Long-Term Memory Traces For Tonal Langauge Words Revealed By Auditory Event-Related Potentials

Language is an important tool for human communication, and also an important tool for the preservation and inheritance of human civilization. The neural mechanism of language processing is an important research field, especially after the rise of modern brain research techniques invented. The cognitive neuroscience research of language could be divided into the speech perception and production, and visual language perception and production research. In the field of speech perception research, the great progress in the past two decades is the discovery of long-term memory traces for speech units in the brain, such as long-term memory traces for vowels, syllables, words and even the phrasal verbs. The rapid activation of these long-term memory traces in speech perception provides the foundation for further analysis of complex speech signals.The long-term memory traces for words in the brain was first revealed in studies using Finish words as experimental materials, verified by using English and German words. In these studies, words and acoustically (and phonologically) matched pseudo-words were presented as deviants in a passive oddball paradigm. The mismatch negativity (MMN) elicited by words were significantly larger than elicited by pseudo-words, reflected the activation of long-term memory traces for words in the brain.So far, all the studies used non-tonal language words as experimental materials. These words in non-tonal languages are all composed of segmental phonemes, without any composition of suprasegmental phonemes. However, the vast majority of the world’s languages are tonal. In these tonal languages, the fundamental frequency (f0) contours of syllables can determine the word meaning beside consonants and vowels. Such f0contours are called tones. Tonal information and segmental information are parallelly existed in speech signal, and tones can extend over more than one speech segment. Therefore, tones are typical suprasegmetnal phonemes. Whether the tonal information is involved in the formation and activation of long-term memory traces for words is the question to be answered in this study.Eighteen Mandarin-speaking subjects participated in this study. They were presented with a sequence of spoken syllables ([huo4] and [kuo4], P=41.67%) as standards and disyllables ([huo4da2],[kuo4da4],[huo4da4] and [kuo4da2], P=41.67%) as deviants in a passive oddball paradigm. The second syllable of each disyllable carried critical tonal information that would define the disyllable either as a meaningful word ([huo4da2],[kuo4da4]) or as a meaningless pseudo-word ([huo4da4] and [kuo4da2]). The words and pseudo-words were acoustically and phonologically matched as well as counterbalanced. The auditory event-related potential in response to words was more negatively deflected than to pseudo-words, and this effect was most prominent at164ms after the word recognition point. This result indicates an activation of long-term memory traces for tonal language words in the brain.The results suggest that, in the process of language acquisition, the tonal information and segmental information both participate in the formation of long-term memory traces for words in the brain. Similarly, in the process of speech perception, tonal information and the segmental information both participate in the activation of the long-term memory traces for words. And the time course of activation (which peaked164ms after the word recognition point) is comparable to the results of previous non-tonal language studies (-150ms), suggesting that the neural mechanisms for early lexical processes are analogous for tonal and non-tonal languages.