We present the results from an experiment that tests the perception of English consonantal sequences by Korean speakers and we confirm that perceptual epenthesis in a second language (L2) arises from syllable structure restrictions of the first language (L1), rather than linear co-occurrence restrictions. Our study replicates and extends Dupoux, Kakehi, Hirose, Pallier, & Mehler's (1999) results that suggested that listeners perceive epenthetic vowels within consonantal sequences that violate the phonotactics of their L1. Korean employs at least two kinds of phonotactic restrictions: (i) syllable structure restrictions that prohibit the occurrence of certain consonants in coda position (e.g., *[c.], *[g.]), while allowing others (e.g., [k.], [l.]), and (ii) consonantal contact restrictions that ban the co-occurrence of certain heterosyllabic consonants (e.g., *[k.m]; *[l.n]) due to various phonological processes that repair such sequences on the surface (i.e., /k.m/ [right arrow] [[engma].m]; /l.n / [right arrow] [l.l]). The results suggest that Korean syllable structure restrictions, rather than consonantal contact restrictions, result in the perception of epenthetic vowels. Furthermore, the frequency of co-occurrence fails to explain the epenthesis effects in the percept of consonant clusters employed in the present study. We address questions regarding the interaction between speech perception and phonology and test the validity of Steriade's (2001 a,b) Perceptual-Mapping (P-Map) hypothesis for the Korean sonorant assimilation processes. Our results indicate that Steriade's hypothesis makes incorrect predictions about Korean phonology and that speech perception is not isomorphic to speech production. (Contains 4 figures, 7 tables, and 11 footnotes.)