Nasals are cross-linguistically susceptible to change, especially in the syllable final position. Acoustic reports on Mandarin nasal production have recently shown that the syllable-final distinction is frequently dropped. Few studies, however, have addressed the issue of perceptual processing in Mandarin nasals for L1 and L2 speakers of Mandarin Chinese. The current paper addressed to what extent and in what directions L1 and L2 speakers of Mandarin differed in perceiving Mandarin nasals. Possible variables, including the linguistic backgrounds (i.e. L1 vs. L2 speakers of Mandarin Chinese), the vocalic contexts (i.e. [i, [schwa], a, y, ua, u[schwa], ia]) and the phonetic settings (i.e. syllable-initial vs. syllable-final), were discussed. Asymmetrical findings in the current investigation indicated limitations of speech learning theories developed from European languages in the context of Mandarin nasals. A tri-dimensional model was thus suggested for interpreting the cognitive mechanism in Mandarin nasal perception.