Very Early Cortical Auditory Responses to Speech in Humans

A foundational measure of the auditory system's ability to process sound correctly is the auditory brainstem response (ABR) and middle latency response (MLR) complex, but how they vary with stimulus complexity and behavioral relevance is not well understood. To address these issues, we recorded noninvasive electromagnetic temporal response functions (TRFs) in healthy, young adults listening to both clicks and naturalistic speech. Through a source analysis of the responses, we found that the TRF's ABR-MLR complex for speech listening contains a very early cortical peak (11 ms latency) which has not been previously well-characterized, and which is not present in the TRF's ABR-MLR complex for click stimuli. Several other significant differences in latency and source between the speech and click MLR complexes were found, enriching our understanding of the human auditory system's behavior for diverse stimulus types. In this way, the use of naturalistic speech coupled with the TRF framework reveals how auditory responses reflect the ethological relevance of speech at even short time scales.