Role of cognitive control in resolving two types of conflict during spoken word production.

A theoretically- and clinically-important issue for understanding word retrieval is how speakers resolve conflict during linguistic tasks. This study investigated two types of conflict resolution: prepotent conflict, when one dominant incorrect response must be suppressed; and underdetermined conflict, when multiple reasonable responses compete. The congruency sequence effect paradigm was used to assess trial-to-trial changes in reaction time and accuracy during word production tasks with either prepotent or underdetermined conflict. Pictures were named faster on trials with low-conflict as compared to high-conflict regardless of conflict type. This effect was modulated by the amount of conflict experienced on the previous trial for both tasks. These results suggest that resolution of underdetermined and prepotent conflict may engage the same general cognitive mechanism. This work expands our understanding of the relationship between cognitive control and word production and can inform clinical approaches for people with anomia.

Factors Affecting Nonnative Consonant Cluster Learning.

PURPOSE: Nonnative consonant cluster learning has become a useful experimental approach for learning about speech motor learning, and we sought to enhance our understanding of this area and to establish best practices for this type of research. METHOD: One hundred twenty individuals completed a nonnative consonant cluster learning task within a speech motor learning paradigm. Following a brief prepractice, participants then practiced the production of eight word-initial nonnative consonant clusters embedded in bisyllabic nonwords (e.g., GD in /gdivu/). The clusters ranged in difficulty according to linguistic typology and sonority sequencing. Acquisition was operationalized as the change across the practice section and learning was assessed with two retention sessions (R1: 30 min after practice; R2: 2 days after practice). We evaluated changes in accuracy as well as in the acoustic details of the cluster production at each time point. RESULTS: Overall, participants improved in their production of the consonant clusters. Accuracy increased, and duration measures decreased in specific measures associated with cluster production. The change in coordination measured in the acoustics changed both for clusters that were incorrectly produced and for those that were correctly produced, indicating continued motor learning even in accurate tokens. CONCLUSIONS: These results aid our understanding of the complexity of nonnative consonant cluster learning. In particular, both factors related to both phonological and speech motor control properties affect the learning of novel speech sequences. SUPPLEMENTAL MATERIAL: https://doi.org/10.23641/asha.21844185.

Examining the Relationship Between Speech Perception, Production Distinctness, and Production Variability.

Several studies have demonstrated that individuals' ability to perceive a speech sound contrast is related to the production of that contrast in their native language. The theoretical account for this relationship is that speech perception and production have a shared multimodal representation in relevant sensory spaces (e.g., auditory and somatosensory domains). This gives rise to a prediction that individuals with more narrowly defined targets will produce greater separation between contrasting sounds, as well as lower variability in the production of each sound. However, empirical studies that tested this hypothesis, particularly with regard to variability, have reported mixed outcomes. The current study investigates the relationship between perceptual ability and production ability, focusing on the auditory domain. We examined whether individuals' categorical labeling consistency for the American English /ε/-/æ/ contrast, measured using a perceptual identification task, is related to distance between the centroids of vowel categories in acoustic space (i.e., vowel contrast distance) and to two measures of production variability: the overall distribution of repeated tokens for the vowels (i.e., area of the ellipse) and the proportional within-trial decrease in variability as defined as the magnitude of self-correction to the initial acoustic variation of each token (i.e., centering ratio). No significant associations were found between categorical labeling consistency and vowel contrast distance, between categorical labeling consistency and area of the ellipse, or between categorical labeling consistency and centering ratio. These null results suggest that the perception-production relation may not be as robust as suggested by a widely adopted theoretical framing in terms of the size of auditory target regions. However, the present results may also be attributable to choices in implementation (e.g., the use of model talkers instead of continua derived from the participants' own productions) that should be subject to further investigation.

Does Voicing Affect Patterns of Transfer in Nonnative Cluster Learning?

Purpose Previous studies have demonstrated that speakers can learn novel speech sequences, although the content and specificity of the learned speech motor representations remain incompletely understood. We investigated these representations by examining transfer of learning in the context of nonnative consonant clusters. Specifically, we investigated whether American English speakers who learn to produce either voiced or voiceless stop-stop clusters (e.g., /gd/ or /kt/) exhibit transfer to the other voicing pattern. Method Each participant (n = 34) was trained on disyllabic nonwords beginning with either voiced (/gd/, /db/, /gb/) or voiceless (/kt/, /kp/, /tp/) onset consonant clusters (e.g., /gdimu/, /ktaksnæm/) in a practice-based speech motor learning paradigm. All participants were tested on both voiced and voiceless clusters at baseline (prior to practice) and in two retention sessions (20 min and 2 days after practice). We compared changes in cluster accuracy and burst-to-burst duration between baseline and each retention session to evaluate learning (performance on the trained clusters) and transfer (performance on the untrained clusters). Results Participants in both training conditions improved with respect to cluster accuracy and burst-to-burst duration for the clusters they practiced on. A bidirectional transfer pattern was found, such that participants also improved the cluster accuracy and burst-to-burst duration for the clusters with the other untrained voicing pattern. Post hoc analyses also revealed that improvement in the production of untrained stop-fricative clusters that originally were added as filler items. Conclusion Our findings suggest the learned speech motor representations may encode the information about the coordination of oral articulators for stop-stop clusters independently from information about the coordination of oral and laryngeal articulators.

Behavioral and neurological effects of tDCS on speech motor recovery: A single-subject intervention study.

This paper reports a feasibility study designed to evaluate the behavioral and neurological effects of using transcranial direct current stimulation (tDCS) in conjunction with speech motor learning treatment for individuals with acquired speech impairment subsequent to stroke. Most of the research using tDCS to enhance treatment outcomes in stroke recovery has focused on either limb motor control or aphasia treatment. Using a multiple-baseline multiple-probe crossover design, we compared both behavioral and brain connectivity-based outcomes following speech motor learning treatment with both Active tDCS and Sham tDCS. We observed that both treatment phases led to improvement in short-term maintenance, but that Active tDCS was associated with greater long-term maintenance improvement. Active tDCS was also associated with an increase in functional connectivity in the left hemisphere and interhemispherically in an ROI-based network analysis examining correlations among areas associated with speech production and acquired speech impairment. This report supports the possibility that tDCS may enhance both behavioral and neurological outcomes and indicates the importance of additional work in this area, although replication is required to confirm the extent and consistency of tDCS benefits on speech motor learning treatment outcomes.

The impact of morphophonological patterns on verb production: evidence from acquired morphological impairment.

Although much of the research on morphology and aphasia has focused specifically on the distinction between regular and irregular verb production, individuals with aphasia often present with differences in performance within these categories. While these within-category differences are relatively understudied, they have the potential to inform our understanding of the morphological processing system and treatment protocols for morphological impairment. The present study examines how morphophonological patterns in English impact past-tense production within the categories of regular and irregular verbs based on errors of an individual with acquired morphological impairment. Acquired morphological impairment was demonstrated by performance on two reading tasks. First, the individual produced more final consonant deletion errors in morphologically complex words (prays→[pre]) compared to homophones (praise→[pre]). Second, morphological deletion errors were found to occur at comparable rates for inflected regular verbs (sinned→sin) and inflected irregular verbs (won→win), whereas the analogous error (e.g. ton→tin) never occurred on the monomorphemic pairs. In order to examine differences within each category, we used a past-tense elicitation task designed to analyse the effect of differences in morphophonological pattern frequency on accuracy and error patterns in production. We found production of both regular and irregular verbs was affected by the extent to which different morphophonological patterns are supported in the language (i.e. the number of phonologically similar words within the lexicon which take the same inflectional change). These results provide evidence that morphophonological patterns are encoded in a way that impact morphological production, a finding which has both clinical and theoretical implications.

Using tDCS to facilitate motor learning in speech production: The role of timing.

There exists debate regarding the extent to which transcranial direct current stimulation (tDCS) can affect or enhance human behavior. Here, we examined a previously unexplored domain: speech motor learning. We investigated whether speech motor learning in unimpaired participants can be enhanced using a single-session tDCS experiment, and investigated whether the timing of tDCS relative to a behavioral task affected performance. Participants (N = 80) performed a twenty minute learning task with nonwords containing non-native consonant clusters (e.g., GDEEVOO), and were assigned to groups receiving either sham or active tDCS either immediately before or during the task. Both accuracy and properties of errors were examined throughout the course of the practice task, and then practice was compared to a retention period 30 min later (R1) and two days later (R2). For cluster and whole-(non)word accuracy measures, acquisition was observed for all groups during the practice session. Compared to the beginning of practice, the tDCS-Before group showed significantly greater improvement than both the sham group and the tDCS-During group at R1. An effect was also observed for vowel duration in errors (/gdivu/ â†’ [gədivu]), with the tDCS-Before group showing significant shortening of vowel errors throughout practice. Overall, the findings suggest that tDCS can improve speech motor learning, and that the improvement may be greater when tDCS is applied immediately before practice, warranting further exploration of this new domain for tDCS research.

Robotic Arm Rehabilitation in Chronic Stroke Patients With Aphasia May Promote Speech and Language Recovery (but Effect Is Not Enhanced by Supplementary tDCS).

Objective: This study aimed to determine the extent to which robotic arm rehabilitation for chronic stroke may promote recovery of speech and language function in individuals with aphasia. Methods: We prospectively enrolled 17 individuals from a hemiparesis rehabilitation study pairing intensive robot assisted therapy with sham or active tDCS and evaluated their speech (N = 17) and language (N = 9) performance before and after a 12-week (36 session) treatment regimen. Performance changes were evaluated with paired t-tests comparing pre- and post-test measures. There was no speech therapy included in the treatment protocol. Results: Overall, the individuals significantly improved on measures of motor speech production from pre-test to post-test. Of the subset who performed language testing (N = 9), overall aphasia severity on a standardized aphasia battery improved from pre-test baseline to post-test. Active tDCS was not associated with greater gains than sham tDCS. Conclusions: This work indicates the importance of considering approaches to stroke rehabilitation across different domains of impairment, and warrants additional exploration of the possibility that robotic arm motor treatment may enhance rehabilitation for speech and language outcomes. Further investigation into the role of tDCS in the relationship of limb and speech/language rehabilitation is required, as active tDCS did not increase improvements over sham tDCS.

Assessing automatic VOT annotation using unimpaired and impaired speech.

Investigating speech processes often involves analysing data gathered by phonetically annotating speech recordings. Yet, the manual annotation of speech can often be resource intensive-requiring substantial time and labour to complete. Recent advances in automatic annotation methods offer a way to reduce these annotation costs by replacing manual annotation. For researchers and clinicians, the viability of automatic methods depends whether one can draw similar conclusions about speech processes from automatically annotated speech as one would from manually annotated speech. Here, we evaluate how well one automatic annotation tool, AutoVOT, can approximate manual annotation. We do so by comparing analyses of automatically and manually annotated speech in two studies. We find that, with some caveats, we are able to draw the same conclusions about speech processes under both annotation methods. The findings suggest that automatic methods may be a viable way to reduce phonetic annotation costs in the right circumstances. We end with some guidelines on if and how well AutoVOT may be able to replace manual annotation in other data sets.

The Impact of Feedback Frequency on Performance in a Novel Speech Motor Learning Task.

Purpose: This study investigated whether whole nonword accuracy, phoneme accuracy, and acoustic duration measures were influenced by the amount of feedback speakers without impairment received during a novel speech motor learning task. Method: Thirty-two native English speakers completed a nonword production task across 3 time points: practice, short-term retention, and long-term retention. During practice, participants received knowledge of results feedback according to a randomly assigned schedule (100%, 50%, 20%, or 0%). Changes in nonword accuracy, phoneme accuracy, nonword duration, and initial-cluster duration were compared among feedback groups, sessions, and stimulus properties. Results: All participants improved phoneme and whole nonword accuracy at short-term and long-term retention time points. Participants also refined productions of nonwords, as indicated by a decrease in nonword duration across sessions. The 50% group exhibited the largest reduction in duration between practice and long-term retention for nonwords with native and nonnative clusters. Conclusions: All speakers, regardless of feedback schedule, learned new speech motor behaviors quickly with a high degree of accuracy and refined their speech motor skills for perceptually accurate productions. Acoustic measurements may capture more subtle, subperceptual changes that may occur during speech motor learning. Supplemental Materials: https://doi.org/10.23641/asha.5116324.

Identification and Remediation of Phonological and Motor Errors in Acquired Sound Production Impairment.

Purpose: This study aimed to test whether an approach to distinguishing errors arising in phonological processing from those arising in motor planning also predicts the extent to which repetition-based training can lead to improved production of difficult sound sequences. Method: Four individuals with acquired speech production impairment who produced consonant cluster errors involving deletion were examined using a repetition task. We compared the acoustic details of productions with deletion errors in target consonant clusters to singleton consonants. Changes in accuracy over the course of the study were also compared. Results: Two individuals produced deletion errors consistent with a phonological locus of the errors, and 2 individuals produced errors consistent with a motoric locus of the errors. The 2 individuals who made phonologically driven errors showed no change in performance on a repetition training task, whereas the 2 individuals with motoric errors improved in their production of both trained and untrained items. Conclusions: The results extend previous findings about a metric for identifying the source of sound production errors in individuals with both apraxia of speech and aphasia. In particular, this work may provide a tool for identifying predominant error types in individuals with complex deficits.

Covert contrast in velar fronting: An acoustic and ultrasound study.

There is growing evidence that speech sound acquisition is a gradual process, with instrumental measures frequently revealing covert contrast in errors perceived to involve phonemic substitution. Ultrasound imaging has the potential to expand our understanding of covert contrast by showing whether a child uses different tongue shapes while producing sounds that are perceived as neutralised. This study used an ultrasound measure (Dorsum Excursion Index) and acoustic measures (VOT and spectral moments of the burst) to investigate overt and covert contrast between velar and alveolar stops in child speech. Participants were two children who produced a perceptually overt velar-alveolar contrast and two children who neutralised the contrast via velar fronting. Both acoustic and ultrasound measures revealed significant differences between perceptually distinct velar and alveolar targets. One child with velar fronting demonstrated covert contrast in one acoustic and one ultrasound measure; the other showed no evidence of contrast. Clinical implications are discussed in this article.

Cascading activation from lexical processing to letter-level processing in written word production.

Descriptions of language production have identified processes involved in producing language and the presence and type of interaction among those processes. In the case of spoken language production, consensus has emerged that there is interaction among lexical selection processes and phoneme-level processing. This issue has received less attention in written language production. In this paper, we present a novel analysis of the writing-to-dictation performance of an individual with acquired dysgraphia revealing cascading activation from lexical processing to letter-level processing. The individual produced frequent lexical-semantic errors (e.g., chipmunk → SQUIRREL) as well as letter errors (e.g., inhibit → INBHITI) and had a profile consistent with impairment affecting both lexical processing and letter-level processing. The presence of cascading activation is suggested by lower letter accuracy on words that are more weakly activated during lexical selection than on those that are more strongly activated. We operationalize weakly activated lexemes as those lexemes that are produced as lexical-semantic errors (e.g., lethal in deadly → LETAHL) compared to strongly activated lexemes where the intended target word (e.g., lethal) is the lexeme selected for production.

Misperceptions of spoken words: data from a random sample of American English words.

This study reports a detailed analysis of incorrect responses from an open-set spoken word recognition experiment of 1428 words designed to be a random sample of the entire American English lexicon. The stimuli were presented in six-talker babble to 192 young, normal-hearing listeners at three signal-to-noise ratios (0, +5, and +10 dB). The results revealed several patterns: (1) errors tended to have a higher frequency of occurrence than did the corresponding target word, and frequency of occurrence of error responses was significantly correlated with target frequency of occurrence; (2) incorrect responses were close to the target words in terms of number of phonemes and syllables but had a mean edit distance of 3; (3) for syllables, substitutions were much more frequent than either deletions or additions; for phonemes, deletions were slightly more frequent than substitutions; both were more frequent than additions; and (4) for errors involving just a single segment, substitutions were more frequent than either deletions or additions. The raw data are being made available to other researchers as supplementary material to form the beginnings of a database of speech errors collected under controlled laboratory conditions.

On the nature of sonority in spoken word production: evidence from neuropsychology.

The concept of sonority - that speech sounds can be placed along a universal sonority scale that affects syllable structure - has proved valuable in accounting for a wide spectrum of linguistic phenomena and psycholinguistic findings. Yet, despite the success of this concept in specifying principles governing sound structure, several questions remain about sonority. One issue that needs clarification concerns its locus in the processes involved in spoken language production, and specifically whether sonority affects the computation of abstract word form representations (phonology), the encoding of context-specific features (phonetics), or both of these processes. This issue was examined in the present study investigating two brain-damaged individuals with impairment arising primarily from deficits affecting phonological and phonetic processes, respectively. Clear effects of sonority on production accuracy were observed in both individuals testing word onsets and codas in word production. These findings indicate that the underlying principles governing sound structure that are captured by the notion of sonority play a role at both phonological and phonetic levels of processing. Furthermore, aspects of the errors recorded from our participants revealed features of syllabic structure proposed under current phonological theories (e.g., articulatory phonology).

Phonological and motor errors in individuals with acquired sound production impairment.

PURPOSE: This study aimed to compare sound production errors arising due to phonological processing impairment with errors arising due to motor speech impairment. METHOD: Two speakers with similar clinical profiles who produced similar consonant cluster simplification errors were examined using a repetition task. We compared both overall accuracy and acoustic details of hundreds of productions with target consonant clusters to tokens with singletons. Changes in accuracy over the course of the study were also compared. RESULTS: In target words with consonant cluster simplification, the individual whose errors reflected phonological impairment produced articulatory timing consistent with singleton onsets. These productions improved when resyllabification was possible, but error rates were not affected by exposure. In contrast, the individual with motoric-based errors produced simplifications that contained the articulatory timing associated with clusters. Accuracy was not affected by the ability to resyllabify, but it did significantly improve following repeated production. CONCLUSIONS: Our findings reveal clear differences between errors arising in phonological processing and in motor planning that reflect the underlying systems. The changes over the course of the study suggest that error types with different sources are responsive to different intervention strategies.

Finding levels of abstraction in speech production: evidence from sound-production impairment.

A widely held view in linguistics and psycholinguistics is that there are distinct levels of processing for context-independent and context-specific representations of sound structure. Recently, this view has been disputed, in part because of the absence of clear evidence that there are abstract mental representations of discrete sound-structure units. Here, we present novel evidence that separate context-independent and context-specific representations of sound structure are supported by distinct brain mechanisms that can be selectively impaired in individuals with acquired brain deficits. Acoustic data from /s/-deletion errors of 2 aphasic speakers suggest both a phonological level of processing at which sound representations (e.g., /p/) do not specify context-specific detail (e.g., aspirated or unaspirated) and a distinct level at which context-specific information is represented. These data help constrain accounts of sound-structure processing in word production and crucially support the claim that context-independent linguistic information affects language production.

Perceptual adaptation and intelligibility of multiple talkers for two types of degraded speech.

Talker intelligibility and perceptual adaptation under cochlear implant (CI)-simulation and speech in multi-talker babble were compared. The stimuli consisted of 100 sentences produced by 20 native English talkers. The sentences were processed to simulate listening with an eight-channel CI or were mixed with multi-talker babble. Stimuli were presented to 400 listeners in a sentence transcription task (200 listeners in each condition). Perceptual adaptation was measured for each talker by comparing intelligibility in the first 20 sentences of the experiment to intelligibility in the last 20 sentences. Perceptual adaptation patterns were also compared across the two degradation conditions by comparing performance in blocks of ten sentences. The most intelligible talkers under CI-simulation also tended to be the most intelligible talkers in multi-talker babble. Furthermore, listeners demonstrated a greater degree of perceptual adaptation in the CI-simulation condition compared to the multi-talker babble condition although the extent of adaptation varied widely across talkers. Listeners reached asymptote later in the experiment in the CI-simulation condition compared with the multi-talker babble condition. Overall, these two forms of degradation did not differ in their effect on talker intelligibility, although they did result in differences in the amount and time-course of perceptual adaptation.

Adaptation to frozen babble in spoken word recognition.

Previous research has shown that listeners can adapt to particular samples of noise, a phenomenon known as "frozen noise" [Langhans and Kohlrausch, J. Acoust. Soc. Am. 91, 3456-3470 (1992)]. However, no studies have reported a similar effect for multi-talker babble. The results of this study comparing open-set word recognition in multi-talker babble showed that listeners are significantly more accurate when the babble is fixed than when the babble is random. This documents the effect the authors refer to as "frozen babble."