This study examined the effect of native language background on listeners' perception of native and non-native vowels spoken by native (Hong Kong Cantonese) and non-native (Mandarin and Australian English) speakers. They completed discrimination and an identification task with and without visual cues in clear and noisy conditions. Results indicated that visual cues did not facilitate perception, and performance was better in clear than in noisy conditions. More importantly, the Cantonese talker's vowels were the easiest to discriminate, and the Mandarin talker's vowels were as intelligible as the native talkers' speech. These results supported the interlanguage speech native intelligibility benefit patterns proposed by Hayes-Harb et al. ("J Phonetics" 36:664-679, 2008). The Mandarin and English listeners' identification patterns were similar to those of the Cantonese listeners, suggesting that they might have assimilated Cantonese vowels to their closest native vowels. In addition, listeners' perceptual patterns were consistent with the principles of Best's Perceptual Assimilation Model ("Best in Speech perception and linguistic experience: issues in cross-language research." York Press, Timonium, 1995).