Examining the Effect of Assimilation Overlap on Discrimination of English and Persian Stop–Fricative Contrasts in Chinese Listeners

Research on cross-language adult speech perception shows that non-native speech sounds are interpreted through the listener’s L1 phonological system. According to the Perceptual Assimilation Model (PAM) and its extension, PAM-L2, discriminability of non-native/L2 speech contrasts is determined by how two phones are assimilated to L1 phonological categories. Specifically, discriminability varies depending on perceived overlap with L1 phonological categories. This study assessed the PAM/PAM-L2 account of the assimilation–discrimination relationship in discrimination of non-native/L2 stop–fricative contrasts, focusing on how discrimination varies with assimilation overlap. Chinese listeners completed assimilation and AXB discrimination tasks with six English (/p-f/, /b-v/, /t-θ/, /t-s/, /d-ð/, /d-z/) and two Persian (/k-x/, /g-ɣ/) stop–fricative contrasts. The contrasts were assimilated as four Uncategorized–Categorized (UC) contrasts, one with no overlap and three with partial overlap, and four Two-Category (TC) contrasts. The discrimination results showed that TC and non-overlapping UC contrasts were more accurately discriminated than partially overlapping UC contrasts, consistent with PAM/PAM-L2. Further analysis revealed that overlap scores were strongly negatively correlated with discrimination accuracy at the group level, and this correlation was also significant for most contrasts at the individual level. These findings suggest that exploring assimilation overlap may help clarify the assimilation–discrimination relationship in non-native/L2 stop–fricative contrast discrimination.