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

Psycholinguistic effects, types of impairments and processing levels in word production: Can we reduce confusions?

This commentary highlights three common difficulties faced by the literature that aims to specify models of speech production based on the performance of aphasic speakers, taking as a springboard a recent study by Mailend et al. These include: (1) difficulties with theoretical assumptions which linki psycholinguistic effects unequivocally to one processing level; (2) difficulties using clinical classifications to localize experimental effects; (3) difficulties making theoretical inferences given the controversial nature of the representations that characterize different processing levels. We argue that these three types of difficulties could be ameliorated by studies in which: (1) the level of psycholinguistic effects is demonstrated with converging analyses; (2) clinical classification is not taken as a starting point in studies investigating the nature of an impairment, but, instead, associations between clusters of symptoms are carefully analysed; (3) The nature of processing levels associated with deficits is made clear and results are not over-interpreted as supporting models whose characteristics go beyond an explanation of the results.

Disentangling the Psycholinguistic Loci of Anomia with Cognitive Psychometric Models

This article reviews advanced statistical techniques for measuring impairments in object naming, particularly in the context of stroke-induced aphasia. Traditional testing strategies can be challenged by the multifaceted nature of impairments that arise due to the complex relationships between localized brain damage and disruption to the cognitive processes required for successful object naming. Cognitive psychometric models can combine response-type analysis with item-response theory to yield accurate estimates of multiple abilities using data collected from a single task. The models also provide insights about how the test items can be challenging in different ways. Although more work is needed to fully optimize their clinical utility in practice, these formal concepts can guide thoughtful selection of stimuli used in treatment or assessment, as well as providing a framework to interpret response-type data.

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.

Apraxia of speech and the study of speech production impairments: Can we avoid further confusion? Reply to Romani (2021)

We agree with Cristina Romani (CR) about reducing confusion and agree that the issues raised in her commentary are central to the study of apraxia of speech (AOS). However, CR critiques our approach from the perspective of basic cognitive neuropsychology. This is confusing and misleading because, contrary to CR's claim, we did not attempt to inform models of typical speech production. Instead, we relied on such models to study the impairment in the clinical category of AOS (translational cognitive neuropsychology). Thus, the approach along with the underlying assumptions is different. This response aims to clarify these assumptions, broaden the discussion regarding the methodological approach, and address CR's concerns. We argue that our approach is well-suited to meet the goals of our recent studies and is commensurate with the current state of the science of AOS. Ultimately, a plurality of approaches is needed to understand a phenomenon as complex as AOS.

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.

To Lump or to Split? Possible Subtypes of Apraxia of Speech

BACKGROUND

The speculation that apraxia of speech (AOS) is not a unitary diagnosis, but consists of different subtypes instead, has been around for decades. However, attempts to empirically substantiate such a notion remain few and far between.

AIMS

The primary objective of this article is to consider the different bases for identifying subtypes of AOS, review existing evidence regarding subtypes under each classification basis, and provide discussion and implications for future research.

MAIN CONTRIBUTION

AOS subtypes have been proposed on the basis of clinical symptomatology, theoretical constructs, and an analogy to limb apraxia. Different possible subtypes of AOS are reviewed, along with their empirical support and limitations. Empirical evidence, particularly in the context of a progressive disease, supports the idea that AOS diagnosis may capture different underlying impairments of speech motor planning. Future research to advance our understanding of AOS should carefully consider the basis for subtype classification, and include large sample sizes to differentiate individual variability from possible subtypes.

CONCLUSIONS

Several proposed AOS subtypes have found some support in the literature. Further research is needed to determine the validity, coherence and utility of possible AOS subtypes for theoretical and clinical purposes.

Chunking of phonological units in speech sequencing

Efficient speech communication requires rapid, fluent production of phoneme sequences. To achieve this, our brains store frequently occurring subsequences as cohesive "chunks" that reduce phonological working memory load and improve motor performance. The current study used a motor-sequence learning paradigm in which the generalization of two performance gains (utterance duration and errors) from practicing novel phoneme sequences was used to infer the nature of these speech chunks. We found that performance improvements in duration from practicing syllables with non-native consonant clusters largely generalized to new syllables that contained those clusters. Practicing the whole syllable, however, resulted in larger performance gains in error rates compared to practicing just the consonant clusters. Collectively, these findings are consistent with theories of speech production that posit the consonant cluster as a fundamental unit of phonological working memory and speech sequencing as well as those positing the syllable as a fundamental unit of motor programming.

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/ → [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.

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.

How modality-specific is morphology?

Writing has long been considered to be dependent on speaking. However, modality-specific dissociations between written and spoken word production imply that word production is supported by distinct neural mechanisms in writing, which can be impaired or spared regardless of the intactness of spoken word production. Rapp et al. (2015). Modality and morphology: What we write may not be what we say. Psychological Science, 26, 892-902 documented a double dissociation where problems with regular inflections were selectively restricted to writing or speaking. We report on two English-speaking aphasic individuals who exhibit this same modality-specific dissociation of inflectional processing, replicating the original findings. We expand on Rapp et al.'s study by examining whether the dissociations observed with regular inflections extend to other morphological forms, such as derivation and irregular inflection. Results showed that the dissociation holds for derivation; however, both participants were impaired with irregular inflections in both output modalities. Implications of these findings for morphological processing and the independence of the orthographic system are discussed.

Contemporary Approaches to the Management of Post-stroke Apraxia of Speech

Apraxia of speech (AOS) is a motor speech disorder that disrupts the planning and programming of speech motor movements. In the acute stage of stroke recovery, AOS following unilateral (typically) left hemisphere stroke can occur alongside dysarthria, an impairment in speech execution and control, and/or aphasia, a higher-level impairment in language function. At this time, perceptual evaluation (the systematic, although subjective, description of speech and voice characteristics) is perhaps the only "gold standard" for differential diagnosis when it comes to motor speech disorders. This poses a challenge for speech-language pathologists charged with the evaluation of poststroke communication abilities, as distinguishing production impairments associated with AOS from those that can occur in aphasia and/or dysarthria can be difficult, especially when more than one deficit is present. Given the need for more objective, reliable methods to identify and diagnose AOS, several studies have turned to acoustic evaluation and neuroimaging to supplement clinical assessment. This article focuses on these recent advances. Studies investigating acoustic evaluation of AOS will be reviewed, as well as those that have considered the extent that neuroimaging can guide clinical decision making. Developments in the treatment of AOS will also be discussed. Although more research is needed regarding the use of these methods in everyday clinical practice, the studies reviewed here show promise as emerging tools for the management of AOS.