A recent study indicates that the brain’s auditory cortex maintains a consistent processing speed when interpreting speech, irrespective of how quickly or slowly the words are spoken.

The key finding, published in Nature Neuroscience, comes from research led by Sam Norman-Haignere, assistant professor at the Del Monte Institute for Neuroscience at the University of Rochester, in collaboration with Columbia University researchers.

“This was surprising.It turns out that when you slow down a word, the auditory cortex doesn’t change the time window it is processing. It’s like the auditory cortex is integrating across this fixed time scale,” says Norman-Haignere, the study’s first author.

Scientists had previously hypothesized that the brain might accelerate its processing in response to faster speech. However,this new research suggests that the auditory cortex operates on a fixed timescale.

Computational Models and Brain Activity

The researchers utilized computational models to understand how the brain processes speech. These models helped them determine weather the auditory cortex integrates facts across speech structures or time.

“Rather, we’ve shown that the auditory cortex operates on a fixed, internal timescale, self-reliant of the sound’s structure.”

The study involved recording precise neural activity from epilepsy patients at NYU Langone Medical Centre, Columbia University Irving Medical Center, and University of Rochester Medical Center. Electrodes were temporarily implanted in the patients’ brains to monitor seizure activity, allowing researchers to measure neural responses with high precision.

Participants listened to audiobook passages at both normal and slower speeds. The researchers expected to see changes in the neural time window based on the speech speed,but the observed differences were minimal. This suggests that the fundamental unit of processing is physical time, such as 100 milliseconds, rather than speech structures like words.

Implications for Understanding Speech Processing

nima Mesgarani, a senior author of the study and an associate professor of Electrical Engineering at Columbia, explained the meaning of the findings: “Instead, we’ve shown that the auditory cortex operates on a fixed, internal timescale, independent of the sound’s structure. This provides a consistently timed stream of information that higher-order brain regions must than interpret to derive linguistic meaning.”

According to Norman-Haignere, a better understanding of speech processing could lead to improved treatments for speech processing deficits. “One thing that is exciting about this line of work is that there are many people who have been studying hearing, and many people who have been studying language, but your brain needs to somehow transform the sounds that reach your ear into words, phrases, and sentences. So,figuring out how the brain goes from something more sound-based to something more language-based,and how to model this transformation,is an exciting space that we’re working in.”