Enhancing Articulatory Kinematics at the Segmental Level

Several facilitative techniques have been recommended to enhance postural shaping and phasing of the articulators at the segmental and syllable levels and have been described in detail by Wertz, LaPointe, and Rosenbek (1984). These techniques include (1) phonetic derivation, which refers to the shaping of speech sounds based on corresponding nonspeech postures, (2) progressive approximation, which involves the gradual shaping of targeted speech segments from other speech segments, (3) integral stimulation and phonetic placement, which employ visual models, verbal descriptions and physical manipulations to achieve the desired articulatory posture, and movement, and (4) minimal pairs contrasts, which requires patients to produce syllable or word pairs in which one member of the pair differs minimally with respect to manner, place, or voicing features from the other member of the pair.

Several early studies examined, in isolation or in various combinations, the effects of these facilitative techniques on speech production, and reported positive treatment responses (Rosenbek et al., 1973; Holtzapple and Marshall, 1977; Deal and Florance, 1978; Thompson and Young, 1983; LaPointe, 1984; Wertz, 1984). However, most of these studies suffered from methodological limitations, including inadequate subject selection criteria, nonreplicable treatment protocols, and pre-experimental research designs, which precluded firm conclusions regarding the validity and generalizability of the reported treatment effects. Contemporary investigations have addressed these methodological shortcomings and support earlier findings regarding the positive effects of treatment techniques aimed at enhancing articulatory kinematic aspects of speech at the sound, syllable, and word levels.

Specifically, in a series of investigations using single-subject experimental designs Wambaugh and colleagues examined the effects of a procedurally explicit treatment protocol employing the facilitative techniques of integral stimulation, phonetic placement, and minimal pair contrasts in 11 well-described subjects with AOS (Wambaugh et al., 1996, 1998, 1999; Wambaugh, West, and Doyle, 1998; Wambaugh and Cort, 1998; Wambaugh, 2000). These studies revealed positive treatment effects on targeted phonemes in trained and untrained words for all subjects across all studies, and positive maintenance effects of targeted sounds at 6 weeks post-treatment. In addition, two subjects showed positive generalization of trained sounds to novel stimulus contexts (i.e., untrained phrases), and one subject showed positive generalization to untrained sounds within the same sound class (voiced stops). These results provide initial experimental evidence that treatment strategies designed to enhance postural shaping and phasing of the articulators are efficacious in improving sound production of treated and untreated words. Further, there is limited evidence that for some patients and some sounds, generalization to untrained contexts may be expected.

Enhancing Segmental Sequencing of Longer Speech Units

Several facilitative techniques have been recommended to improve speech production in persons with AOS, based on the premise that the sequencing and coordination of movement parameters required for the production of longer speech units (and other complex motor behaviors) are governed by internal oscillatory mechanisms (Gracco, 1990) and temporal constraints (Kent and Adams, 1989). Treatment programs and tactics grounded in this framework employ techniques designed to reduce or control speech rate while enhancing the natural rhythm and stress contours of the targeted speech unit. The effects of several such specific facilitative techniques have been studied. These include metronomic pacing (Shane and Darley, 1978; Dworkin, Abkarian, and Johns, 1988; Dworkin and Abkarian, 1996; Wambaugh and Martinez, 1999), prolonged speech (Southwood, 1987), vibrotactile stimulation (Rubow et al., 1982), and intersystemic facilitation (i.e., finger counting) (Simmons, 1978). In addition, the effects of similarly motivated treatment programs, melodic intonation therapy (Sparks, 2001) and surface prompts (Square, Chumpelik, and Adams, 1985), have also been reported.

As with studies examining the effects of techniques designed to enhance articulatory kinematic aspects of speech at the segmental level, the empirical evidence supporting the facilitative effects of rhythmic pacing, rate control, and stress manipulations on the production of longer speech units in adults with AOS is limited. That is, among the reports cited, only five subjects were studied under conditions that permit valid conclusions to be drawn regarding the relationship between application of the facilitative technique and the dependent measures reported (Southwood, 1987; Dworkin et al., 1988; Dworkin and Abkarian, 1996; Wambaugh et al., 1999). Whereas each of these studies reported positive results, it is difficult to compare them because of differences in the severity of the disorder, in the frequency, duration, and context in which the various facilitative techniques were applied, in the behaviors targeted for intervention, and in the extent to which important aspects of treatment effectiveness (i.e., generalized effects) were evaluated. As such, the limited available evidence suggests that techniques that reduce the rate of articulatory movements and highlight rhythmic and prosodic aspects of speech production may be efficacious in improving segmental coordination in longer speech units. However, until these findings can be systematically replicated, their generalizability remains unknown.

General Principles of Motor Learning

The contemporary explication of AOS as a disorder of motor planning and programming has given rise to a call for the application of motor learning principles in the treatment of AOS (McNeil et al., 1997, 2000; Ballard, 2001). The habituation, transfer, and retention of skilled movements (i.e., motor learning) and their controlling variables have been studied extensively in limb systems from the perspective of schema theory (Schmidt, 1975). This research has led to the specification of several principles regarding the structure of practice and feedback that were found to enhance retention of skilled limb movements post-treatment, and greater transfer of treatment effects to novel movements (Schmidt, 1991). Three such principles are particularly relevant to the treatment of AOS: (1) the need for intensive and repeated practice of the targeted skilled movements, (2) the order in which targeted movements are practiced, and (3) the nature and schedule of feedback.

With respect to the first of these principles, clinical management of AOS has long espoused intensive drill of targeted speech behaviors (Rosenbek, 1978; Wertz et al., 1984). However, no studies have examined the effects of manipulating the number of treatment trials on the acquisition and retention of speech targets in AOS, and little attention has been paid to the structure of drills used in treatment. That is, research on motor learning in limb systems has shown that practicing several different skilled actions in random order within training sessions facilitates greater retention and transfer of targeted actions than does blocked practice of skilled movements (Schmidt, 1991). This finding has been replicated by Knock et al. (2000) in two adult subjects with AOS in the only study to date to experimentally manipulate random versus blocked practice to examine acquisition, retention, and transfer of speech movements.

The final principle to be discussed concerns the nature and schedule of feedback employed in the training of skilled movements. Two types of feedback have been studied, knowledge of results (KR) and knowledge of performance (KP). KR provides information only with respect to whether the intended movement was performed accurately or not. KP provides information regarding aspects of the movement that deviate from the intended action and how the intended action is to be performed. Schmidt and Lee (1999) argue that KP is most beneficial during the early stages of training but that KR administered at low response frequencies promotes greater retention of skilled movements. Both types of feedback are frequently employed in the treatment of AOS. Indeed, the facilitative techniques of integral stimulation and phonetic placement provide the type of information that is consistent with the concept of KP. However, these facilitative techniques are most frequently used as antecedent conditions to enhance target performance, and response-contingent feedback frequently takes the form of KR. The effects of the nature, schedule, and timing of performance feedback have not been systematically investigated in AOS.

In summary, AOS is a treatable disorder of motor planning and programming. Studies examining the effects of facilitative techniques aimed at improving postural shaping and phasing of the articulators at the segmental level and sequencing and coordination of segments into long utterances have reported positive outcomes. These studies are in need of carefully controlled systematic replications before generalizability can be inferred. Further, the effects of motor learning principles (Schmidt and Lee, 1999) on the habituation, maintenance, and transfer of speech behaviors require systematic evaluation in persons with AOS.