Effects of training length on adaptation to noise-vocoded speech.

Listeners show rapid perceptual learning of acoustically degraded speech, though the amount of exposure required to maximize speech adaptation is unspecified. The current work used a single-session design to examine the length of auditory training on perceptual learning for normal hearing listeners exposed to eight-channel noise-vocoded speech. Participants completed short, medium, or long training using a two-alternative forced choice sentence identification task with feedback. To assess learning and generalization, a 40-trial pre-test and post-test transcription task was administered using trained and novel sentences. Training results showed all groups performed near ceiling with no reliable differences. For test data, we evaluated changes in transcription accuracy using separate linear mixed models for trained or novel sentences. In both models, we observed a significant improvement in transcription at post-test relative to pre-test. Critically, the three training groups did not differ in the magnitude of improvement following training. Subsequent Bayes factors analysis evaluating the test by group interaction provided strong evidence in support of the null hypothesis. For these stimuli and procedure, results suggest increased training does not necessarily maximize learning outcomes; both passive and trained experience likely supported adaptation. Findings may contribute to rehabilitation recommendations for listeners adapting to degraded speech signals.

Influence of face masks on recalibration of phonetic categories.

Previous research demonstrates listeners dynamically adjust phonetic categories in line with lexical context. While listeners show flexibility in adapting speech categories, recalibration may be constrained when variability can be attributed externally. It has been hypothesized that when listeners attribute atypical speech input to a causal factor, phonetic recalibration is attenuated. The current study investigated this theory directly by examining the influence of face masks, an external factor that affects both visual and articulatory cues, on the magnitude of phonetic recalibration. Across four experiments, listeners completed a lexical decision exposure phase in which they heard an ambiguous sound in either /s/-biasing or /ʃ/-biasing lexical contexts, while simultaneously viewing a speaker with a mask off, mask on the chin, or mask over the mouth. Following exposure, all listeners completed an auditory phonetic categorization test along an /ʃ/-/s/ continuum. In Experiment 1 (when no face mask was present during exposure trials), Experiment 2 (when the face mask was on the chin), Experiment 3 (when the face mask was on the mouth during ambiguous items), and Experiment 4 (when the face mask was on the mouth during the entire exposure phase), listeners showed a robust and equivalent phonetic recalibration effect. Recalibration manifested as greater proportion /s/ responses for listeners in the /s/-biased exposure group, relative to listeners in the /ʃ/-biased exposure group. Results support the notion that listeners do not causally attribute face masks with speech idiosyncrasies, which may reflect a general speech learning adjustment during the COVID-19 pandemic.

Sleep-Based Memory Consolidation Stabilizes Perceptual Learning of Noise-Vocoded Speech.

PURPOSE: Sleep-based memory consolidation has been shown to facilitate perceptual learning of atypical speech input including nonnative speech sounds, accented speech, and synthetic speech. The current research examined the role of sleep-based memory consolidation on perceptual learning for noise-vocoded speech, including maintenance of learning over a 1-week time interval. Because comprehending noise-vocoded speech requires extensive restructuring of the mapping between the acoustic signal and prelexical representations, sleep consolidation may be critical for this type of adaptation. Thus, the purpose of this study was to investigate the role of sleep-based memory consolidation on adaptation to noise-vocoded speech in listeners without hearing loss as a foundational step toward identifying parameters that can be useful to consider for auditory training with clinical populations. METHOD: Two groups of normal-hearing listeners completed a transcription training task with feedback for noise-vocoded sentences in either the morning or the evening. Learning was assessed through transcription accuracy before training, immediately after training, 12 hr after training, and 1 week after training for both trained and novel sentences. RESULTS: Both the morning and evening groups showed improved comprehension of noise-vocoded sentences immediately following training. Twelve hours later, the evening group showed stable gains (following a period of sleep), whereas the morning group demonstrated a decline in gains (following a period of wakefulness). One week after training, the morning and evening groups showed equivalent performance for both trained and novel sentences. CONCLUSION: Sleep-consolidated learning helps stabilize training gains for degraded speech input, which may hold clinical utility for optimizing rehabilitation recommendations.

Many tasks, same outcome: Role of training task on learning and maintenance of noise-vocoded speech.

Listeners who use cochlear implants show variability in speech recognition. Research suggests that structured auditory training can improve speech recognition outcomes in cochlear implant users, and a central goal in the rehabilitation literature is to identify factors that maximize training. Here, we examined factors that may influence perceptual learning for noise-vocoded speech in normal hearing listeners as a foundational step towards clinical recommendations. Three groups of listeners were exposed to anomalous noise-vocoded sentences and completed one of three training tasks: transcription with feedback, transcription without feedback, or talker identification. Listeners completed a word transcription test at three time points: immediately before training, immediately after training, and one week following training. Accuracy at test was indexed by keyword accuracy at the sentence-initial and sentence-final position for high and low predictability noise-vocoded sentences. Following training, listeners showed improved transcription for both sentence-initial and sentence-final items, and for both low and high predictability sentences. The training groups showed robust and equivalent learning of noise-vocoded sentences immediately after training. Critically, gains were largely maintained equivalently among training groups one week later. These results converge with evidence pointing towards the utility of non-traditional training tasks to maximize perceptual learning of noise-vocoded speech.

Lexically guided perceptual learning is robust to task-based changes in listening strategy.

Listeners use lexical information to resolve ambiguity in the speech signal, resulting in the restructuring of speech sound categories. Recent findings suggest that lexically guided perceptual learning is attenuated when listeners use a perception-focused listening strategy (that directs attention towards surface variation) compared to when listeners use a comprehension-focused listening strategy (that directs attention towards higher-level linguistic information). However, previous investigations used the word position of the ambiguity to manipulate listening strategy, raising the possibility that attenuated learning reflected decreased strength of lexical recruitment instead of a perception-oriented listening strategy. The current work tests this hypothesis. Listeners completed an exposure phase followed by a test phase. During exposure, listeners heard an ambiguous fricative embedded in word-medial lexical contexts that supported realization of the ambiguity as /∫/. At test, listeners categorized members of an /ɑsi/-/ɑ∫i/ continuum. Listening strategy was manipulated via exposure task (experiment 1) and explicit acknowledgement of the ambiguity (experiment 2). Compared to control participants, listeners who were exposed to the ambiguity showed more /∫/ responses at the test; critically, the magnitude of learning did not differ across listening strategy conditions. These results suggest that given sufficient lexical context, lexically guided perceptual learning is robust to task-based changes in listening strategy.

Lexically guided perceptual tuning of internal phonetic category structure.

Listeners use lexical information to retune the mapping between the acoustic signal and speech sound representations, resulting in changes to phonetic category boundaries. Other research shows that phonetic categories have a rich internal structure; within-category variation is represented in a graded fashion. The current work examined whether lexically informed perceptual learning promotes a comprehensive reorganization of internal category structure. The results showed a reorganization of internal structure for one but not both of the examined categories, which may reflect an attenuation of learning for distributions with extensive category overlap. This finding points towards potential input-driven constraints on lexically guided phonetic retuning.