Role of superior temporal gyrus and planum temporale in talker segregation

Recent studies suggest the brain tracks both attended and unattended speech streams. Here, we describe the cortical mechanisms that support active talker segregation by vocal gender. Thirty-three participants with normal or near-normal hearing performed a competing speech task during fMRI scanning. The target (competing) talker was female (male). Spectrotemporal modulation filtering was applied to stochastically modulate female and male vocal pitch across trials. Using the modulation-filter patterns as predictors, spectrotemporal receptive fields (STRFs) were obtained at each voxel using coordinate descent. STRF weights associated with female- (∼6 cyc/kHz) and male-talker (∼12 cyc/kHz) pitch were analyzed across subjects to identify pitch-sensitive voxels (logical OR, corrected p < 0.01), which were then characterized by preference for female vs. male. Anterior regions in Heschl’s gyrus and the superior temporal gyrus (STG) responded best to the female talker, while posterior regions in STG and planum temporale (PT) responded best to the male talker. In a control task where the talkers did not compete, the same pattern was observed but the posterior network shifted from STG to PT and responded to the acoustic boundary between talkers (∼9 cyc/kHz), suggesting that acoustically coded pitch in PT becomes voice-coded in STG during active segregation.