The thesis investigates how native language phonological and phonetic factors affect non-native lexical tone perception and imitation, and how cognitive factors, such as memory load and stimulus variability (talker and vowel context variability), bias listeners to a phonological versus phonetic mode of perception/imitation. Two perceptual experiments and one imitation experiment were conducted with Thai tones as the stimuli and with Mandarin and Vietnamese listeners, who had no experience with Thai (i.e., naive listeners/imitators). The results of the perceptual experiments (Chapters 5 and 6) showed phonological effects as reflected in assimilation types (Categorised vs. UnCategorised assimilation) and phonetic effects indicated by percent choice and goodness ratings in tone assimilation, largely in line with predictions based on the Perceptual Assimilation Model (PAM: Best, 1995). In addition, phonological assimilation types and phonological overlap of the contrasts affected their discrimination in line with predictions based on PAM. The thesis research has revealed the influence of cognitive factors on native language influences in perception and imitation of non-native lexical tones, which contribute differently to different tasks. The findings carry implications for current non-native speech perception theories. The fact that non-native tone imitation deviations can be traced back to native phonological and phonetic influences on perception supports and provides new insights about perception-production links in processing non-native tones. The findings uphold the extrapolation of PAM and ASP principles to non-native tone perception and imitation, indicating that both native language phonological and phonetic influences and their modulation by cognitive factors hold implications for non-native speech perception/learning theories, as well as for second language instruction
