Cross-Frequency Coupling in Cortical Processing of Speech.

This study examines power-power cross-frequency coupling (CFC) between different frequency bands of cortical activity in normal-hearing (NH) listeners and its association to the processing temporal envelope (ENV) and temporal fine structure (TFS) of speech. CFC between alpha and theta bands and between gamma and theta bands was investigated when only ENV or TFS or the original speech itself were processed. Comparing the cortical activity in response to ENV and original speech, there was an increase in alpha-theta CFC and in gamma-theta CFC when listening to ENV alone. However, when comparing the response when to listening TFS alone, there was a reduction in gamma-theta CFC compared to the original speech and the alpha-theta CFC was comparable to the equivalent observed with original speech. The increase in CFC may suggest that there is more synchrony across different bands of cortical activity in processing ENV than TFS. These measures can serve as indicators when either ENV or TFS is perceived.