This is the publisher's version, also available electronically from http://scitation.aip.org/content/asa/journal/poma/18/1/10.1121/1.4798223.Many studies on L2 speech learning focused on testing the L1 transfer hypothesis. In general, L2 phonemes were found to be merged with similar L1 phoneme to different degrees (Flege 1995). Few studies examined whether non-phonemic phonetic categories in L1 help or block the formation of new phonetic categories in L2. The current study examined the effect of L1 English consonantal clusters [ts] and [dz] on learning L2 Chinese affricates /ts/ and /tsh/. We studied duration and center of gravity (COG) of Chinese affricates /ts/ and /tsh/ produced by native Chinese speakers, novice American Chinese learners and advanced learners. In terms of duration, both learner groups showed contrast between L2 /ts/ and /tsh/, which is similar to native Chinese speakers' production. However, for COG, only the advanced learner group showed contrast between L2 /ts/ and /tsh/, which is similar to native speakers' production while the novice learner group did not show a COG difference between the two L2 affricates. The results suggest an early acquisition of the durational contrast between the L2 Chinese affricates and later acquisition of COG contrast between the two L2 affricates
