MEG Responses to Speech and Stimuli With Speechlike Modulations

Acoustic signals can be decomposed into the product of an envelope and its fine structure. The envelope features are critical to speech recognition. Results from human behavioral and psychophysical experiments indicate that magnetoencephalography (MEG) responses can significantly phase-lock to the temporal envelope of an auditory stimulus, and speech comprehension is correlated with this phase locking. The goal of this study is to explore the properties of neural response to the speech and stimuli with complex temporal envelopes. Five auditory stimuli with the same envelope, generated from natural speech, and the same stimuli but with the envelope artificially sped up were presented to two subjects. Auditory evoked responses were recorded with a whole-head 160-channel MEG system. Independent component analysis (ICA), principle component analysis (PCA) and equivalent current dipole fitting were performed to separate and identify the neural sources (and artifacts). The result shows that the location, orientation, and strength of the neural sources are robust across all stimuli, with correlation between auditory responses and the temporal envelope of the stimuli. These results provide support for the premise that neurons in the auditory cortex are particularly sensitive to the envelope and can phase-lock to stimuli with complex temporal and spectrotemporal envelopes