Lexically-guided Perceptual Learning Research Articles

Auditory perceptual learning in autistic adults.

The automatic retuning of phoneme categories to better adapt to the speech of a novel talker has been extensively documented across various (neurotypical) populations, including both adults and children. However, no studies have examined auditory perceptual learning effects in populations atypical in perceptual, social, and language processing for communication, such as populations with autism. Employing a classic lexically-guided perceptual learning paradigm, the present study investigated perceptual learning effects in Australian English autistic and non-autistic adults. The findings revealed that automatic attunement to existing phoneme categories was not activated in the autistic group in the same manner as for non-autistic control subjects. Specifically, autistic adults were able to both successfully discern lexical items and to categorize speech sounds; however, they did not show effects of perceptual retuning to talkers. These findings may have implications for the application of current sensory theories (e.g., Bayesian decision theory) to speech and language processing by autistic individuals. LAY SUMMARY: Lexically guided perceptual learning assists in the disambiguation of speech from a novel talker. The present study established that while Australian English autistic adult listeners were able to successfully discern lexical items and categorize speech sounds in their native language, perceptual flexibility in updating speaker-specific phonemic knowledge when exposed to a novel talker was not available. Implications for speech and language processing by autistic individuals as well as current sensory theories are discussed.

Boosting lexical support does not enhance lexically guided perceptual learning.

A challenge for listeners is to learn the appropriate mapping between acoustics and phonetic categories for an individual talker. Lexically guided perceptual learning (LGPL) studies have shown that listeners can leverage lexical knowledge to guide this process. For instance, listeners learn to interpret ambiguous /s/-/∫/ blends as /s/ if they have previously encountered them in /s/-biased contexts like epi?ode. Here, we examined whether the degree of preceding lexical support might modulate the extent of perceptual learning. In Experiment 1, we first demonstrated that perceptual learning could be obtained in a modified LGPL paradigm where listeners were first biased to interpret ambiguous tokens as one phoneme (e.g., /s/) and then later as another (e.g., /∫/). In subsequent experiments, we tested whether the extent of learning differed depending on whether targets encountered predictive contexts or neutral contexts prior to the auditory target (e.g., epi?ode). Experiment 2 used auditory sentence contexts (e.g., "I love The Walking Dead and eagerly await every new . . ."), whereas Experiment 3 used written sentence contexts. In Experiment 4, participants did not receive sentence contexts but rather saw the written form of the target word (episode) or filler text (＃＃＃＃＃＃＃＃) prior to hearing the critical auditory token. While we consistently observed effects of context on in-the-moment processing of critical words, the size of the learning effect was not modulated by the type of context. We hypothesize that boosting lexical support through preceding context may not strongly influence perceptual learning when ambiguous speech sounds can be identified solely from lexical information. (PsycInfo Database Record (c) 2021 APA, all rights reserved).

Lexically-guided perceptual learning does generalize to new phonetic contexts

Lexically-guided and visually-guided perceptual learning have been argued to tap into the same general perceptual mechanism. Using the visually-guided paradigm, some have argued that the resulting retuning effect is specific to the phonetic context in which it is learned; which in turn has been used to argue that such retuning targets context-dependent sub-lexical units. We use three new experiments to study the generalizable nature of lexically-guided perceptual learning of fricative consonants and how type variation in the training stimuli affects it. In contrast to visually-guided retuning, we show that lexical retuning does generalize to new phonetic contexts, particularly when listeners are trained with type variation. This suggests that there is an abstract context-independent representation that is used in speech perception and during lexical retuning. While the same generalization is not clearly observed when type variation is eliminated, the lack of a clear interaction effect between training types prevents us from inferring that lexically-guided perceptual learning needs type variation within the training stimuli to generalize to new phonetic contexts. Furthermore, we point out that some of these effects are subtle and are only observable if we take into account pre-training group difference between the control and test groups.

The effect of intermittent noise on lexically-guided perceptual learning in native and non-native listening

There is ample evidence that both native and non-native listeners deal with speech variation by quickly tuning into a speaker and adjusting their phonetic categories according to the speaker’s ambiguous pronunciation. This process is called lexically-guided perceptual learning. Moreover, the presence of noise in the speech signal has previously been shown to change the word competition process by increasing the number of candidate words competing for recognition and slowing down the recognition process. Given that reliable lexical information should be available quickly to induce lexically-guided perceptual learning and that word recognition is slowed down in the presence of noise, and especially so for non-native listeners, the present study investigated whether noise interferes with lexically-guided perceptual learning in native and non-native listening. Native English and Dutch listeners were exposed to a story in English in clean speech or with stretches of noise. All the /l/ and /ɹ/ sounds in the story were replaced with an ambiguous sound half-way between /l/ and /ɹ/. Although noise altered the pattern of responses for the non-native listeners in a subsequent phonetic categorization task, both native and non-native listeners demonstrated lexically-guided perceptual learning in both clean and noisy listening conditions. We argue that the robustness of perceptual learning in the presence of intermittent noise for both native and non-native listeners is additional evidence for the remarkable flexibility of native and non-native perceptual systems even in adverse listening conditions.

A second chance for a first impression: Lexically guided perceptual learning reflects cumulative experience with a talker's phonetic input

Listeners use lexical knowledge to modify the mapping from acoustics to speech sounds, but the timecourse of experience that informs lexically guided perceptual learning (LGPL) is unknown. Some data suggest that learning depends on initial exposure to atypical productions, while other data suggest that learning reflects only the most recent exposure. Here we seek to reconcile these findings by assessing the type and timecourse of exposure that promote robust LGPL. In experiment 1, listeners were exposed to ambiguous fricatives embedded in either /s/- or /∫/-biasing contexts and then categorized items from an ashi-asi continuum at test. Learning was observed; the /s/-bias group showed more asi responses compared to the /∫/-bias group. In experiment 2, listeners heard both clear and ambiguous productions. Order and lexical bias were manipulated between-subjects, and perceptual learning occurred regardless of the order in which the productions were heard. In experiment 3, listeners heard both /s/- and /∫/-biased productions. Order differed between two exposure groups, and no difference between groups was observed at test. Moreover, the results showed a monotonic decrease in learning across experiments, in line with decreasing exposure to stable lexically biasing contexts, and were replicated across novel stimulus sets. The current results did not replicate previous findings showing that either initial or most recent experience are critical for LGPL. Rather, LGPL appears to reflect an aggregation of a talker's input over time.

Lexically-guided perceptual learning in early Cantonese-English bilinguals.

Bilinguals are capable of retuning phonetic categories in both languages through lexically-guided perceptual learning, but recent work suggests that some bilingual speakers may lose the ability to adapt in the native language. In the study reported here, early Cantonese-English bilinguals, who are on average English-dominant, successfully retuned Cantonese /f/. Scores of Cantonese-English dominance were not shown to correlate with phonetic retuning. The results are discussed in light of what may support the maintenance of perceptual flexibility in a lesser-used language.

No L1 privilege in talker adaptation

AbstractAs a rule, listening is easier in first (L1) than second languages (L2); difficult L2 listening can challenge even highly proficient users. We here examine one particular listening function, adaptation to novel talkers, in such a high-proficiency population: Dutch emigrants to Australia, predominantly using English outside the family, but all also retaining L1 proficiency. Using lexically-guided perceptual learning (Norris, McQueen & Cutler, 2003), we investigated these listeners’ adaptation to an ambiguous speech sound, in parallel experiments in both their L1 and their L2. A control study established that perceptual learning outcomes were unaffected by the procedural measures required for this double comparison. The emigrants showed equivalent proficiency in tests in both languages, robust perceptual adaptation in their L2, English, but no adaptation in L1. We propose that adaptation to novel talkers is a language-specific skill requiring regular novel practice; a limited set of known (family) interlocutors cannot meet this requirement.

Effects of processing depth on lexically guided perceptual learning

Listeners use lexical information to modify the mapping to representations for individual speech sounds. This mechanism, termed lexically guided perceptual learning (LGPL), results in long-lasting changes to speech sound categories and may be modulated by attention mechanisms. The literature on LGPL has demonstrated that learning may be influenced by explicit or implicit attention towards anomalous aspects of the input and may be affected by individual factors, such as cognitive abilities. The current study used three experiments to examine the degree to which graded lexical recruitment, indexed by explicit attention to the lexicon compared to other stimulus features, influenced the magnitude of LGPL. Listeners completed an exposure phase, where they heard an ambiguous phoneme, midway between /s/ and /ʃ/. Attention was manipulated across experiments through task instructions during exposure such that attention was shifted either towards lexical information (lexical decision task), surface variation (amplitude judgment task), or syntactic knowledge (syntactic decision task). Following exposure, all participants completed a phoneme identification task for members of an /s/-/ʃ/ continuum. Preliminary results indicate that LGPL occurred in each experiment; however, the magnitude of learning differed as a function of attention. The final results will be discussed in terms of constraints of the LGPL mechanism.

Task differences do not impede overall learning when adapting to a novel sound

Lexically guided perceptual learning (LGPL) and second-language learning (L2) research seeks to understand how listeners adapt to novel speech sounds. In LGPL, listeners shift their perception of a native phonetic contrast in response to hearing an ambiguous token embedded in an unambiguous lexical context. In L2 tasks, often involve categorizing non-native sounds, usually with explicit feedback. In general, L2 learning is seen as more effortful and individually variable than LGPL. However, paradigms differ in terms of stimuli (native vs. non-native phonetic contrasts) as well as tasks (lexically-guided implicit feedback vs. explicit feedback). To test whether L2-type vs. LGPL-type tasks yield differences in learning, participants were trained using an L2-style task to shift their native boundary along an /s/ to /sh/ continuum. With feedback, participants categorized the midpoint token as one novel object, and an endpoint token (counterbalanced across subjects) as another novel object. After training, a boundary shift comparable to previous studies using the LGPL task was found, suggesting that explicit and lexically-guided feedback produce similar magnitude of learning. Despite this, participants in the L2-style task experienced lower accuracy and more variability in perception of the continuum endpoints, suggesting that task differences partially explain less consistency across individuals in L2 research.

Stimulus-directed attention attenuates lexically-guided perceptual learning.

Studies on perceptual learning are motivated by phonetic variation that listeners encounter across speakers, items, and context. In this study, the authors investigate what control the listener has over the perceptual learning of ambiguous /s/ pronunciations through inducing changes in their attentional set. Listeners' attention is manipulated during a lexical decision exposure task such that their attention is directed at the word-level for comprehension-oriented listening or toward the signal for perception-oriented listening. In a categorization task with novel words, listeners in the condition that maximally biased listeners toward comprehension-oriented attentional sets showed the most perceptual learning. Focus on higher levels of linguistic meaning facilitated generalization to new words. These results suggest that the way in which listeners attend to the speech stream affects how linguistic categories are updated, providing insight into the qualitative differences in perceptual learning between the psychophysics and language-focused literatures.

Lexically-guided perceptual learning in non-native listening

There is ample evidence that native and non-native listeners use lexical knowledge to retune their native phonetic categories following ambiguous pronunciations. The present study investigates whether a non-native ambiguous sound can retune non-native phonetic categories. After a brief exposure to an ambiguous British English [l/ɹ] sound, Dutch listeners demonstrated retuning. This retuning was, however, asymmetrical: the non-native listeners seemed to show (more) retuning of the /ɹ/ category than of the /l/ category, suggesting that non-native listeners can retune non-native phonetic categories. This asymmetry is argued to be related to the large phonetic variability of /r/ in both Dutch and English.