Quantifying attentional modulation of auditory-evoked cortical responses from single-trial electroencephalography

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).

Concealed, Unobtrusive Ear-Centered EEG Acquisition: cEEGrids for Transparent EEG

“…The 3 s long sound streams originated from center, left and right locations and differed in a number of sound features as well as in the number of tones presented (3, 4, and 5, respectively). In this study, a replication of earlier multi-channel cap-EEG results (Choi et al, 2013) was possible with both high-density cap-EEG as well as cEEGrid ear-EEG. For both setups clear attention modulated ERPs in response to the attended sound stream were detected (Figure 5), and comparable single-trial classification accuracies at around 70% were achieved.…”

Cortical and Sensory Causes of Individual Differences in Selective Attention Ability Among Listeners With Normal Hearing Thresholds

“…For instance, any single recording of EEG or MEG is noisy, making it is hard to see specific events or to quantify attentional effects. However, by looking at which sound stream better predicts the evoked response to a short, 2-to 3-s-long recorded EEG or MEG pattern, it is possible to determine which source a listener is attending to (Choi, Rajaram, Varghese, & Shinn-Cunningham, 2013;Ding & Simon, 2012a, 2012bLalor & Foxe, 2010;O'Sullivan et al, 2014;Power, Foxe, Forde, Reilly, & Lalor, 2012;Rimmele, Zion Golumbic, Schroger, & Poeppel, 2015). Intracranial recordings (electrocorticography) in human listeners, which allow direct measurement of very localized brain activity, demonstrate the full power of attention on cortical encoding of speech in human listeners (e.g., Zion Golumbic, Ding, et al, 2013).…”

“…For example, the ability to decode attentional state from neural responses differs across listeners and correlates with differences in the strength of attentional modulation of the cortical response (e.g., Choi et al, 2013;O'Sullivan et al, 2014).…”

A right‐ear bias of auditory selective attention is evident in alpha oscillations

“…Auditory selectivity during DDL is believed to include enhancement of the attended stream and suppression of the unattended stream (Choi, et al, 2013; Golumbic et al, 2013; Chait, et al, 2010). Cortical oscillations within the alpha band are a key marker of selective attention thought to reflect suppression of task-irrelevant information in several sensory modalities (Payne & Sekuler, 2014).…”