New brain mechanism identified for interpreting speech

December 19, 2007

In conversation, humans recognize words primarily from the sounds they hear. However, scientists have long known that what humans perceive goes beyond the sounds and even the sights of speech. The brain actually constructs its own unique interpretation, factoring in both the sights and sounds of speech.

For example, when combining the acoustic patterns of speech with the visual images of the speaker's mouth moving, humans sometimes reconstruct a syllable that is not physically present in either sight or sound. Although this illusion suggests spoken syllables are represented in the brain in a way that is more abstract than the physical patterns of speech, scientists haven't understood how the brain generates abstractions of this sort.

In a study published in the December 20th issue of Neuron, researchers at the University of Chicago identify brain areas responsible for this perception. One of these areas, known as Broca's region, is typically thought of as an area of the brain used for talking rather than listening.

"When the speech sounds do not correspond exactly to the words that are mouthed, the brain often conjures a third sound as an experience - and this experience may often vary from what was actually spoken," explains Uri Hasson, lead author of the study and a post-doctoral scholar at the university's Human Neuroscience Laboratory.

"As an example, what would happen if a person's voice says 'pa,' but the person's lips mouth the word 'ka"' One would think you might hear 'pa' because that is what was said. But in fact, with the conflicting verbal and visual signals, the brain is far more likely to hear 'ta,' an entirely new sound," he explains.

This demonstration is called the McGurk effect (named after Harry McGurk, a developmental psychologist from England who first noticed this phenomenon in the 1970s). In the current study, scientists used functional magnetic resonance imaging (graphic depiction of brain activity) to demonstrate that Broca's region is responsible for the type of abstract speech processing that underlies this effect.

Although we experience speech as a series of words like print on a page, the speech signal is not as clear as print, and must be interpreted rather than simply recognized, Hasson explains.

He says this paper provides a glimpse into how such interpretations are carried out in the brain. These types of interpretations might be particularly important, when the speech sounds are unclear, such as when conversing in a crowded bar, listening to an unfamiliar accent, or coping with hearing loss. "In all these cases, understanding what is said requires interpreting the physical speech signal to determine what is said. And scientists now know the Broca's region is plays a major role in this process."
The National Institute of Mental Health supported this research (#R01-DC03378). Additional authors include Jeremy Skipper, Howard Nusbaum and Steven Small of the University of Chicago.

University of Chicago Medical Center

Related Brain Articles from Brightsurf:

Glioblastoma nanomedicine crosses into brain in mice, eradicates recurring brain cancer
A new synthetic protein nanoparticle capable of slipping past the nearly impermeable blood-brain barrier in mice could deliver cancer-killing drugs directly to malignant brain tumors, new research from the University of Michigan shows.

Children with asymptomatic brain bleeds as newborns show normal brain development at age 2
A study by UNC researchers finds that neurodevelopmental scores and gray matter volumes at age two years did not differ between children who had MRI-confirmed asymptomatic subdural hemorrhages when they were neonates, compared to children with no history of subdural hemorrhage.

New model of human brain 'conversations' could inform research on brain disease, cognition
A team of Indiana University neuroscientists has built a new model of human brain networks that sheds light on how the brain functions.

Human brain size gene triggers bigger brain in monkeys
Dresden and Japanese researchers show that a human-specific gene causes a larger neocortex in the common marmoset, a non-human primate.

Unique insight into development of the human brain: Model of the early embryonic brain
Stem cell researchers from the University of Copenhagen have designed a model of an early embryonic brain.

An optical brain-to-brain interface supports information exchange for locomotion control
Chinese researchers established an optical BtBI that supports rapid information transmission for precise locomotion control, thus providing a proof-of-principle demonstration of fast BtBI for real-time behavioral control.

Transplanting human nerve cells into a mouse brain reveals how they wire into brain circuits
A team of researchers led by Pierre Vanderhaeghen and Vincent Bonin (VIB-KU Leuven, Université libre de Bruxelles and NERF) showed how human nerve cells can develop at their own pace, and form highly precise connections with the surrounding mouse brain cells.

Brain scans reveal how the human brain compensates when one hemisphere is removed
Researchers studying six adults who had one of their brain hemispheres removed during childhood to reduce epileptic seizures found that the remaining half of the brain formed unusually strong connections between different functional brain networks, which potentially help the body to function as if the brain were intact.

Alcohol byproduct contributes to brain chemistry changes in specific brain regions
Study of mouse models provides clear implications for new targets to treat alcohol use disorder and fetal alcohol syndrome.

Scientists predict the areas of the brain to stimulate transitions between different brain states
Using a computer model of the brain, Gustavo Deco, director of the Center for Brain and Cognition, and Josephine Cruzat, a member of his team, together with a group of international collaborators, have developed an innovative method published in Proceedings of the National Academy of Sciences on Sept.

Read More: Brain News and Brain Current Events is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to