Acquired apraxia of speech (AOS) is a treatable neurologic, sensorimotor speech disorder. The primary clinical characteristics considered necessary for the diagnosis of AOS include: 1) a slow rate of speech resulting in lengthened sound segments and intersegment durations, 2) speech-sound errors such as sound distortions and/or distorted sound substitutions, 3) errors that are relatively consistent in type (i.e., distortion) and location (i.e., within a word), and 4) disturbed prosody (McNeil et al., 2009). Other speech behaviors that frequently occur with AOS include articulatory groping, perseverative errors, increased errors with increased word length, and speech initiation difficulties (McNeil et al., 2009). These behaviors, however, cannot be used to differentially diagnose AOS because they may also occur with other communication disorders, such as phonemic paraphasia.    

The severity of AOS varies from minor sound distortions to an inability to produce speech. Stroke is the most frequent etiology resulting in AOS (Duffy, 2005). AOS is linked to cortical and/or subcortical damage in the language-dominant hemisphere of the brain (McNeil et al., 2009), but researchers are still uncertain about the specific brain regions involved in AOS (Hillis et al., 2004; Ogar et al., 2006). Although AOS is most often associated with a neurological event of sudden onset, progressive apraxia of speech has been reported in individuals with a diagnosis of motor neuron disease (Duffy, 2006; Duffy et al., 2007).

There are limited data regarding the prevalence of the disorder, but Duffy (2005) reported that AOS was the primary communication disorder in 7.6% of 6,101cases. These data reflect individuals evaluated at Mayo Clinic from 1987–1990 and 1993–2001 who were diagnosed with a neurological motor-speech disorder as the primary communication disorder when more than one disorder was present (i.e., primary indicates the more severe disorder in terms of impairment). As a secondary communication disorder, AOS co-occurs even more frequently with aphasia (i.e., when aphasia is the primary disorder; Duffy, 2005). AOS rarely occurs in its "pure" form (i.e., as the primary disorder in the absence of a secondary disorder). 

Published reports of treatment for AOS first appeared in 1973 with the influential treatment investigation conducted by Rosenbek and colleagues examining the effects of their eight-step task continuum (Rosenbek et al., 1973). Since that initial investigation, there has been substantial growth in the literature documenting the benefits of AOS treatment.

Evidence Base for AOS Treatment 

A recent systematic review of the AOS treatment literature was conducted by the Apraxia of Speech Treatment Guidelines Committee of the Academy of Neurologic Communication Disorders and Sciences (ANCDS) for the purpose of developing AOS treatment guidelines (Wambaugh et al., 2006a, 2006b). This review involved an extensive, objective evaluation of the existing English-language AOS treatment literature published through 2003. The AOS treatment guidelines report evaluated the 59 studies and provided a detailed summary of each treatment study (see evidence table; Wambaugh et al., 2006b). The committee found that the treatments evaluated in the report generally fell into one of four categories: 1) articulatory-kinematic treatments, 2) rate/rhythm control treatments, 3) intersystemic facilitation/reorganization treatments, and 4) alternative and augmentative communication (AAC) approaches.

The AOS report concluded that the existing evidence base for AOS treatment indicates that individuals with AOS can benefit from treatment even when AOS is considered chronic (Wambaugh et al., 2006b).

Wambaugh and Mauszycki (2010b) recently reviewed 74 investigations in the AOS treatment literature (15 additional treatment investigations were identified that had been conducted since the completion of the AOS guidelines). The purpose of this review was to describe AOS treatment outcome measures using the context of the World Health Organization's International Classification of Functioning, Disability, and Health (ICF; WHO, 2001). The World Health Organization's ICF offers a conceptual framework and uniform language for describing human functioning and disability, including implications for developing and measuring clinical treatments and outcomes (Eadies et al., 2006).

Findings revealed that the majority of outcome measures reported in the AOS treatment literature corresponded to the ICF's level of "Body Function"; most outcomes reflected "articulation function"
and/or "fluency and rhythm of speech function." Only a limited number of studies included outcome measures that addressed other concepts included in the ICF's "Activity/Participation" category. The investigators concluded that there is a need for development of functional communication outcome measures that are appropriate for persons with AOS.

Systematic reviews have indicated that persons with AOS can benefit from treatment, but little is known about the impact of treatment on functional communication. The majority of objective evidence supporting treatment for AOS addresses articulatory-kinematic therapeutic approaches (Wambaugh et al., 2006b). Recent research has suggested that rate/rhythm treatments also may improve articulation in AOS and may provide additional benefits beyond articulatory/kinematic approaches (Brendel & Ziegler, 2008). The other two general treatment approaches—intersystemic facilitation/reorganization and alternative/augmentative communication—identified in the recent review of the AOS treatment literature (Wambaugh et al., 2006a, 2006b) uncovered a limited number of treatment studies for each approach. Consequently, findings have been inconclusive in determining possible treatment effects for these approaches.

Articulatory-Kinematic Treatments 

More than half of the treatment investigations in the AOS treatment evidence base have used an articulatory-kinematic-based approach. The rationale and the treatment techniques used in these investigations have focused on improving spatial and temporal aspects of speech production. Typically, these investigations have employed a combination of repeated, motoric practice; modeling-repetition; integral stimulation; and articulatory cueing.

Motoric Practice 

Repeated, motoric practice has been a primary component of most articulatory-kinematic treatment investigations. Repeated practice is considered to be an important aspect of treatment and its use is supported by findings in limb motor-learning literature (Schmidt & Lee, 2005), which recently have been applied to speech learning/relearning, principles of experience-dependent neural plasticity involving rehabilitation following stroke or brain injury (Kleim & Jones, 2008), and neural models of speech production in the early stages of speech development and acquiring speech sounds (Guenther, 2006). Repeated practice with limited verbal feedback recently has been shown to result in improved articulation with persons with chronic AOS and aphasia without any other treatment (Wambaugh et al., 2010).

Modeling-Repetition 

Modeling-repetition is a component of many articulatory-kinematic treatments. A variation is integral stimulation, in which the patient is instructed to "watch me, listen to me, and say it with me" (Rosenbek et al., 1973; Wambaugh et al., 1998, 1999, 2010a). Integral stimulation aims to bring to conscious awareness the "look" and "sound" of the target movement in conjunction with simultaneous practice.

Articulatory Cueing 

A technique frequently incorporated into articulatory-kinematic treatments is articulatory cueing. This technique increases awareness and actualization of articulatory postures and/or movements and may take the form of phonetic placement or phonetic derivation. Phonetic placement cues use descriptions of what (which articulators), where (positioning or location), and how (manner, voicing) sounds are made, using descriptions from verbal explanations, visual modeling, drawings, and/or physical cueing by the clinician of the orofacial musculature (Square et al., 2001; Wambaugh et al. 1998, 1999, 2010a). Phonetic derivation is a shaping technique that builds upon the articulatory or orofacial skills in the patient's repertoire (Knock et al., 2000; Wertz et al., 1984). A clinician using this technique provides instructions or models how to modify existing speech or non-speech movements to produce the intended target.

Instrumental approaches for providing supplemental feedback have received increasing attention as articulatory-kinematic treatments for AOS. Electromagnetic articulography (EMA; Katz et al., 1999, 2007; McNeil et al., 2007), electropalatography (EPG; Howard & Varley, 1995), and spectrographic displays (Ballard et al., 2007) have been used with speakers with AOS. The converging evidence from these different technologies suggests that instrumentally generated feedback may benefit speakers with AOS. These approaches require additional equipment and expertise that may limit their appeal to clinicians, but EPG and spectrographic analysis have become relatively accessible in terms of cost and usage. 

Articulatory-kinematic treatments usually include a combination of techniques. For example, Sound Production Treatment (SPT; Wambaugh et al., 1998, 2010a; Wambaugh & Nessler, 2004) uses a response-contingent hierarchy that includes the following steps: 1) verbal modeling/repetition, 2) graphemic cue plus modeling/repetition, 3) integral stimulation, and 4) articulatory placement instruction. The hierarchy is applied to one target item at a time, with steps applied only as needed.

Little research has addressed the effects of different articulatory-kinematic techniques or components of treatment. There is insufficient evidence to conclude that any one technique or combination of techniques is superior to another. Treatments such as SPT or Prompts for Restructuring Oral and Muscular Phonetic Targets (PROMPT; Square et al., 2001) that have been studied repeatedly may have somewhat predictable outcomes. Although other articulatory-kinematic treatments (including those developed by clinicians) are likely to have positive effects, the clinician must collect practice-based evidence to document patient outcomes with all AOS treatments.

Outcome Measures 

In most articulatory-kinematic investigations, the effects of treatment were measured in probe sessions (measures of treated behaviors collected prior to administration of treatment or treatment session over the course of an investigation). The outcome measure for the majority of articulatory-kinematic investigations has been articulatory accuracy, which is considered to reflect "articulatory function" under the ICF framework. Perceptual evaluation via phonetic transcription, rating scale, and/or descriptors of accuracy were most frequently used to assess speech production.

As noted by the AOS Treatment Guidelines Committee, a substantial body of evidence supports the use of articulatory-kinematic treatments for AOS (Wambaugh et al., 2006b). Within the context of the patient's preference, the committee recommended that "articulatory kinematic approaches be utilized with individuals with moderate-to-severe AOS who demonstrate disrupted communication due to disturbances in the spatial and temporal aspects of speech production" (Wambaugh et al., 2006b p.lxii).

Rate/Rhythm Control Treatment 

Rate- and rhythm-control treatments, such as metronomic pacing and metrical pacing, involve manipulation of rate and/or rhythm to improve speech production or reduce symptoms of AOS. Nine investigations have examined the effects of rate- and rhythm-control treatments (for descriptions, see Wambaugh et al., 2006b; Wambaugh & Mauszcyki, 2010b). A basic assumption of such approaches is that AOS involves a disruption in the timing of speech production. There are three proposed underlying mechanisms in which rate and rhythm control treatments are considered to influence AOS. However, the underlying mechanism or mechanisms responsible for the behavioral changes (i.e., improved articulation, increased fluency) associated with this treatment approach are not well understood and remain speculative.

Rhythmic-control treatments usually have involved slowing the rate of speech production in speakers who already exhibit a reduced production rate. The reduced rate is believed to allow additional time for speakers to reach their intended articulatory targets as well as to process sensorimotor feedback involved in speech production. The use of a rhythmic source may re-establish internal oscillatory mechanisms suspected of being involved in speech production (Dworkin & Abkarian, 1996). Additionally, the use of rate and rhythm controls may serve to focus the speaker's attention either on increasing the accuracy of speech production (Dworkin et al., 1988) or away from speech production (Brendel et al., 2000).  

Metronomic Pacing 

In metronomic pacing, the speaker produces speech at the rate of one syllable or movement per beat of a metronome. Typically, the beat has been set at a rate significantly slower than the speaker's habitual rate of speech (Dworkin et al., 1988, 1996; Wambaugh & Martinez, 2000). Behaviors targeted with this approach have varied from non-speech tasks (e.g., tongue movements) to speech tasks of varying lengths (syllable to phrase-level productions). The amount of clinical instruction and participation also varied among investigations from minimal clinician involvement to clinician modeling with gradual fading.  Hand-tapping—requiring speakers to tap along to the beat of the metronome—may be used in conjunction with metronomic pacing (Mauszycki & Wambaugh, 2008; Wambaugh & Martinez, 2000).

Metrical Pacing 

Metrical pacing is similar to metronomic pacing, but the natural rhythm or prosody of the target utterances is maintained (Brendel & Ziegler, 2008; Brendel et al., 2000). Treatment involves computer-generated pacing tones for each utterance that maintain the natural rhythm of the utterance regardless of rate of production. This treatment also includes hand-tapping, choral speaking, and varying levels of clinician participation.

Metronomic pacing and metrical pacing both entail repeated practice of target utterances in time to the pacing mechanism. In one treatment protocol (Wambaugh & Martinez, 2000), productions of multisyllabic words were practiced to the beat of the metronome set to reduce the participant's rate of production by approximately 50% in comparison to his typical productions. The treatment included clinician modeling, unison production, and hand-tapping, followed by participant production without assistance. Clinician participation was faded across levels of treatment. In addition, rate was gradually increased and syncopation was added to facilitate "naturalness" of productions.

Metronomic pacing and metrical pacing have resulted in improved articulation for speakers with AOS, but have not been directly compared experimentally. Metrical pacing is theoretically appealing because the natural rhythm of the utterance is preserved. In terms of clinical application, however, metrical pacing would be more labor-intensive than metronomic pacing. With metrical pacing, "metrical templates" must be developed for each target utterance based upon syllable-onset times derived from waveforms of the utterances. A computer program also must be available for implementation of the templates at different rates.

Other methods for modifying rate/rhythm as treatment for AOS have received limited study. Such methods include finger-counting (Simmons, 1978), pacing board practice (McHenry & Wilson, 1994), and computerized pacing of oral reading (Southwood, 1987).

Outcome Measures 

As with articulatory-kinematic treatments, outcome measures have focused on "Body Function." Accuracy of articulation, or production of sound errors, has been measured in several investigations (Brendel & Ziegler, 2008; Wambaugh & Martinez, 2000). Treatment resulted in positive changes in articulation despite no direct focus on articulation. Other outcome measures have included measures of dysfluency (Brendel & Ziegler, 2008) and ratings of the acceptability of productions [i.e., presence or absence of AOS symptoms in speech and non-speech behaviors that were treated (Dworkin & Abkarian, 1996; Dworkin et al., 1988)]. In addition, various durational measures have been studied (Brendel & Ziegler, 2008; Mauszycki & Wambaugh, 2008). 

Despite the advancements in understanding the effects of various treatment approaches for AOS, there are limits to the data available to help guide clinicians in selecting a specific treatment for a patient. The prediction of patient outcomes also is limited for most AOS treatment approaches, especially with respect to functional communication. As suggested by Wambaugh and colleagues (2006b), treatment for individuals with AOS should include integration of objective treatment evidence, clinical knowledge and experience, theoretical rationale, and consideration of the patient's needs and treatment goals.