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Right hemisphere influenced by speech context
Speech perception involves both hemispheres of the human brain, but not in the same way. Speech sounds vary a lot among speakers, depending on a speaker's build, age, and gender, but listeners quite easily understand them. How does the brain achieve this? The right hemisphere is more strongly influenced by speech context (which can contain clues to speaker-specific characteristics), while the left hemisphere trusts more what the ears actually hear, MPI researchers Matthias Sjerps, Holger Mitterer and James McQueen recently discovered. Their paper 'Hemispheric differences in the effects of context on vowel perception' was published last week in the journal Brain and Language.
February 3, 2012
Listeners perceive speech sounds relative to context. For example, a vowel that may sound more like the one in the word "pet" in a sentence spoken by one speaker can actually sound more like the vowel in "pit" in a sentence spoken by another speaker. It is also known that different types of auditory processing tend to be lateralized to one or the other hemisphere. So it was predicted that different types of contextual influence on vowel perception could occur over the two hemispheres. Sjerps and his colleagues tested this prediction. They presented speech targets and contexts to listeners’ right or left ears, thereby forcing the initial stages of auditory processing to be more dominant in the left or the right hemisphere.
Stronger effects in right hemisphere
It was found that vowel perception was influenced by acoustic properties of the context speech signals: vowels tended to be perceived in contrast to the information in the context. But the strength of this influence depended on laterality of target presentation. "We conclude that contrastive contextual influences on vowel perception are stronger when targets are processed predominately by the right hemisphere," Matthias Sjerps says. The researchers also found that, in the left hemisphere, contrastive effects are smaller and largely restricted to speech contexts. There is thus a division of labour in the way the two halves of the brain interpret speech sounds in context.
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