A Special Role of Syllables, But Not Vowels or Consonants, for Nonadjacent Dependency Learning

Successful language processing entails tracking (morpho)syntactic relationships between distant units of speech, so-called nonadjacent dependencies (NADs). Many cues to such dependency relations have been identified, yet the linguistic elements encoding them have received little attention. In the present investigation, we tested whether and how these elements, here syllables, consonants, and vowels, affect behavioral learning success as well as learning-related changes in neural activity in relation to item-specific NAD learning. In a set of two EEG studies with adults, we compared learning under conditions where either all segment types (Experiment 1) or only one segment type (Experiment 2) was informative. The collected behavioral and ERP data indicate that, when all three segment types are available, participants mainly rely on the syllable for NAD learning. With only one segment type available for learning, adults also perform most successfully with syllable-based dependencies. Although we find no evidence for successful learning across vowels in Experiment 2, dependencies between consonants seem to be identified at least passively at the phonetic-feature level. Together, these results suggest that successful item-specific NAD learning may depend on the availability of syllabic information. Furthermore, they highlight consonants' distinctive power to support lexical processes. Although syllables show a clear facilitatory function for NAD learning, the underlying mechanisms of this advantage require further research.

Effects of Verb Network Strengthening Treatment on Sound-Level and Speech Production Errors in Individuals With Aphasia and Acquired Apraxia of Speech

Purpose This retrospective pilot study investigated whether sound-level and speech production errors decreased in confrontation naming following Verb Network Strengthening Treatment (VNeST) for four participants with acquired apraxia of speech (A-AOS) and aphasia for whom lexical retrieval was previously reported. Specifically, we investigated a potential increase in correct number of syllables per word and posttreatment changes across three domains of speech: segmental production, fluency, and prosody. It was hypothesized that treatment shown to increase lexical retrieval in persons with aphasia and A-AOS could potentially facilitate a reduction in sound-level and speech production errors consistent with dual diagnoses of A-AOS and aphasia. Method Naming responses from four participants with aphasia and A-AOS who previously participated in VNeST studies were investigated for correct number of syllables per word and measures of segmental speech, fluency, and prosody. Results Significant gains in at least one measure of speech production were reported for three of the participants. One participant demonstrated decreased segmental speech errors, two showed significant reduction on syllable segmentation, and two demonstrated a significant reduction on false starts and pauses. Significant gains in production of correct number of syllables were limited to one participant, and one participant did not demonstrate increased accuracy on any measure of speech production. Conclusions While speech production errors consistent with motor speech impairment cannot always be definitively distinguished from the confound of aphasia, two participants produced significantly decreased segmentation of syllables, a characteristic unique to A-AOS. The sound-level and speech production changes recorded may be attributed to a combination of interacting motor and language processes and resource allocation. In addition, specific components of VNeST may have contributed to speech production changes. Future work will focus on a prospective study of effects of language therapy (e.g., VNeST) on measures of speech production with investigation beyond the single-word level.

Speech rhythms and their neural foundations

The recognition of spoken language has typically been studied by focusing on either words or their constituent elements (for example, low-level features or phonemes). More recently, the 'temporal mesoscale' of speech has been explored, specifically regularities in the envelope of the acoustic signal that correlate with syllabic information and that play a central role in production and perception processes. The temporal structure of speech at this scale is remarkably stable across languages, with a preferred range of rhythmicity of 2- 8 Hz. Importantly, this rhythmicity is required by the processes underlying the construction of intelligible speech. A lot of current work focuses on audio-motor interactions in speech, highlighting behavioural and neural evidence that demonstrates how properties of perceptual and motor systems, and their relation, can underlie the mesoscale speech rhythms. The data invite the hypothesis that the speech motor cortex is best modelled as a neural oscillator, a conjecture that aligns well with current proposals highlighting the fundamental role of neural oscillations in perception and cognition. The findings also show motor theories (of speech) in a different light, placing new mechanistic constraints on accounts of the action-perception interface.