High-level neural categorization of human voices as revealed by fast periodic auditory stimulation

Abstract

Voices are arguably among the most relevant sounds in humans' everyday life and several studies have demonstrated the existence of voice-selective regions in the human brain. However, whether this preference is merely driven by physical (i.e., acoustic) properties specific to voices, or whether it reflects a higher-level categorical response is still under debate. Here, we address this fundamental issue with Fast Periodic Auditory Stimulation combined with electroencephalography (EEG) to measure objective, direct, fast and automatic voice- selective responses in the human brain. Participants were tested with stimulation sequences containing heterogeneous non-vocal sounds from different categories presented at 4 Hz (i.e., 4 stimuli/second), with vocal sounds appearing every 3 stimuli (1.33 Hz). A few minutes of stimulation are sufficient to elicit robust 1.33 Hz voice-selective focal brain responses over superior temporal regions of individual participants. This response is virtually absent for sequences using frequency-scrambled sounds, but is clearly observed when voices are inserted in sounds from musical instruments matched in pitch and harmonicity-to-noise ratio. Overall, our Fast Periodic Auditory Stimulation paradigm demonstrates high-level categorization of human voices, and could be a powerful and versatile tool to understand human auditory categorization in general