In our quest to understand the complex inner workings of the human brain, researchers at New York University have brought us one step closer. They have pinpointed a region of the brain exclusively devoted to processing speech, which not only provides a better understanding of the cerebral landscape, but settles a long-standing dispute concerning the brain's perception of sound.
In a report published in the journal Nature Neuroscience, researchers from NYU conducted a series of experiments in which participants listened to speech as well as a variety of "environmental" sounds, such as fireworks, ping pong, and the barking of dogs. Their goal was so see if the brain processed speech in the same manner it processed other sounds, or if there existed a separate component dedicated solely to speech.
First they had to segregate speech from language. In order to differentiate between the brain's perception of speech, which involves listening and speaking, and that of language, which involves constructing and understanding sentences, the speech components were delivered in German, which none of the participants spoke.
The researchers also wanted to ensure that the environmental sounds were delivered as simple audio cues instead of identifiable sounds, which would activate different regions of the participants' brains. So they created audio "quilts" composed of sound segments, ranging from 30 to 900 milliseconds, in which the sounds were chopped up and reordered.
The subjects' brain activity was observed via functional magnetic resonance imaging (fMRI), which highlights regions of the brain that are activated by various stimuli. The tests showed expected activity in the subjects' temporal lobes, which contain the auditory cortex used to process all types of sounds. But when the participants were subjected to speech sounds, an area located deeper in this region, known as the superior temporal sulcus (STS), was activated exclusively.
"We now know there is at least one part of the brain that specializes in the processing of speech and doesn't have a role in handling other sounds," explains David Poeppel, the paper's senior author and professor in NYU's Department of Psychology and Center for Neural Science.
The research also provides better insight into this complex region of the brain.
The STS plays a major role in human social interaction. The front portion of the sulcus is primarily involved in processing speech, while the back portion is involved in an array of tasks, such as facial recognition, perception of attractiveness, the integration of sound, motion, and visual information, and theory of mind - that all-important ability to decipher the perspectives of other people.
Understanding how the brain observes, processes, and reacts to outside stimuli provides clues to its structure, function, and ultimately, its evolution.