Treatment for Childhood Apraxia of Speech: Past, Present, and Future.

PURPOSE: The purposes of this review article were to provide an introduction to and "bird's-eye" overview of the current evidence base for treatment of childhood apraxia of speech (CAS), identify some gaps and trends in this rapidly growing literature, and formulate some future research directions, in order to advance the evidence base and clinical practice for children with CAS. METHOD: Following a brief introduction outlining important concepts, a narrative review of the CAS treatment literature is provided, and trends and future directions are identified based on this review. The review is organized around four fundamental treatment research questions: (a) "Does Treatment X work?", (b) "Does Treatment X work better than Treatment Y?", (c) "For whom does Treatment X work?", and (d) "What does 'work' mean, anyway?" RESULTS: A wide range of CAS treatments with varying degrees of evidence for efficacy exists. Research is beginning to emerge that compares different treatments and seeks to determine optimal treatment parameters. Few studies to date have explored child-level predictors of treatment response, and the evidence base currently is limited in scope with respect to populations and outcomes studied. CONCLUSIONS: A growing evidence base supports the efficacy of a number of treatments for CAS. However, many important gaps in the literature were identified that warrant redoubled and sustained research attention. Research is beginning to emerge that addresses treatment optimization, comparison, candidacy, and outcomes. Suggestions for future research are offered, and the concept of a hypothesized pathway was applied to CAS to illustrate how components of an intervention can effect change in a clinical goal and can help guide development and refinement of treatments for children with CAS.

A Comparison of Sound Production Treatment and Metrical Pacing Therapy for Apraxia of Speech: A Single-Case Experimental Design.

PURPOSE: The purpose of this investigation was to compare the effects of two specific treatment protocols for acquired apraxia of speech (AOS): Sound Production Treatment (SPT) and Metrical Pacing Therapy (MPT), and to examine changes in communicative participation. METHOD: Four speakers with chronic AOS and aphasia were each administered SPT and MPT in a replicated crossover design (ABACA/ACABA) with nonconcurrent multiple baselines across participants and behaviors. Treatment outcomes were compared with respect to whole word correctness (WWC) for treated and untreated multisyllabic word targets. Speech intelligibility was assessed using the Chapel Hill Multilingual Intelligibility Test, and communicative participation was measured using the Communicative Participation Item Bank at baseline, washout, and follow-up phases. RESULTS: Three of the four participants experienced statistically significant improvements in WWC with SPT, and three of the four participants with MPT. Based on a priori criteria, three participants demonstrated relatively greater benefit from SPT and one participant demonstrated relatively greater benefit from MPT. There were measurable improvements in intelligibility following SPT for three of the four participants. Only one participant in this investigation reported a significant change in communicative participation, and only following MPT. CONCLUSIONS: This study demonstrated that individuals in the chronic stages of AOS can benefit from both SPT and MPT, corroborating prior research on articulatory kinematic and rate and/or rhythm control treatment approaches. It contributes a comparison of two protocols for AOS with respect to whole word targets, intelligibility, and individual self-report of communicative participation changes. More participants showed a relative advantage of SPT over MPT. One individual reported communicative participation improvement after MPT. SUPPLEMENTAL MATERIAL: https://doi.org/10.23641/asha.23971929.

How to cut the pie is no piece of cake: Toward a process-oriented approach to assessment and diagnosis of speech sound disorders.

BACKGROUND: 'Speech sound disorder' is an umbrella term that encompasses dysarthria, articulation disorders, childhood apraxia of speech and phonological disorders. However, differential diagnosis between these disorders is a persistent challenge in speech pathology, as many diagnostic procedures use symptom clusters instead of identifying an origin of breakdown in the speech and language system. AIMS: This article reviews typical and disordered speech through the lens of two well-developed models of production-one focused on phonological encoding and one focused on speech motor planning. We illustrate potential breakdown locations within these models that may relate to childhood apraxia of speech and phonological disorders. MAIN CONTRIBUTION: This paper presents an overview of an approach to conceptualisation of speech sound disorders that is grounded in current models of speech production and emphasises consideration of underlying processes. The paper also sketches a research agenda for the development of valid, reliable and clinically feasible assessment protocols for children with speech sound disorders. CONCLUSION: The process-oriented approach outlined here is in the early stages of development but holds promise for developing a more detailed and comprehensive understanding of, and assessment protocols for speech sound disorders that go beyond broad diagnostic labels based on error analysis. Directions for future research are discussed. WHAT THIS PAPER ADDS: What is already known on the subject Speech sound disorders (SSD) are heterogeneous, and there is agreement that some children have a phonological impairment (phonological disorders, PD) whereas others have an impairment of speech motor planning (childhood apraxia of speech, CAS). There is also recognition that speech production involves multiple processes, and several approaches to the assessment and diagnosis of SSD have been proposed. What this paper adds to existing knowledge This paper provides a more detailed conceptualisation of potential impairments in children with SSD that is grounded in current models of speech production and encourages greater consideration of underlying processes. The paper illustrates this approach and provides guidance for further development. One consequence of this perspective is the notion that broad diagnostic category labels (PD, CAS) may each comprise different subtypes or profiles depending on the processes that are affected. What are the potential or actual clinical implications of this work? Although the approach is in the early stages of development and no comprehensive validated set of tasks and measures is available to assess all processes, clinicians may find the conceptualisation of different underlying processes and the notion of potential subtypes within PD and CAS informative when evaluating SSD. In addition, this perspective discourages either/or thinking (PD or CAS) and instead encourages consideration of the possibility that children may have different combinations of impairments at different processing stages.

Neural Changes in Children With Residual Speech Sound Disorder After Ultrasound Biofeedback Speech Therapy.

PURPOSE: Children with residual speech sound disorders (RSSD) have shown differences in neural function for speech production, as compared to their typical peers; however, information about how these differences may change over time and relative to speech therapy is needed. To address this gap, we used functional magnetic resonance imaging (fMRI) to examine functional activation and connectivity on adaptations of the syllable repetition task (SRT-Early Sounds and SRT-Late Sounds) in children with RSSD before and after a speech therapy program. METHOD: Sixteen children with RSSD completed an fMRI experiment before (Time 1) and after (Time 2) a speech therapy program with ultrasound visual feedback for /ɹ/ misarticulation. Progress in therapy was measured via perceptual ratings of productions of untreated /ɹ/ word probes. To control for practice effects and developmental change in patterns of activation and connectivity, 17 children with typical speech development (TD) completed the fMRI at Time 1 and Time 2. Functional activation was analyzed using a region-of-interest approach and functional connectivity was analyzed using a seed-to-voxel approach. RESULTS: Children with RSSD showed a range of responses to therapy. After correcting for multiple comparisons, we did not observe any statistically significant cross-sectional differences or longitudinal changes in functional activation. A negative relationship between therapy effect size and functional activation in the left visual association cortex was on the SRT-Late Sounds after therapy, but it did not survive correction for multiple comparisons. Significant longitudinal changes in functional connectivity were observed for the RSSD group on SRT-Early Sounds and SRT-Late Sounds, as well as for the TD group on the SRT-Early Sounds. RSSD and TD groups showed connectivity differences near the left insula on the SRT-Late Sounds at Time 2. CONCLUSION: RSSD and treatment with ultrasound visual feedback may thus be associated with neural differences in speech motor and visual association processes recruited for speech production.

Self-Reported Communication Attitudes of Children With Childhood Apraxia of Speech: An Exploratory Study.

PURPOSE: Much of the research literature on childhood apraxia of speech (CAS) has focused on understanding, diagnosing, and treating the impairment, rather than examining its functional effect on children's daily lives. This study focuses on the Personal Factors component of the World Health Organization International Classification of Functioning, Disability and Health-Children and Youth Version Framework. Specifically, the purpose was to examine the self-reported communication attitudes of children with CAS. METHOD: Two validated communication attitude questionnaires were administered to 12 children with CAS enrolled in an intensive speech-focused intervention (age range: 4-10 years old). Children's scores were compared to the questionnaires' typically developing norms. Descriptive analyses explored relationships between communication attitude and CAS severity, caregiver perceptions of communicative participation, frustration ratings during therapy, and change in communication attitude over a brief time. RESULTS: Older (ages 6-10 years) but not younger (ages 4-5;11 [years;months]) children with CAS were more likely to have negative attitudes about their speech. No clear relationships were observed between communication attitudes and caregiver perceptions of communicative participation; small positive relationships were observed between communication attitude and frustration during therapy. For the younger children, there was also a relationship with CAS severity. For most children, no change in communication attitude was observed over a brief period, though one child appeared to develop more negative and one appeared to develop more positive attitudes. CONCLUSIONS: These initial findings suggest that older children with CAS may be at greater risk for negative communication attitudes than their peers without CAS. The findings also highlight the need to include more child self-report measures in research. Further implications for CAS assessment and intervention are discussed. SUPPLEMENTAL MATERIAL: https://doi.org/10.23641/asha.21834432.

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.

A Randomized Controlled Trial of the Effects of Group Conversation Treatment on Monologic Discourse in Aphasia.

PURPOSE: Evidence has shown that group conversation treatment may improve communication and reduce social isolation for people with aphasia. However, little is known about the impact of conversation group treatment on measures of discourse. This project explored the impact of conversation treatment on measures of monologic discourse. METHOD: In this randomized controlled trial, 48 participants with chronic aphasia were randomly assigned to dyadic, large group, or control conditions. Conversation group treatment was provided for 1 hr, twice per week, for 10 weeks. Discourse samples were collected and coded at pretreatment, posttreatment, and 6-week maintenance. There were three narrative tasks: (a) Comprehensive Aphasia Test (CAT) picture description, (b) Cat Rescue Picture, and (c) Cinderella retell. All narratives were coded using the percent correct information units (percent CIUs), the CAT standardized narrative analysis method, and the complete utterance (CU) method. RESULTS: No significant changes were observed on percent CIU, which was the primary outcome measure. The treated groups demonstrated improvement on aspects of the CU method following treatment, whereas the control group did not. Significant changes were observed for other CIU measures and the CAT standardized narrative analysis in both the treated and control groups. CONCLUSIONS: The results suggest that the CU measures were more sensitive to the effects of conversation treatment in monologic discourse compared to CIU and CAT measures. Changes were more common in absolute rather than relative values, suggesting that conversation treatment impacts the overall amount of language produced rather than efficiency of production.

Autism-Centered Therapy for Childhood Apraxia of Speech (ACT4CAS): A Single-Case Experimental Design Study.

Purpose A subset of children with autism spectrum disorder (ASD) has speech sound disorders, including childhood apraxia of speech (CAS). To date, virtually all speech treatment studies consider ASD an exclusionary criterion, resulting in little scientific evidence for treatment of CAS for children who also have ASD. This study proposes and tests a novel approach, Autism-Centered Therapy for Childhood Apraxia of Speech (ACT4CAS), as a theoretically and clinically informed speech treatment option for this population. Method Using a multiple-baseline design within and across participants, three children with co-occurring ASD and CAS received 11-18 treatment sessions. Treatment targets were individually designed and matched with untreated control words. Probes were administered at the start of each session to assess speech production accuracy perceptually. Changes in production accuracy were examined through visual inspection and quantified with effect sizes. Results Findings were mixed, with one child showing significant gains for half of the treated targets at follow-up and two children showing no clear improvement. Conclusions Preliminary evidence suggests potentially positive treatment effects for ACT4CAS when implemented as intended, although treatment intensity and disorder severity likely influence treatment outcome. Replication and comparison of ACT4CAS to other speech treatments is needed. Supplemental Material https://doi.org/10.23641/asha.14110445.

Neuroimaging of the Syllable Repetition Task in Children With Residual Speech Sound Disorder.

Purpose This study investigated phonological and speech motor neural networks in children with residual speech sound disorder (RSSD) during an overt Syllable Repetition Task (SRT). Method Sixteen children with RSSD with /ɹ/ errors (6F [female]; ages 8;0-12;6 [years;months]) and 16 children with typically developing speech (TD; 8F; ages 8;5-13;7) completed a functional magnetic resonance imaging experiment. Children performed the SRT ("SRT-Early Sounds") with the phonemes /b, d, m, n, ɑ/ and an adapted version ("SRT-Late Sounds") with the phonemes /ɹ, s, l, tʃ, ɑ/. We compared the functional activation and transcribed production accuracy of the RSSD and TD groups during both conditions. Expected errors were not scored as inaccurate. Results No between-group or within-group differences in repetition accuracy were found on the SRT-Early Sounds or SRT-Late Sounds tasks at any syllable sequence length. On a first-level analysis of the tasks, the TD group showed expected patterns of activation for both the SRT-Early Sounds and SRT-Late Sounds, including activation in the left primary motor cortex, left premotor cortex, bilateral anterior cingulate, bilateral primary auditory cortex, bilateral superior temporal gyrus, and bilateral insula. The RSSD group showed similar activation when correcting for multiple comparisons. In further exploratory analyses, we observed the following subthreshold patterns: (a) On the SRT-Early Sounds, greater activation was found in the left premotor cortex for the RSSD group, while greater activation was found in the left cerebellum for the TD group; (b) on the SRT-Late Sounds, a small area of greater activation was found in the right cerebellum for the RSSD group. No within-group functional differences were observed (SRT-Early Sounds vs. SRT-Late Sounds) for either group. Conclusions Performance was similar between groups, and likewise, we found that functional activation did not differ. Observed functional differences in previous studies may reflect differences in task performance, rather than fundamental differences in neural mechanisms for syllable repetition.

Differential Diagnosis of Childhood Apraxia of Speech Compared to Other Speech Sound Disorders: A Systematic Review.

Purpose The aim of this study was to determine the discriminative features that might contribute to differentiation of childhood apraxia of speech (CAS) from other speech sound disorders (SSDs). Method A comprehensive literature search was conducted for articles or doctoral dissertations that included ≥ 1 child with CAS and ≥ 1 child with SSD. Of 2,071 publications screened, 53 met the criteria. Articles were assessed for (a) study design and risk of bias; (b) participant characteristics and confidence in diagnosis; and (c) discriminative perceptual, acoustic, or kinematic measures. A criterion was used to identify promising studies: American Academy of Neurology study design (Class III+), replicable participant descriptions and adequate confidence in diagnosis (≥ 3), and ≥ 1 discriminative and reliable measure. Results Over 75% of studies were retrospective, case-control designs and/or assessed English-speaking children. Many studies did not fully describe study design and quality. No studies met the Class I (highest) quality rating according to American Academy of Neurology guidelines. CAS was mostly compared to speech delay/phonological disorder. Only six studies had diagnostic confidence ratings of 1 (best). Twenty-six studies reported discriminative perceptual measures, 14 reported discriminative acoustic markers, and four reported discriminative kinematic markers. Measures were diverse, and only two studies directly replicated previous findings. Overall, seven studies met the quality criteria, and another eight nearly met the study criteria to warrant further investigation. Conclusions There are no studies of the highest diagnostic quality. There are 15 studies that can contribute to further diagnostic efforts discriminating CAS from other SSDs. Future research should utilize careful diagnostic design, support replication, and adhere to standard reporting guidelines. Supplemental Material https://doi.org/10.23641/asha.13158149.

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.

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.

Testing hypotheses about the underlying deficit of apraxia of speech through computational neural modelling with the DIVA model.

Purpose: A recent behavioural experiment featuring a noise masking paradigm suggests that Apraxia of Speech (AOS) reflects a disruption of feedforward control, whereas feedback control is spared and plays a more prominent role in achieving and maintaining segmental contrasts. The present study set out to validate the interpretation of AOS as a possible feedforward impairment using computational neural modelling with the DIVA (Directions Into Velocities of Articulators) model.Method: In a series of computational simulations with the DIVA model featuring a noise-masking paradigm mimicking the behavioural experiment, we investigated the effect of a feedforward, feedback, feedforward + feedback, and an upper motor neuron dysarthria impairment on average vowel spacing and dispersion in the production of six/bVt/speech targets.Result: The simulation results indicate that the output of the model with the simulated feedforward deficit resembled the group findings for the human speakers with AOS best.Conclusion: These results provide support to the interpretation of the human observations, corroborating the notion that AOS can be conceptualised as a deficit in feedforward control.

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.

Bang for Your Buck: A Single-Case Experimental Design Study of Practice Amount and Distribution in Treatment for Childhood Apraxia of Speech.

Purpose The aim of this study was to examine 2 aspects of treatment intensity in treatment for childhood apraxia of speech (CAS): practice amount and practice distribution. Method Using an alternating-treatments single-subject design with multiple baselines, we compared high versus low amount of practice, and massed versus distributed practice, in 6 children with CAS. Conditions were manipulated in the context of integral stimulation treatment. Changes in perceptual accuracy, scored by blinded analysts, were quantified with effect sizes. Results Four children showed an advantage for high amount of practice, 1 showed an opposite effect, and 1 showed no condition difference. For distribution, 4 children showed a clear advantage for massed over distributed practice post treatment; 1 showed an opposite pattern, and 1 showed no clear difference. Follow-up revealed a similar pattern. All children demonstrated treatment effects (larger gains for treated than untreated items). Conclusions High practice amount and massed practice were associated with more robust speech motor learning in most children with CAS, compared to low amount and distributed practice, respectively. Variation in effects across children warrants further research to determine factors that predict optimal treatment conditions. Finally, this study adds to the evidence base supporting the efficacy of integral stimulation treatment for CAS. Supplemental Material https://doi.org/10.23641/asha.9630599.

A Psycholinguistic Framework for Diagnosis and Treatment Planning of Developmental Speech Disorders.

BACKGROUND: Differential diagnosis and treatment planning of developmental speech disorders (DSD) remains a major challenge in paediatric speech-language pathology. Different classification systems exist, in which subtypes are differentiated based on their theoretical cause and in which the definitions generally refer to speech production processes. Accordingly, various intervention methods have been developed aiming at different parts of the speech production process. Diagnostic classification in these systems, however, is primarily based on a description of behavioural speech symptoms rather than on underlying deficits. PURPOSE: In this paper, we present a process-oriented approach to diagnosis and treatment planning of DSD. Our framework comprises two general diagnostic categories: developmental delay and developmental disorder. Within these categories, treatment goals/targets and treatment methods are formulated at the level of processes and rules/representations. CONCLUSION: A process-oriented approach to diagnosis and treatment planning holds important advantages, offering direct leads for treatment aimed at the underlying impairment, tailored to the specific needs of the individual and adjusted to the developmental trajectory.

Two to Tango or the More the Merrier? A Randomized Controlled Trial of the Effects of Group Size in Aphasia Conversation Treatment on Standardized Tests.

Purpose Group conversation treatment has the potential to improve communication and reduce social isolation for people with aphasia. This project examined how 2 conflicting hypotheses-treatment dosage and group dynamics-affect treatment outcomes. Method Forty-eight participants with chronic aphasia were randomly assigned to either a dyad, a large group, or a delayed control group. Conversation group treatment was provided for an hour, twice per week, for 10 weeks. Individual goals were developed by each participant and addressed in the context of thematically oriented conversation treatment. Standardized testing across language domains was completed pretreatment (Time 1), posttreatment (Time 2), at a 6-week maintenance point (Time 3), and at 11-month follow-up for the experimental groups. Results Treatment groups showed greater changes on standardized measures than the control group posttreatment. Dyads showed the most changes on measures of language impairment, whereas changes on the self-reported functional communication measure (Aphasia Communication Outcome Measure) and connected speech task only showed significant changes in the large group. Conclusions This randomized controlled trial on conversation treatment indicated that both treatment groups-but not the delayed control group-showed significant changes on standardized tests. Hence, conversation treatment is associated with changes in measures of language impairment and quality of life. Dyads showed the most changes on measures of language impairment, whereas changes on the functional communication measure (Aphasia Communication Outcome Measure) and discourse production only showed significant changes in the large group. Thus, group size may be associated with effects on different types of outcome measures.

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.