Dissociation between phonological working memory structures and motor programming units during speech motor-sequence learning

Purpose: This study investigated the nature of phonological working memory (PWM) structures and speech motor programming units by examining how performance gains from practicing non-native phoneme sequences generalize to novel sequences that overlap to varying degrees with the practiced sequences.Method: CCVCC words were constructed using consonant clusters that violated English phonological constraints, thus making them difficult to produce initially. After practicing a subset of the words over two consecutive days, participants were tested on the production of several types of word pairs, including novel words containing unpracticed clusters, practiced cluster words containing consonant clusters that were practiced but in different words from the test words, and fully learned words that were practiced in their entirety.Results: Utterance duration improvements from practicing clusters in one syllabic context fully transferred to novel words that included these clusters, while error rate improvements from practicing clusters in one syllabic context only partially generalized to new syllables utilizing these practiced clusters. Additionally, error rates for the first word in the pair (which depend primarily on motor program structure) showed partial improvements for learned clusters regardless of whether the cluster was practiced in the same part of the syllabic frame (onset or coda), whereas error rates for the second word (which reflect both PWM and motor programming mechanisms) were higher than even novel words if the cluster was practiced in the wrong syllable frame location, presumably due to interference effects in PWM. Conclusions: These results provide support for an onset-nucleus-coda syllabic frame structure in PWM and a syllable-frame-independent representation of common phoneme sub-sequences for motor programs.