Comparing non-native and native speech: Are L2 productions more variable?

Foreign-accented speech of second language learners is often difficult to understand for native listeners of that language. Part of this difficulty has been hypothesized to be caused by increased within-category variability of non-native speech. However, until recently, there have been few direct tests for this hypothesis. The realization of vowels and word-final stops in productions of native-English L1 speakers and native-Mandarin speakers of L2 English is compared. With the largest sample size to date, it is shown that at least proficient non-native speakers exhibit little or no difference in category variability compared to native speakers. This is shown while correcting for the effects of phonetic context. The same non-native speakers show substantial deviations from native speech in the central tendencies (means) of categories, as well as in the correlations among cues they produce. This relativizes a common and a priori plausible assumption that competition between first and second language representations necessarily leads to increased variability-or, equivalently, decreased precision, consistency, and stability-of non-native speech. Instead, effects of non-nativeness on category variability are category- and cue-specific.