Very Early Cortical Auditory Responses to Speech in Humans
A foundational measure of the auditory systems ability to process sound correctly is the auditory brainstem response (ABR) and middle latency response (MLR) complex, but their dependence on stimulus complexity and behavioral relevance is poorly understood. Here we recorded noninvasive, simultaneous electroencephalography (EEG) and magnetoencephalography (MEG) in adults listening to both naturalistic speech and clicks, and computed the resulting temporal response functions (TRFs). The TRFs ABR-MLR complex for speech listening contains a very early cortical peak (11 ms latency), which has not been well-characterized, and is absent for click stimuli. Other significant differences in latency and source between the speech and click MLR complexes point to further differences in their auditory processing, in thalamus and cortex. In contrast, the speech and click TRFs ABR complex both share a similar, prominent wave V response. In summation, the use of naturalistic speech reveals how early auditory responses reflect its ethological relevance.