Asymmetries in Perceptual Adjustments to Non-Canonical Pronunciations

Listeners need to accommodate pronunciations that vary widely. Lexically-guided perceptual adaptation has been well documented in the literature, but relatively little is known about its limits. Moreover, there are at least two plausible mechanisms supporting adaptation for sound categories: targeted shifts towards the novel pronunciation or a general relaxation of criteria. This paper examines a limit of perceptual adaptation — asymmetries in adaptation to the voicing and devoicing of coronal fricatives in English — and suggests that typology or synchronic experience affects how listeners adapt. A corpus study of coronal fricative substitution patterns confirmed that North American English listeners are more likely to be exposed to devoiced /z/ than voiced /s/. Across two perceptual adaptation experiments, listeners in test conditions head naturally produced devoiced /z/ or voiced /s/ in critical items within sentences, while control listeners were exposed to identical sentences with canonical fricative pronunciations. Perceptual adaptation was tested via word endorsement rates in a lexical decision test, with devoiced /z/ or voiced /s/, as well as a novel alveopalatalized pronunciation, to determine whether adaptation was targeted in the direction of the exposed variant or reflected more general relaxation. Results indicate there was targeted and word-specific adaptation for /z/ devoicing. Conversely, there was some evidence of /s/ voicing eliciting a more general category relaxation. These results underscore the role of prior perceptual experiences, and suggest a need for an evaluation stage in lexically-guided perceptual learning, where listeners assess whether a heard item merits an update to the representation.