Using a visual world eye-tracking paradigm, we investigated the real-time auditory sentence processing of neurologically unimpaired listeners and individuals with aphasia. We examined whether lexical-semantic cues provided as adjectives of a target noun modulate the encoding and retrieval dynamics of a noun phrase during the processing of complex, non-canonical sentences. We hypothesized that the real-time processing pattern of sentences containing a semantically biased lexical cue (e.g., the venomous snake) would be different than sentences containing unbiased adjectives (e.g., the voracious snake). More specifically, we predicted that the presence of a biased lexical cue would facilitate (1) lexical encoding (i.e., boosted lexical access) of the target noun, snake, and (2) on-time syntactic retrieval or dependency linking (i.e., increasing the probability of on-time lexical retrieval at post-verb gap site) for both groups. For unimpaired listeners, results revealed a difference in the time course of gaze trajectories to the target noun (snake) during lexical encoding and syntactic retrieval in the biased compared to the unbiased condition. In contrast, for the aphasia group, the presence of biased adjectives did not affect the time course of processing the target noun. Yet, at the post-verb gap site, the presence of a semantically biased adjective influenced syntactic re-activation. Our results extend the cue-based parsing model by offering new and valuable insights into the processes underlying sentence comprehension of individuals with aphasia.

This paper examines two plausible mechanisms supporting sound category adaptation: directional shifts towards the novel pronunciation or a general category relaxation of criteria. Focusing on asymmetries in adaptation to the voicing patterns of English coronal fricatives, we suggest that typology or synchronic experience affect adaptation. 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 heard naturally produced devoiced /z/ or voiced /s/ in critical items within sentences, while control listeners were exposed to identical sentences with canonical pronunciations. Perceptual adaptation was tested via 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 a more general relaxation. Results indicate there was directional and word-specific adaptation for /z/-devoicing with no evidence for generalization. Conversely, there was evidence of /s/-voicing generalizing and eliciting general category relaxation. These results underscore the role of perceptual experiences, and support an evaluation stage in perceptual learning, where listeners assess whether to update a representation.

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.