What memory representation is acquired during nonword speech production learning? The influence of stimulus features and training modality on nonword encoding

An instance-based model account of the benefits of varied practice in visuomotor skill

Exposing learners to variability during training has been demonstrated to improve performance in subsequent transfer testing. Such variability benefits are often accounted for by assuming that learners are developing some general task schema or structure. However much of this research has neglected to account for differences in similarity between varied and constant training conditions. In a between-groups manipulation, we trained participants on a simple projectile launching task, with either varied or constant conditions. We replicate previous findings showing a transfer advantage of varied over constant training. Furthermore, we show that a standard similarity model is insufficient to account for the benefits of variation, but, if the model is adjusted to assume that varied learners are tuned towards a broader generalization gradient, then a similarity-based model is sufficient to explain the observed benefits of variation. Our results therefore suggest that some variability benefits can be accommodated within instance-based models without positing the learning of some schemata or structure.

Dissimilar Phonemes Create a Contextual Interference Effect During a Nonword Repetition Task

Purpose: The contextual interference effect is a motor learning phenomenon where conditions that decrease overall learning during practice enhance overall learning with new tasks. In the limb literature, this effect is observed when different practice conditions are used (e.g., blocked vs. random practice schedules). In speech motor learning, contextual interference effects are mixed. The differences observed during speech motor learning may be due to the stimuli used. We hypothesized that dissimilar phonemes might create interference during speech motor learning, such that training accuracy would decrease. However, generalization accuracy would increase compared to practice with nonwords containing similar phonemes.

Method: Thirty young adults with typical speech and hearing participated in a motor learning study using a cross-over design. Participants engaged in nonword repetition training followed by an immediate retention and transfer task with two sets of nonwords: nonwords with similar phonemes and nonwords with dissimilar phonemes. Percent consonants correct were calculated to examine the effects of the two different types of nonwords based on the stage of skill acquisition.

Results: A contextual interference effect was observed in this study using nonwords that varied in phonemic similarity. Nonwords with similar phonemes were produced with greater accuracy during the training stage of skill acquisition, and nonwords with dissimilar phonemes were produced with greater accuracy during the transfer stage.

Conclusion: The proposed hypothesis for this study was met – practicing nonwords with dissimilar phonemes resulted in greater accuracy in the transfer phase of this experiment. Results indicate that phonemic dissimilarity produced contextual interference and influenced speech motor learning. These results indicate that the linguistic properties of stimuli must be factored into speech motor learning. Future research should explore if other linguistic variables interact with variables of motor learning to enhance speech practice and generalization outcomes.

Phoneme and Stress Programming Interact During Nonword Repetition Learning

Purpose Lexical stress and phoneme processes converge during phonological encoding, but the nature of the convergence has been debated. Stress patterns and phonemes may be integrated automatically and rigidly, resulting in a unified representation. Alternatively, stress and phoneme may be processed interactively based on sublexical contexts. The purpose of this study was to evaluate the extent to which the lexical stress and phoneme processing interact in a novel nonword learning paradigm. Method Twenty-seven adults with typical speech skills were trained to produce nonwords with specific phonemes, syllables, and stress patterns (Set 1) to an accuracy criterion. Then, participants repeated nonwords that varied from Set 1 in syllable position (Set 2), phoneme sequence (Set 3), included new phonemes (Set 4), or had new phonemes and stress patterns (Set 5). Nonword productions were perceptually analyzed, and phoneme and stress errors were counted. Results Participants' produced Set 1 nonwords with few phonemic or stress errors after training; a similar number of both types of errors were produced when comparing Sets 2 and 3. Greater phoneme and stress errors were produced on nonwords from Sets 4 and 5 compared to Sets 1-3. The highest number of phonemic errors occurred in Set 4 nonwords. There was no difference in the number of stress errors produced on nonwords in Sets 4 and 5. Conclusion The results of this study suggested that lexical stress and phoneme processing co-occurred and interacted during nonword productions. Trained stress patterns were learned during training; however, no evidence for a unified representation was observed. Negative interference was observed in nonwords with new phonemes and trained stress patterns, suggesting online phoneme processing may have dominated and interfered with the retrieval of stored metrical frames.