DOCTORAL DISSERTATION RESEARCH: Hemispheric Specialization of the Processing of Linguistic Pitch Contrasts

University Of Texas At Austin, Austin TX

Investigators

Abstract

Research studies have shown that the two hemispheres of the brain have different functions. For example, the left hemisphere has been argued to specialize language processing while artistic/creative abilities are specialized by the right hemisphere. This dissertation will evaluate two possible accounts for hemispheric specialization of pitch processing. The first account is a functional account which states that hemispheric specialization of pitch processing is determined by the function of pitch contrasts. For example, pitch contrasts that are more linguistic (e.g. linguistic tone, stress, and intonation) are processed by the left hemisphere, and pitch contrasts that are less linguistic (e.g. music) are processed by the right hemisphere. The second account is an acoustic account which states that acoustic correlates determine hemispheric specialization, and therefore, all processing of pitch, regardless of function, is carried out by one hemisphere of the brain. Thus, pitch used in both intonation and music might be processed by the right hemisphere or the left hemisphere. Three sets of experiments involving the perception of linguistic tone (or linguistic pitch contrast) will be conducted in order to evaluate these two accounts. Linguistic tone is defined as pitch pattern that is used to signal meaning at the word level (e.g. in Chinese, /ma/ spoken with a high pitch means 'mother'; the same syllable means 'a horse' when spoken with a falling pitch). The first experiment will use brain-damaged individuals as subjects; patients with either left-hemisphere or right-hemisphere damage will be asked to identify linguistic tones. The second experiment is a dichotic listening experiment which will present linguistic tones to only one ear of normal-hearing subjects and assess which ear/hemisphere combination better detects these tones. The third experiment will use neuroimaging technique to examine directly which cerebral hemisphere is active when normal-hearing subjects are listening to linguistic tones. Most languages of the world (although not English) utilize linguistic tones. A better understanding of how the brain processes linguistic tones will not only help us to understand language processing and the universality of language, but may also help us to develop therapeutic techniques to help rehabilitate the oral communication skills of many brain damaged patients.