Testing the Limits of the Stimulus Reconstruction Approach: Auditory Attention Decoding in a Four-Speaker Free Field Environment

Auditory attention can be defined as the cognitive process that enables us to selectively focus on relevant aspects of the acoustic environment while other aspects are ignored. The remarkable ability of the auditory system to focus on one out of several speakers in a multispeaker environment has become known as the cocktail party effect. Although the neural processes underlying selective auditory attention (SAA) are not well understood, it has recently been shown that the cortical representation of a listener’s attended sound stream can be recorded noninvasively from the scalp and that stimulus reconstruction from single trial electroencephalographic (EEG) data enables the decoding of the orientation of auditory attention. The present study extends this approach by evaluating its efficacy in a naturalistic and challenging four-speaker acoustic free field environment, in which the four speakers were spatially separated and presented different but equally salient spoken messages to the listeners. Ten participants were instructed to focus SAA on a spoken prose message in one of the four loudspeakers while ignoring the remaining three streams of prose. Concurrent EEG activity recorded via 128 scalp channels was used for a stimulus reconstruction analysis. The results showed that this approach can be used to decode the orientation of SAA even in a complex and realistic acoustic setting. To confirm that the successful decoding was driven by correspondences between the recorded EEG activity and the attended speech envelopes, the analysis method was validated against randomly constructed sets of surrogate data and by correlations with behavioral data.