Target of selective auditory attention can be robustly followed with MEG

Selective auditory attention enables filtering relevant from irrelevant acoustic information. Specific auditory responses, measurable by electro- and magnetoencephalography (EEG/MEG), are known to be modulated by attention to the evoking stimuli. However, these attention effects are typically demonstrated in averaged responses and their robustness in single trials is not studied extensively. We applied decoding algorithms to MEG to investigate how well the target of auditory attention could be determined from single responses and which spatial and temporal aspects of the responses carry most of the information regarding the target of attention. To this end, we recorded brain responses of 15 healthy subjects with MEG when they selectively attended to one of the simultaneously presented auditory streams of words "Yes" and "No". A support vector machine was trained on the MEG data both at the sensor and source level to predict at every trial which stream was attended. Sensor-level decoding of the attended stream using the entire 2-s epoch resulted in a mean accuracy of 93% +/- 1% (range 83-99% across subjects). Time-resolved decoding revealed that the highest accuracies were obtained 200-350 ms after the stimulus onset. Spatially-resolved source-level decoding indicated that the cortical sources most informative of the attended stream were located in the primary auditory cortex, especially in the right hemisphere.