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.

Examining speech motor planning difficulties in apraxia of speech and aphasia via the sequential production of phonetically similar words.

This study investigated the underlying nature of apraxia of speech (AOS) by testing two competing hypotheses. The Reduced Buffer Capacity Hypothesis argues that people with AOS can plan speech only one syllable at a time Rogers and Storkel [1999. Planning speech one syllable at a time: The reduced buffer capacity hypothesis in apraxia of speech. Aphasiology, 13(9-11), 793-805. https://doi.org/10.1080/026870399401885]. The Program Retrieval Deficit Hypothesis states that selecting a motor programme is difficult in face of competition from other simultaneously activated programmes Mailend and Maas [2013. Speech motor programming in apraxia of speech: Evidence from a delayed picture-word interference task. American Journal of Speech-Language Pathology, 22(2), S380-S396. https://doi.org/10.1044/1058-0360(2013/12-0101)]. Speakers with AOS and aphasia, aphasia without AOS, and unimpaired controls were asked to prepare and hold a two-word utterance until a go-signal prompted a spoken response. Phonetic similarity between target words was manipulated. Speakers with AOS had longer reaction times in conditions with two similar words compared to two identical words. The Control and the Aphasia group did not show this effect. These results suggest that speakers with AOS need additional processing time to retrieve target words when multiple motor programmes are simultaneously activated.

Reliability of the Test of Integrated Language and Literacy Skills (TILLS).

BACKGROUND: As new standardized tests become commercially available, it is critical that clinicians have access to the information about a test's psychometric properties, including aspects of reliability. AIMS: The purpose of the three studies reported in this article was to investigate the reliability of a new test, the Test of Integrated Language and Literacy Skills (TILLS), with consideration of both internal and external sources of measurement error. METHODS & PROCEDURES: The TILLS was administered to children aged 6;0-18;11 years. The participants varied in terms of their language and literacy skills and included children with typical language development as well as those diagnosed with language or learning disability. The sample of children also varied in terms of their racial and socioeconomic backgrounds. Study 1 (N = 1056) assessed the internal consistency of TILLS calculating the coefficient omega for each subtest. Study 2 (N = 103) and Study 3 (N = 39) used the intra-class correlation coefficients to report on test-retest and inter-rater reliability respectively. OUTCOMES & RESULTS: The results indicate strong internal consistency and inter-rater reliability for all subtests of TILLS. The test-retest reliability was strong for all but one subtest, for which the intra-class correlation coefficient was in the acceptable range. CONCLUSION & IMPLICATIONS: This article provides clinicians with essential scientific information that supports the internal and external reliability of a new test of oral and written language skills, the TILLS. Information about reliability is critical for guiding the selection of an appropriate diagnostic tool amongst a number of options.

Benefit of visual speech information for word comprehension in post-stroke aphasia.

Aphasia is a language disorder that often involves speech comprehension impairments affecting communication. In face-to-face settings, speech is accompanied by mouth and facial movements, but little is known about the extent to which they benefit aphasic comprehension. This study investigated the benefit of visual information accompanying speech for word comprehension in people with aphasia (PWA) and the neuroanatomic substrates of any benefit. Thirty-six PWA and 13 neurotypical matched control participants performed a picture-word verification task in which they indicated whether a picture of an animate/inanimate object matched a subsequent word produced by an actress in a video. Stimuli were either audiovisual (with visible mouth and facial movements) or auditory-only (still picture of a silhouette) with audio being clear (unedited) or degraded (6-band noise-vocoding). We found that visual speech information was more beneficial for neurotypical participants than PWA, and more beneficial for both groups when speech was degraded. A multivariate lesion-symptom mapping analysis for the degraded speech condition showed that lesions to superior temporal gyrus, underlying insula, primary and secondary somatosensory cortices, and inferior frontal gyrus were associated with reduced benefit of audiovisual compared to auditory-only speech, suggesting that the integrity of these fronto-temporo-parietal regions may facilitate cross-modal mapping. These findings provide initial insights into our understanding of the impact of audiovisual information on comprehension in aphasia and the brain regions mediating any benefit.

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.

Speech motor planning in the context of phonetically similar words: Evidence from apraxia of speech and aphasia.

The purpose of this study was to test two competing hypotheses about the nature of the impairment in apraxia of speech (AOS). The Reduced Buffer Capacity Hypothesis argues that people with AOS can hold only one syllable at a time in the speech motor planning buffer. The Program Retrieval Deficit Hypothesis, states that people with AOS have difficulty accessing the intended motor program in the context where several motor programs are activated simultaneously. The participants included eight speakers with AOS, most of whom also had aphasia, nine speakers with aphasia without AOS, and 25 age-matched control speakers. The experimental paradigm prompted single word production following three types of primes. In most trials, prime and target were the same (e.g., bill-bill). On some trials, the initial consonant differed in one phonetic feature (e.g., bill-dill; Similar) or in all phonetic features (fill-bill; Different). The dependent measures were accuracy and reaction time. The results revealed a switch cost - longer reaction times in trials where the prime and target differed compared to trials where they were the same words - in all groups; however, the switch cost was significantly larger in the AOS group compared to the other two groups. These findings are in line with the prediction of the Program Retrieval Deficit Hypothesis and suggest that speakers with AOS have difficulty with selecting one program over another when several programs compete for selection.

Individual Versus Small Group Treatment of Morphological Errors for Children With Developmental Language Disorder.

Purpose This study examines the effects of enhanced conversational recast for treating morphological errors in preschoolers with developmental language disorder. The study assesses the effectiveness of this treatment in an individual or group ( n = 2) setting and the possible benefits of exposing a child to his or her partner's treatment target in addition to his or her own. Method Twenty children were assigned to either an individual ( n = 10) or group ( n = 10, 2 per group) condition. Each child received treatment for 1 morpheme (the target morpheme) for approximately 5 weeks. Children in the group condition had a different target from their treatment partner. Pretreatment and end treatment probes were used to compare correct usage of the target morpheme and a control morpheme. For children in the group condition, the correct usage of their treatment partner's target morpheme was also examined. Results Significant treatment effects occurred for both treatment conditions only for morphemes treated directly (target morpheme). There was no statistically significant difference between the treatment conditions at the end of treatment or at follow-up. Children receiving group treatment did not demonstrate significant gains in producing their partner's target despite hearing the target modeled during treatment. Conclusions This study provides the evidence base for enhanced conversational recast treatment in a small group setting, a treatment used frequently in school settings. Results indicate the importance of either attention to the recast or expressive practice (or both) to produce gains with this treatment. Supplemental Material https://doi.org/10.23641/asha.7859975.

Assessment of Childhood Apraxia of Speech: A Review/Tutorial of Objective Measurement Techniques.

Background With respect to the clinical criteria for diagnosing childhood apraxia of speech (commonly defined as a disorder of speech motor planning and/or programming), research has made important progress in recent years. Three segmental and suprasegmental speech characteristics-error inconsistency, lengthened and disrupted coarticulation, and inappropriate prosody-have gained wide acceptance in the literature for purposes of participant selection. However, little research has sought to empirically test the diagnostic validity of these features. One major obstacle to such empirical study is the fact that none of these features is stated in operationalized terms. Purpose This tutorial provides a structured overview of perceptual, acoustic, and articulatory measurement procedures that have been used or could be used to operationalize and assess these 3 core characteristics. Methodological details are reviewed for each procedure, along with a short overview of research results reported in the literature. Conclusion The 3 types of measurement procedures should be seen as complementary. Some characteristics are better suited to be described at the perceptual level (especially phonemic errors and prosody), others at the acoustic level (especially phonetic distortions, coarticulation, and prosody), and still others at the kinematic level (especially coarticulation, stability, and gestural coordination). The type of data collected determines, to a large extent, the interpretation that can be given regarding the underlying deficit. Comprehensive studies are needed that include more than 1 diagnostic feature and more than 1 type of measurement procedure.

Fricative Contrast and Coarticulation in Children With and Without Speech Sound Disorders.

PURPOSE: The purpose of this study was, first, to expand our understanding of typical speech development regarding segmental contrast and anticipatory coarticulation, and second, to explore the potential diagnostic utility of acoustic measures of fricative contrast and anticipatory coarticulation in children with speech sound disorders (SSD). METHOD: In a cross-sectional design, 10 adults, 17 typically developing children, and 11 children with SSD repeated carrier phrases with novel words with fricatives (/s/, /ʃ/). Dependent measures were 2 ratios derived from spectral mean, obtained from perceptually accurate tokens. Group analyses compared adults and typically developing children; individual children with SSD were compared to their respective typically developing peers. RESULTS: Typically developing children demonstrated smaller fricative acoustic contrast than adults but similar coarticulatory patterns. Three children with SSD showed smaller fricative acoustic contrast than their typically developing peers, and 2 children showed abnormal coarticulation. The 2 children with abnormal coarticulation both had a clinical diagnosis of childhood apraxia of speech; no clear pattern was evident regarding SSD subtype for smaller fricative contrast. CONCLUSIONS: Children have not reached adult-like speech motor control for fricative production by age 10 even when fricatives are perceptually accurate. Present findings also suggest that abnormal coarticulation but not reduced fricative contrast is SSD-subtype-specific. SUPPLEMENTAL MATERIALS: S1: https://doi.org/10.23641/asha.5103070. S2 and S3: https://doi.org/10.23641/asha.5106508.

Feedforward and feedback control in apraxia of speech: effects of noise masking on vowel production.

PURPOSE: This study was designed to test two hypotheses about apraxia of speech (AOS) derived from the Directions Into Velocities of Articulators (DIVA) model (Guenther et al., 2006): the feedforward system deficit hypothesis and the feedback system deficit hypothesis. METHOD: The authors used noise masking to minimize auditory feedback during speech. Six speakers with AOS and aphasia, 4 with aphasia without AOS, and 2 groups of speakers without impairment (younger and older adults) participated. Acoustic measures of vowel contrast, variability, and duration were analyzed. RESULTS: Younger, but not older, speakers without impairment showed significantly reduced vowel contrast with noise masking. Relative to older controls, the AOS group showed longer vowel durations overall (regardless of masking condition) and a greater reduction in vowel contrast under masking conditions. There were no significant differences in variability. Three of the 6 speakers with AOS demonstrated the group pattern. Speakers with aphasia without AOS did not differ from controls in contrast, duration, or variability. CONCLUSION: The greater reduction in vowel contrast with masking noise for the AOS group is consistent with the feedforward system deficit hypothesis but not with the feedback system deficit hypothesis; however, effects were small and not present in all individual speakers with AOS. Theoretical implications and alternative interpretations of these findings are discussed.

Speech motor programming in apraxia of speech: evidence from a delayed picture-word interference task.

PURPOSE: Apraxia of speech (AOS) is considered a speech motor programming impairment, but the specific nature of the impairment remains a matter of debate. This study investigated 2 hypotheses about the underlying impairment in AOS framed within the Directions Into Velocities of Articulators (DIVA; Guenther, Ghosh, & Tourville, 2006) model: The retrieval hypothesis states that access to the motor programs is impaired, and the damaged programs hypothesis states that the motor programs themselves are damaged. METHOD: The experiment used a delayed picture-word interference paradigm in which participants prepare their response and auditory distracters are presented with the go signal. The overlap between target and distracter words was manipulated (i.e., shared sounds or no shared sounds), and participants' reaction times (RTs) were measured. Participants included 5 speakers with AOS (4 with concomitant aphasia), 2 speakers with aphasia without AOS, and 9 age-matched control speakers. RESULTS: The control speakers showed no effects of distracter type or presence. The speakers with AOS had longer RTs in the distracter condition compared to the no-distracter condition. The speakers with aphasia without AOS were comparable to the control group in their overall RTs and RT pattern. CONCLUSION: Results provide preliminary support for the retrieval hypothesis, suggesting that access to motor programs may be impaired in speakers with AOS. However, the possibility that the motor programs may also be damaged cannot be ruled out.

Speech planning happens before speech execution: online reaction time methods in the study of apraxia of speech.

PURPOSE: The purpose of this article is to present an argument for the use of online reaction time (RT) methods to the study of apraxia of speech (AOS) and to review the existing small literature in this area and the contributions it has made to our fundamental understanding of speech planning (deficits) in AOS. METHOD: Following a brief description of limitations of offline perceptual methods, we provide a narrative review of various types of RT paradigms from the (speech) motor programming and psycholinguistic literatures and their (thus far limited) application with AOS. CONCLUSION: On the basis of the review of the literature, we conclude that with careful consideration of potential challenges and caveats, RT approaches hold great promise to advance our understanding of AOS, in particular with respect to the speech planning processes that generate the speech signal before initiation. A deeper understanding of the nature and time course of speech planning and its disruptions in AOS may enhance diagnosis and treatment for AOS. RESULTS: Only a handful of published studies on apraxia of speech have used reaction time methods. However, these studies have provided deeper insight into speech planning impairments in AOS based on a variety of experimental paradigms.