Researchers at the University of Pittsburgh have found that certain parts of the brain recognize complex signals in human vocal sounds that do not involve speech, such as crying, coughing or breathing.
In an article published today in PLOS Biology, scientists have shown that two areas of the auditory cortex specialize in recognizing the sounds of the human voice, which, unlike speech, do not carry linguistic meaning. Rather, they help us respond to audio cues that allow people to instantly identify a speaker’s characteristics, such as gender, approximate age, mood, and even height—all without seeing them.
“Voice perception is similar to how people recognize different faces,” said senior author Taylor Abel, MD, assistant professor of neurosurgery at Pitt. “Voices that do not involve speech — such as babies crying, coughing, moaning or exclamations — allow us to get a lot of information about the person making these vocalizations in the absence of other information about the person.”
Humans live in a world full of sounds, where environmental noises define our daily interactions with our environment and other people. And although speech is one of the unique aspects of human communication that has no direct counterpart in the animal world, humans do not rely solely on speech to convey auditory information.
The non-verbal aspects of the voice play a vital role in our communication toolkit, enhancing the human ability to express ourselves clearly and dynamically. Some of this expression is subconscious, and some may be intentionally modulated by the speaker to convey a wide range of emotions, such as happiness, fear, or disgust.
Humans are born with the ability to recognize voice – in fact, babies can recognize their mother’s voice even in the womb – but this ability is dynamic and continues to develop throughout adolescence.
Abel, who is a practicing pediatric neurosurgeon specializing in epilepsy, had the unique opportunity to observe how the human brain responds to voice.
To identify the areas of the brain responsible for seizures in some people with epilepsy, neurosurgeons can implant temporary electrodes in the brain to carefully record its electrical signals. This practice allows doctors to pinpoint the location of the seizure and ultimately remove that part of the brain while sparing the surrounding healthy tissue.
Eight epilepsy patients consented to participate in a study in which Abel and his team used implanted electrodes to measure which areas of the auditory cortex responded to vocal sounds — grunts, yelps, laughs — given to the patients.
Using a combination of direct brain recordings and computational modeling, the researchers were able to describe in unprecedented detail how vocal representation develops over time and decode when a vocal sound was played based on patterns of neural activity in the auditory cortex.
The researchers found that most of this activity comes from two areas of the auditory cortex — folds of the brain’s gray matter known as the superior temporal gyrus (STG) and the superior temporal sulcus (STS). While previous brain imaging studies have shown that the STG and STS are important for voice processing, this study demonstrates that these areas represent the voice as a distinct sound category rather than simply representing the physical or acoustic aspects of the voice.
This new knowledge about the organization of the voice recognition system embedded in our brain will allow researchers to better understand neurological diseases such as schizophrenia or autism, where voice perception is altered or absent, and even help create better voice assistant devices that are currently good at recognizing speech. , but is less able to distinguish between multiple carriers.
Kyle Rapp, PhD, is the paper’s lead author; additional authors: Jasmine Hecht, Madison Remick, Avniel Ghuman, PhD, and Bharat Chandrasekaran, PhD, all of Pitt; and Laurie Holt, Ph.D., Carnegie Mellon University.
This research was supported by the National Institutes of Health (grants R21DC019217-01A1 and 2R01DC013315-07).
