Asymmetries in Perceptual Adjustments to Non-Canonical Pronunciations

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.

Eye Gaze and Perceptual Adaptation to Audiovisual Degraded Speech

Purpose Visual cues from a speaker's face may benefit perceptual adaptation to degraded speech, but current evidence is limited. We aimed to replicate results from previous studies to establish the extent to which visual speech cues can lead to greater adaptation over time, extending existing results to a real-time adaptation paradigm (i.e., without a separate training period). A second aim was to investigate whether eye gaze patterns toward the speaker's mouth were related to better perception, hypothesizing that listeners who looked more at the speaker's mouth would show greater adaptation. Method A group of listeners ( n = 30) was presented with 90 noise-vocoded sentences in audiovisual format, whereas a control group ( n = 29) was presented with the audio signal only. Recognition accuracy was measured throughout and eye tracking was used to measure fixations toward the speaker's eyes and mouth in the audiovisual group. Results Previous studies were partially replicated: The audiovisual group had better recognition throughout and adapted slightly more rapidly, but both groups showed an equal amount of improvement overall. Longer fixations on the speaker's mouth in the audiovisual group were related to better overall accuracy. An exploratory analysis further demonstrated that the duration of fixations to the speaker's mouth decreased over time. Conclusions The results suggest that visual cues may not benefit adaptation to degraded speech as much as previously thought. Longer fixations on a speaker's mouth may play a role in successfully decoding visual speech cues; however, this will need to be confirmed in future research to fully understand how patterns of eye gaze are related to audiovisual speech recognition. All materials, data, and code are available at https://osf.io/2wqkf/ .

Electrophysiological correlates of perceptual prediction error are attenuated in dyslexia

A perceptual adaptation deficit often accompanies reading difficulty in dyslexia, manifesting in poor perceptual learning of consistent stimuli and reduced neurophysiological adaptation to stimulus repetition. However, it is not known how adaptation deficits relate to differences in feedforward or feedback processes in the brain. Here we used electroencephalography (EEG) to interrogate the feedforward and feedback contributions to neural adaptation as adults with and without dyslexia viewed pairs of faces and words in a paradigm that manipulated whether there was a high probability of stimulus repetition versus a high probability of stimulus change. We measured three neural dependent variables: expectation (the difference between prestimulus EEG power with and without the expectation of stimulus repetition), feedforward repetition (the difference between event-related potentials (ERPs) evoked by an expected change and an unexpected repetition), and feedback-mediated prediction error (the difference between ERPs evoked by an unexpected change and an expected repetition). Expectation significantly modulated prestimulus theta- and alpha-band EEG in both groups. Unexpected repetitions of words, but not faces, also led to significant feedforward repetition effects in the ERPs of both groups. However, neural prediction error when an unexpected change occurred instead of an expected repetition was significantly weaker in dyslexia than the control group for both faces and words. These results suggest that the neural and perceptual adaptation deficits observed in dyslexia reflect the failure to effectively integrate perceptual predictions with feedforward sensory processing. In addition to reducing perceptual efficiency, the attenuation of neural prediction error signals would also be deleterious to the wide range of perceptual and procedural learning abilities that are critical for developing accurate and fluent reading skills.

Rapid cross-sensory adaptation of self-motion perception

Perceptual adaptation is often studied within a single sense. However, our experience of the world is naturally multisensory. Here, we investigated cross-sensory (visual vestibular) adaptation of self motion perception. It was previously found that relatively long visual self-motion stimuli (greater or equal to 15s) are required to adapt subsequent vestibular perception, and that shorter duration stimuli do not elicit cross sensory (visual vestibular) adaptation. However, it is not known whether several discrete short duration stimuli may lead to cross sensory adaptation (even when their sum, if presented together, would be too short to elicit cross sensory adaptation). This would suggest that the brain monitors and adapts to supra modal statistics of events in the environment. Here we investigated whether cross sensory (visual vestibular) adaptation occurs after experiencing several short (1s) self-motion stimuli. Forty five participants discriminated the headings of a series of self motion stimuli. To expose adaptation effects, the trials were grouped in 140 batches, each comprising three prior trials, with headings biased to the right or left, followed by a single unbiased test trial. Right, and left biased batches were interleaved pseudo randomly. We found significant adaptation in both cross sensory conditions (visual prior and vestibular test trials, and vice versa), as well as both unisensory conditions (when prior and test trials were of the same modality, either visual or vestibular). Fitting the data with a logistic regression model revealed that adaptation was elicited by the prior stimuli (not prior choices). These results suggest that the brain monitors supra modal statistics of events in the environment, even for short duration stimuli, leading to functional (supra modal) adaptation of perception.

Speech-specific perceptual adaptation deficits in children and adults with dyslexia

According to several influential theoretical frameworks, phonological deficits in dyslexia result from reduced sensitivity to acoustic cues that are essential for the development of robust phonemic representations. Some accounts suggest that these deficits arise from impairments in rapid auditory adaptation processes that are either speech-specific or domain-general. Here, we examined the specificity of auditory adaptation deficits in dyslexia using a non-linguistic tone anchoring (adaptation) task and a linguistic selective adaptation task in children and adults with and without dyslexia. Children and adults with dyslexia had elevated tone-frequency discrimination thresholds, but both groups benefitted from anchoring to repeated stimuli to the same extent as typical readers. Additionally, although both dyslexia groups had overall reduced accuracy for speech sound identification, only the child group had reduced categorical perception for speech. Across both age groups, individuals with dyslexia had reduced perceptual adaptation to speech. These results highlight broad auditory perceptual deficits across development in individuals with dyslexia for both linguistic and non-linguistic domains, but speech-specific adaptation deficits. Finally, mediation models in children and adults revealed that the causal pathways from basic perception and adaptation to phonological awareness through speech categorization were not significant. Thus, rather than having causal effects, perceptual deficits may co-occur with the phonological deficits in dyslexia across development.

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.