody and responded whenever a 3-note pattern repeated in that stream. From past work, we expected to see strong cortical EEG responses at 2 Hz, but with a phase that shifted depending on which melody listeners attended. Importantly, we engineered the notes so that (1) low and high melodies excited different cochlear regions, and (2) each pitch period of each note elicited an auditory brainstem response (ABR). This allowed us to test whether attention altered responses along the ascending pathway in the brainstem. We found phase shifts in cortical responses with shifts of attention. While we found robust ABRs, we saw no evidence that attention modulated any of the ABR components. These results suggest that attentional effects in subcortical structures are weak, at best.