Cortical activity evoked by voice pitch changes: a combined fNIRS and EEG study

Numerous studies have investigated the cortical representation and time course of responses to auditory signals with and without pitch. However, little is known regarding the responses evoked by pitch changes. To study the spatial as well as temporal characteristics of cortical activity elicited by voice pitch changes, combined functional near-infrared spectroscopy (fNIRS) and electroencephalography (EEG) data were obtained from normal-hearing listeners presented with continuous vowel sequences in which the prosodic contours either varied between the individual vowels or were the same throughout. The fNIRS topographies and the EEG source reconstructions indicated additional right-hemispheric activity anterior to the primary auditory cortex and in the superior temporal sulcus for sequences with variable prosody. Additionally, the time courses of the fNIRS signals showed that activity was more sustained in response to sequences with changing prosodic contours. The EEG data revealed a similar pattern for the P2 amplitude, which was smaller during the second half for blocks with fixed prosody, whereas the P1 was consistently larger for sequences with variable prosody. Moreover, the sources of the P2, but not the P1, were lateralised to the right, suggesting that the hemispheric asymmetry in the processing of voice pitch changes develops over time.