Cortical Responses Time-Locked to Continuous Speech in the High-Gamma Band Depend on Selective Attention.

Auditory cortical responses to speech obtained by magnetoencephalography (MEG) show robust speech tracking in the high-gamma band (70-200 Hz), but little is currently known about whether such responses depend on the focus of selective attention. In this study 22 human subjects listened to concurrent, fixed-rate, speech from male and female speakers, and were asked to selectively attend to one speaker at a time, while their neural responses were recorded with MEG. The male speaker's pitch range coincided with the lower range of the high-gamma band, whereas the female speaker's higher pitch range had much less overlap, and only at the upper end of high-gamma band. Neural responses were analyzed using the temporal response function (TRF) framework. As expected, the responses demonstrate robust speech tracking in the high gamma band, but only to the male's speech, with a peak latency of approximately 40 ms. The response magnitude also depends on selective attention: the response to the male speaker is significantly greater when male speech is attended than when it is not attended. This is a clear demonstration that even very early cortical auditory responses are influenced by top-down, cognitive, neural processing mechanisms.