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

研究表明，大脑的两个半球有不同的功能。例如，左半球被认为专门负责语言处理，而艺术/创造能力则由右半球专门负责。本论文将评估两种可能的半球专门化音调处理的解释。第一种解释是一种功能解释，它指出音调加工的半球专门化是由音调对比的功能决定的。例如，与语言相关的音高对比（如语言语调、重音和语调）由左脑处理，而与语言相关较少的音高对比（如音乐）由右脑处理。第二个解释是声学解释，它认为声学相关决定了半球的专门化，因此，所有的音高处理，无论功能如何，都是由大脑的一个半球进行的。因此，音准和音乐中使用的音高可能由右半球处理，也可能由左半球处理。为了评估这两种说法，将进行三组涉及语言音调感知（或语言音高对比）的实验。语言语调被定义为一种音高模式，用来表示单词层面的意思（例如，在汉语中，/ma/发高音时表示“母亲”；同一个音节发低音时表示“马”）。第一个实验将使用脑损伤个体作为实验对象；左半球或右半球损伤的患者将被要求识别语言语调。第二个实验是双听实验，将语言音调只呈现给听力正常的受试者的一只耳朵，并评估哪只耳朵/半球组合能更好地检测这些音调。第三个实验将使用神经成像技术，直接检查听力正常的受试者在听语言语调时哪个大脑半球是活跃的。世界上大多数语言（尽管不是英语）都使用声调。更好地了解大脑是如何处理语言音调的，不仅有助于我们理解语言处理和语言的普遍性，而且可能有助于我们开发治疗技术，帮助许多脑损伤患者恢复口头交流技能。

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.