Previous work has shown that advanced Korean learners of English (L2ers) are less effective than native English speakers (L1ers) at using English intermediate phrases (ips) to establish syntactic boundaries [10]. This study investigated whether the effect is due to perceptual differences between L1ers and L2ers, based on the interplay between phonology and perception (e.g., [5], [8], [9]). L1ers and L2ers listened to pairs of phrases in an AX task that crossed boundary strength with intonational contour. Little variation was found between L1ers' and L2ers' discrimination patterns, which correlated highly with each other. Both groups were more sensitive to a falling vs. level contour contrast than a rising vs. level contrast (in the context tested) and were more responsive to contour contrasts than boundary strength contrasts. The results suggest that the L2ers' poor use of ips in comprehension likely rests primarily on difficulty with prosody-syntax mappings.