The relationship between speech acoustics and cortical oscillations: An application of MEG coherence measures using auditory signals

Abstract

Event Abstract Back to Event The relationship between speech acoustics and cortical oscillations: An application of MEG coherence measures using auditory signals Jonathan E. Peelle1*, Joachim Gross2 and Matthew H. Davis1 1 INSERM, Ecole Normale Superieure, United Kingdom 2 University of Glasgow, Department of Psychology, United Kingdom Consistent phase relationships between information in the environment and neural signals has been demonstrated in a number of studies, primarily using motor, proprioceptive, and nociceptive stimuli. In the current study we investigated the relationship between oscillatory neural activity and acoustic stimuli (speech and nonspeech); specifically, we were interested in oscillatory coupling with the speech envelope (low frequency information in the speech signal) that plays an important role in speech identification. We used spoken sentences that were digitally processed using a noise-vocoding algorithm to manipulate intelligibility. Importantly, this approach preserves the temporal pattern of amplitude modulations across levels of intelligibility. Sentences were presented in random order to young adults with normal hearing acuity. After hearing each sentence, participants repeated as much as possible, providing a behavioral measure of trial-by-trial sentence intelligibility. We monitored neural activity using a 306-channel Elekta Neuromag MEG system. The data were analyzed using the DICS (dynamic imaging of coherent sources) algorithm [1], which quantifies the linear dependency of signals in the frequency domain. Computation of the neural-acoustic coupling revealed significant signal coherence between MEG signals and the amplitude envelope of speech in the 4-8 Hz range for intelligible speech. Source analysis suggests these signals originate along the superior and middle temporal gyri near to primary auditory cortex. Most importantly, we found that coherence was significantly impacted by speech intelligibility, suggesting that oscillatory coherence in auditory regions depends on linguistic content in addition to simple amplitude variation.