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.

中文翻译：

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比较非本地语言和母语：L2产生的变量是否更多？

第二语言学习者的外国口音通常很难被该语言的母语听众理解。据推测，这种困难的部分原因是由于非母语语音的类别内变异性增加所致。但是，直到最近，才对该假设进行了直接检验。比较母语为L1的英语母语者和母语为L2的英语的普通话群体的发音中的元音和字词最终音的实现。迄今为止最大的样本量表明，与母语使用者相比，至少熟练的非母语使用者在类别变异性方面几乎没有差异。在校正语音环境的影响时会显示此内容。相同的非母语使用者在类别的中心趋势（均值）中与母语的语音存在很大差异，以及它们产生的线索之间的相关性。这使相对论和一种先验的合理假设，即第一和第二种语言表示形式之间的竞争必然会导致非本地语音的可变性增加，或者等效地，降低其精度，一致性和稳定性。相反，非本地性对类别可变性的影响是特定于类别和提示的。