This study reports an experiment in which native speakers of Chinese, Japanese, and Vietnamese performed an identification task with English voiceless obstruents. Although these three languages resemble English in distinguishing alveolar from post-alveolar fricatives, they all differ in their phonetic implementation of the post-alveolar. We investigate the impact the different realizations have on categorical perception, as well as the ramifications of phonological neutralization, allophonic alternation, and invariant contrast in each of these languages. Results indicate differences in identification performance based on native language that reflect the mapping between phonological categories and phonetic realizations in addition to the phonological behavior of these segments in different vowel environments in each language.