Attention differentially affects acoustic and phonetic feature encoding in a multispeaker environment.

Abstract

Humans have the remarkable ability to selectively focus on a single talker in the midst of other competing talkers. The neural mechanisms that underlie this phenomenon remain incompletely understood. In particular, there has been longstanding debate over whether attention operates at an early or late stage in the speech processing hierarchy. One way to better understand this is to examine how attention might differentially affect neurophysiological indices of hierarchical acoustic and linguistic speech representations. In this study, we do this by using encoding models to identify neural correlates of speech processing at various levels of representation. Specifically, using EEG recorded during a "cocktail party" attention experiment, we show that phonetic feature processing is evident for attended, but not unattended speech. Furthermore, we show that attention specifically enhances isolated indices of phonetic feature processing, but that such attention effects are not apparent for isolated measures of acoustic processing. These results provide new insights into the effects of attention on different pre-lexical representations of speech, insights that complement recent anatomical accounts of the hierarchical encoding of attended speech. Furthermore, our findings support the notion that - for attended speech - phonetic features are processed as a distinct stage, separate from the processing of the speech acoustics.