Apparent Talker Variability and Speaking Style Similarity Can Enhance Comprehension of Novel L2-Accented Talkers

Certain studies report facilitatory effects of multiple-talker exposure on cross-talker generalization of L2-accented speech (often defined as greater comprehension of novel talkers). However, a confound exists in prior work: do multiple-talker exposure benefits stem from the greater number of talkers (numerosity) or greater phonological variability (heterogeneity)? This study examined how apparent talker variability and speaking style affect L2-accent adaptation, while keeping phonological variation as constant as possible across exposure conditions. L1-English participants transcribed sentences in noise for a single Mandarin-accented English talker in an exposure phase and a novel Mandarin-accented English speaker in a test phase (a control condition received no exposure). Although all exposure stimuli came from one speaker, half of the listeners who received exposure were led to believe that multiple talkers were present by shifting the F0 and formants of a subset of sentences. We find: (a) when the test talker produces casual speech, all critical conditions with exposure enhance generalization (i.e., greater comprehension of the test talker relative to control); (b) when the test talker produces hard-of-hearing-directed speech, there is no difference in transcription accuracy between the control and critical conditions; and (c) when the test talker produces casual speech, generalization is greatest when listeners are exposed to multiple apparent talkers, but only given speaking style similarity between exposure and test (i.e., when the exposure phase also presents casual speech). This work lends credence to numerosity accounts-given a minimal change in phonological variability, the illusion of multiple-talker exposure can facilitate cross-talker generalization of L2-accented speech.