In the study, five epilepsy surgery patients were presented with images of famous speakers (U.S. presidents Barack Obama, George W. Bush, and Bill Clinton) or clips of their voices and asked to identify the portrait/speaker.
Voice and face processing occur through convergent neural systems that facilitate speaker recognition. Neuroimaging studies suggest that familiar voice processing engages early visual cortex, including the bilateral fusiform gyri (FG) on the basal temporal lobe. However, what role the FG plays in familiar voice processing and whether it is driven by bottom-up or top-down mechanisms is unresolved. Rhone et al. directly examined neural responses to familiar voices and faces in human FG using direct cortical recordings in epilepsy surgery patients. They tested the hypothesis that neural populations in human FG respond to familiar voices and investigated the temporal properties of voice responses in FG. Image credit: Gerd Altmann.
“From behavioral research, we know that people can identify a familiar voice faster and more accurately when they can associate it with the speaker’s face, but we never had a good explanation of why that happens,” said Dr. Taylor Abel, a researcher at the University of Pittsburgh School of Medicine.
“In the visual cortex, specifically in the part that typically processes faces, we also see electrical activity in response to famous people’s voices, highlighting how deeply the two systems are interlinked.”
Even though the interplay between the auditory and the visual brain processing systems has been widely acknowledged and investigated by various teams of neuroscientists all over the world, those systems were traditionally thought to be structurally and spatially distinct.
Until recently, few studies attempted to directly measure activity from the brain center — the primary role of which is to consolidate and process visual information — to determine whether this center is also engaged when participants are exposed to famous voice stimuli.
Dr. Abel and colleagues had a unique opportunity to study that interaction in patients with epilepsy who, as part of their medical care, were temporarily implanted with electrodes measuring brain activity to determine the source of their seizures.
Five adult patients consented to participate in the study, where the authors showed participants photographs of three U.S. presidents — Bill Clinton, George W. Bush and Barack Obama — or played short recordings of their voices, and asked participants to identify them.
The recordings of the electrical activity from the region of the brain responsible for processing visual cues — called the fusiform gyri — showed that the same region became active when participants heard familiar voices, though that response was lower in magnitude and slightly delayed.
“This is important because it shows that auditory and visual areas interact very early when we identify people, and that they don’t work in isolation,” Dr. Abel said.
“In addition to enriching our understanding of the basic functioning of the brain, our study explains the mechanisms behind disorders where voice or face recognition is compromised, such as in some dementias or related disorders.”
The study was published in the Journal of Neurophysiology.
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Ariane E. Rhone et al. Electrocorticography reveals the dynamics of famous voice responses in human fusiform gyrus. Journal of Neurophysiology, published online December 28, 2022; doi: 10.1152/jn.00459.2022