February 18, 2008

Pitch Patterns Play Greater Role in Speech Perception

MONDAY, Feb. 18 (HealthDay News) -- The pitch of language and sound affects the development of the brain more than previously thought, according to new research.

"Everyone has a brain stem, but it's tuned differently depending on what sounds are behaviorally relevant to a person, for example, the sounds of his or her mother tongue," Jackson T. Gandour, a linguistics professor at Purdue University, said in a prepared statement.

Gandour was to present several of his pitch-processing studies Saturday during the American Association for Advancement of Science's annual meeting, in Boston.

One set of findings comes from a collaboration comparing brain activity in young adult speakers of the tonal language Mandarin with those of speakers of English, a non-tonal language.

Tone languages use inflections of pitch on syllables to indicate a difference between words. For example, in Mandarin the sound "ma" with a level tone means "mother," a rising tone means "hemp," a falling-rising tone means "horse" and a falling tone means "scold."

"By studying brain activity at different stages of processing pitch patterns in tonal languages, we have found that early activity in the brain stem is shaped by a person's language experience, even while the person is asleep, and consequently, we now believe it plays a much greater role in speech perception than we thought before," Gandour said.

The brain stem is located early along the auditory pathway, just 7 to 9 milliseconds from the time the auditory signal enters the ear. This is also near where pitch processing begins in the cochlea and the auditory nerve.

"Never did I expect we would find that language experience would shape the way the brain stem works," Gandour said. "The idea is that this sensory signal undergoes a set of transformations that are far more complicated than we originally thought."

Another study looking at blood flow in the cerebral cortex revealed that the melody of speech is processed in neither a single region nor a specific hemisphere. Instead, it engages multiple areas of the brain comprising large-scale networks that involve both hemispheres.

"And moreover, we find that these networks are not circumscribed to language processes but instead interact with more general sensory-motor and cognitive process in addition to those associated with language," he said.

The findings show that when the melody of speech is processed, a dynamic interplay between the left and right hemispheres of the brain occurs. The processing pitch of information engages neural mechanisms in the brain's right hemisphere, while left hemisphere regions mediate processing of linguistic information, he said.

More information

The National Institute on Aging has more about how the brain works.

-- Kevin McKeever
SOURCE: Purdue University, news release, Feb. 16, 2008
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