This article examines how three factors determine the surface forms of English stop-stop coarticulation across word boundaries in both native and nonnative speech: place of articulation, frequency, and speech rate. The release percentage and closure duration ratio produced by English (L1) and Mandarin (L2) speakers were measured. The results showed that a place order effect was only partially supported in L1 speech but not shown at all in L2 speech. The results also confirmed a gradient lexical effect, finding a significant correlation between self-rated frequency and overlap. In addition, the results showed that increased speech rate did not induce increased overlap, given that speakers from both groups had either more or less overlap at the fast speech rate than at the slow rate.
