Phonological and phonetic contributions to Thai-naïve Mandarin and Vietnamese speakers' imitation of Thai lexical tones: Effects of memory load and stimulus variability

The present study examined how native phonological and phonetic factors in non-native speech perception (Perceptual Assimilation Model [PAM]: Best, 1995) affect non-native imitation of Thai tones by Thai-naïve Mandarin and Vietnamese participants, and how memory load and stimulus variability shift the balance between phonological versus phonetic modes (Automatic Selective Perception model [ASP]: Strange, 2011) in imitation. Although overall imitation was quite good, native phonological influences, as reflected in Categorised versus Uncategorised assimilation types in a prior perception study with the same participants (Chen, Antoniou, & Best, 2023), constrained non-native tone imitations. Residual perceptual sensitivity to phonetic differences between the target stimuli and native tones, as reflected in percent choice and goodness ratings in assimilation, also affected imitation. Effects of stimulus variability and memory load were restricted and interacted with specific tones for each participant group. Imitations were generally more accurate under low memory load, constant talker and vowel conditions, consistent with a more phonetic mode of perception. Imitation accuracy decreased under high memory load, variable talker and vowel conditions, consistent with a more phonological mode of perception. Results support the PAM and ASP accounts of native phonological and phonetic effects in non-native perception and extend them to non-native tone imitation.