Preattentive Extraction Of Abstract Auditory Rules:a Study Using Chinese Lexical Tones

Encoding of abstract rules, an abstract representation of knowledge in memory, is a critical cognitive function essential for percept of the world and is a central structure in cognitive science. For biological organisms, the capacity of extraction of abstract rules from a complex environment is beneficial for survival. This capacity may particularly be important to humans for ensuring everyday speech communication because often listeners are confronted with considerable variation in intensity and spectral-temporal property of speech signals as well as ambient noise. To cope with this variability, it is necessary for the auditory cortex to process the relations between the stimuli in order to derive and form efficient abstract representations, such as speaker identity or speech content. These relations are referred to as the abstract auditory rule in speech, which has currently been under investigation for its underlying neural mechanisms at an attentive stage. However, it is not well addressed whether or not there is a sensory intelligence that enables one to unconsciously encode abstract auditory rules in speech at a preattentive stage already. In the present study, we deployed Chinese lexical tones since they define word meaning and hence facilitate the fabrication of an abstract auditory rule in speech. In this study native Chinese speakers were presented continuously with Chinese vowels differing in formant, intensity and level of pitch to construct a complex and varying auditory stream. In the stream, most of sounds shared flat lexical tones to form an embedded abstract auditory rule, and occasionally this rule was violated with random occurrence of those with rising or falling lexical tones. The results show that the violation of the abstract auditory rule of lexical tones evoked a robust preattentive auditory response, as revealed by whole-head electrical recordings of the mismatch negativity, though none of the subjects acquired explicit knowledge of the rule or became aware of the violation of the rule. The results demonstrate that there is an auditory sensory intelligence in perception of Chinese lexical tones. The existence of this intelligence indicates that the human can automatically extract abstract auditory rules in speech at a preattentive stage already to ensure speech communication in complex and noisy auditory environments without consuming much conscious resources.