Abstract
Selective auditory attention is essential for human listeners to be able to communicate in multi-source environments. Selective attention is known to modulate the neural representation of the auditory scene, boosting the representation of a target sound relative to the background, but the strength of this modulation, and the mechanisms contributing to it, are not well understood. Here, listeners performed a behavioral experiment demanding sustained, focused spatial auditory attention while we measured cortical responses using electroencephalography (EEG). We presented three concurrent melodic streams; listeners were asked to attend and analyze the melodic contour of one of the streams, randomly selected from trial to trial. In a control task, listeners heard the same sound mixtures, but performed the contour judgment task on a series of visual arrows, ignoring all auditory streams. We found that the cortical responses could be fit as weighted sum of event-related potentials evoked by the stimulus onsets in the competing streams. The weighting to a given stream was roughly 10 dB higher when it was attended compared to when another auditory stream was attended; during the visual task, the auditory gains were intermediate. We then used a template-matching classification scheme to classify single-trial EEG results. We found that in all subjects, we could determine which stream the subject was attending significantly better than by chance. By directly quantifying the effect of selective attention on auditory cortical responses, these results reveal that focused auditory attention both suppresses the response to an unattended stream and enhances the response to an attended stream. The single-trial classification results add to the growing body of literature suggesting that auditory attentional modulation is sufficiently robust that it could be used as a control mechanism in brain–computer interfaces (BCIs).
Highlights
Most human listeners are able to selectively attend to a target sound in a complex scene with relative ease
A salient effect of selective auditory attention is the enhancement of the N1 event related potentials (ERPs) component evoked by an attended sound (e.g., Hillyard et al, 1973), which, given its 100 ms latency suggests it is generated in early auditory sensory cortex (Scherg et al, 1989)
QUANTIFYING AUDITORY ATTENTION When listeners need to analyze the spectrotemporal content of a sound source in the presence of simultaneous, competing sources, they must sustain selective attention on the target source
Summary
Most human listeners are able to selectively attend to a target sound in a complex scene with relative ease. Though the specific mechanisms supporting these processes are not well understood, gross changes in neural activity due to attention can be observed in auditory-evoked event related potentials (ERPs) measured using electroencephalography (EEG; e.g., Hillyard et al, 1973; Hansen and Hillyard, 1980; Woldorff et al, 1987). Such studies find changes in the amplitude and shape of ERPs, suggesting that selective attention acts as a gain on neural activity, causing a relative enhancement of the representation of attended sensory inputs and a relative decrease in the representation of unattended or ignored inputs (Hillyard et al, 1998). The idea that selective auditory attention strongly modulates the neural representation of sound in sensory auditory cortex is supported by MEG studies (Woldorff et al, 1993; Alho et al, 2012; Ding and Simon, 2012) and fMRI data (Grady et al, 1997; Jäncke et al, 1999; Janata et al, 2002)
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