Research Update
Tuned in to the human voice
CMAJ 2000;162:1034
Human beings have a wonderful ability to recognize voices, even voices they haven't heard for years, and they can easily and accurately interpret a great deal of information about people from their voices, including sex, approximate age and emotional state. But little is known about the way the brain performs these neuronal feats.
Cognitive neuroscientist Pascal Belin has identified several regions of the superior temporal sulcus (STS) that are activated by the human voice (Nature 2000;403:307-12). Using functional magnetic resonance imaging, Belin and colleagues at the Montreal Neurological Institute demonstrated that areas of this deep fissure of the temporal lobe are much more active when test subjects listen to human voices than to other sounds. "This study increases our knowledge of the auditory cortex," says Belin, adding that the function of the STS was unknown until now. "It also draws an important parallel with face perception, because the voice is the face of the auditory system. Research on face perception is a hot topic now, and I think this discovery will stimulate a similar amount of research into the organization of the auditory brain."
Sixteen normal adult men and women were scanned during silence or while listening passively to various stimuli. Vocal stimuli included not only words and sentences in different languages, but also nonspeech vocalizations such as laughter, sighs and coughs. Nonvocal stimuli included animal cries and natural and mechanical noises. Scanning showed that the voice-selective regions found bilaterally along the upper bank of the STS showed greater neuronal activity when subjects listened to vocal sounds than to nonvocal sounds.
In a second part of the experiment, the subjects listened to control sounds of human origin such as finger snaps and to scrambled and filtered vocal sounds in order to characterize the response of the voice-sensitive regions to modifications of the acoustic structure of voice. "This allowed us to demonstrate that the 'voice area' is really selectively activated by voice, and is not simply responding to particular acoustic components that might be found in other sounds as well," says Belin.
This research might help increase understanding of how the human brain evolved, he suggests. "Whereas speech is unique to humans, the ability to perceive the voice and analyse the sounds made by other members of the same species is something we share with a lot of other animals, and it is likely that voice-selective areas exist in the brains of closely related primates." — Janice Hamilton, Montreal
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