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Suppression of Competing Speech through Entrainment of Cortical Oscillations

Suppression of Competing Speech through Entrainment of Cortical Oscillations

Authors: 
Cort Horton, Mike D'Zmura & Ramesh Srinivasan
Year: 
2013
Journal: 
Journal of Neurophysiology
Abstract: 

People are highly skilled at attending to one speaker in the presence of competitors, but the neural mechanisms supporting this remain unclear. Recent studies have argued that the auditory system enhances the gain of a speech stream relative to competitors by entraining (or "phase-locking") to the rhythmic structure in its acoustic envelope, thus ensuring that syllables arrive during periods of high neuronal-excitability. We hypothesized that such a mechanism could also suppress a competing speech stream by ensuring that syllables arrive during periods of low neuronal-excitability. To test this, we analyzed high-density EEG recorded from human adults while they attended to one of two competing, naturalistic speech streams. By calculating the cross-correlation between the EEG channels and the speech envelopes, we found evidence of entrainment to the attended speech's acoustic envelope, as well as weaker yet significant entrainment to the unattended speech's envelope. An ICA decomposition of the data revealed sources in the posterior temporal cortices that displayed robust correlations to both the attended and unattended envelopes. Critically, in these components the signs of the correlations when attended were opposite those when unattended, consistent with the hypothesized entrainment-based suppressive mechanism.

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