THE TIME COURSE OF THE EXTRINSIC VOWEL NORMALIZATION: AN ERP STUDY

Abstract: Due to the talker variabilities, there is no one-to-one map between speech signals and the phonological categories. The extrinsic context provides listeners valuable information to overcome the speech variability and achieve the perceptual constancy. Although lots of studies show the effectiveness of speech context in normalizing vowels, consonants, and lexical tones, the cognitive mechanism underlying the extrinsic normalization remains largely unknown. Speech perception consists of multiple stages, ranging from acoustic, phonetic, and phonological processes to the semantic, syntactic and pragmatic processes. It is still a controversial question that at which stage(s) the extrinsic normalization occurs. To clarify this question, the present study recorded the electroencephalographic (EEG) signals when listeners perceived vowels in different contexts. The high temporal resolution of the EEG technique allows us to probe the precise time course of the cognitive process of extrinsic vowel normalization. The EEG results suggested that the extrinsic normalization of vowels probably occurs at P2 time window, i.e., at around 130 ms to 250 ms after the vowel onset. Considering that P2 is related to the phonological processing, the extrinsic vowel normalization is probably realized in the phonological process.