Verbal Dyspraxia and Its Treatment

The verbal dyspraxic individual experiences difficulty with oral expressive production which manifests itselfin misarticulating, struggling to achieve the correct articulatory patterns and transitionalizingfrom one pattern to the next. Whether phonological selection errors occur is a controversial issue. Prosodic aspects of speech are often involved; however, whether as an integral part of the disorder itself or as a compensatory mechanism to preserve intelligibility is not entirely clear. General guidelines for treatment are outlined and are utilized in conjunction Ivith a content network to comprise a therapy program. From his established baseline performance, each client progresses through the network in a step-wise fashion with a program individually tailored to meet his needs. With improvement less stimulus and re sponse support from the clinician are required to achieve response criterion. For those who cannot achieve normal speech production, compensatory or other facilitating response variables are maintained. The speech characteristics now associated with the term verbal dyspraxia have been described in the literature for over a century. It is recognized that Broca's 1861 description of aphemia, the loss of the faculty of articulated speech, was comparable with later descriptions of verbal dyspraxia. Credit for the first detailed description and use of the term apraxia goes to Hugo Liepmann, a German neurologist (1900, cited in Trost, 1970). However, Liepmann's interests were not specifically related to verbal material as his classification of apraxias into ideational, ideo-kinetic, and limb-kinetic types reveals. The terms, apraxia or dyspraxia, have been used to refer to impairments in both speech and nonspeech motor movements, with consequent references to verbal dyspraxia, oral apraxia, and limb apraxia. When referring to speech, various other terms have been used, including apraxia of speech, cortical stuttering, and cortical dysarthria, etc. Verbal dyspraxia and apraxia of speech have had the most widespread usage in the literature and the impairment is usuaIJy defined as a motor speech programming disorder which occurs in the absence of paralysis, paresis, or disco-ordination of the neuromuscular system. Recent research findings have implicated involvement of the phonological system in the production of Broca's aphasics (Blumstein, Cooper. Zurif. and Carramaza. 1977) thereby suggesting that the view of verbal dyspraxia as simply a motor speech programming impairment is too narrow. This issue, discussed in detail below, is mentioned at this point to explain the adoption of a broader definition. Verbal dyspraxia refers to a.breakdown in the phonological-articulatory aspects of speech-language production, resulting in articulatory errors and prosodic alterations. The disturbance is due to unilateral brain damage to the dominant hemisphere and occurs in the absence of paralysis. paresis, or disco-ordination of the neuromuscular system. Verbal dyspraxia may be accompanied by oral apraxia or limb apraxia but can also occur independently (DeRenzi. Pieczuro, and Vignolo, 1966). Its occurrence as part of the symptom complex of Broca's aphasia is hotly disputed, with Darley and his co-workers (Darley, 1970; 10hns and Darley, 1970) arguing for the independence of verbal dyspraxia from aphasia while Canter and his' 'associates (Canter, 1969; Trost and Canter. 1974) and Martin (1973) and Martin and Rigrodsky (1974) argue for their association as features of Broca's aphasia. Verbal dyspraxia is a disorder that occurs int;Jotl") children and adults. In children. the disorder has been reported te 'ur in isolation or in association with language problems (Rosenbek HUMAN COMMUNICATION, SPRING, 1980 and Wertz, 1972). Generally, the diagnostic characteristics are superior rec eptive language skills compared to expressive language skills, with the latter being freque ntly difficult to evaluate due to unintelligible speech. Imitation skills are extremely poor an d articulation is characterized by inconsistent substitution and omission errors. Consonants a re more difficult to articulate correctly than are vowels and diphthongs. Phoneme productio n in isolation is better than in words and phrases. Articulatory diadochokinetic rates for singl e syllables, such as /Pd, td, b / are markedly better than those for a patterned sequence, such as ipdt;lb/, which the child may not be able to produce correctly at all. Some children dem onstrate normal prosodic aspects of speech; however, at a normal speech rate they are freque ntly unintelligible. Others modify prosodic aspects, using a slow rate and equalized stress. Yoss and Darley (1974a) suggest that the prosodic alterations are a compensatory mec hanism used to maximize intelligibility. The characteristics of verbal dyspraxia in adults have been described by ma ny authors, with the work of Darley, Canter, Blumstein, and their co-workers representing three important sources. While the studies have used different stimuli, methods of presentati on, and response scoring systems. researchers generally agree on the following characterist ics. I. Verbal dyspraxia differs from dysarthria and literal paraphasia. 2. There is a hierarchy of increasing difficulty for phonemes from vow els to singleton consonants to consonant clusters. 3. Phonemic substitutions are the most predominant error type. Substitutions are inconsistent. 4. Place of articulation is the most vulnerable feature to error. 5. The number of errors increases with increasing syllabic length of the w ord. A more detailed delineation of characteristics can be obtained by referring to the bibliographical references. Certain controversies about verbal dyspraxia can affect the treatment plan adopted by the speech-language pathologist and are therefore presented prior to the discussi on of treatment. The first controversy deals with the question of whether verbal dyspraxia is exclusively a motor problem one of sequencing the neuromotor patterns for speech. Som e advocate that sensory aspects, such as proprioception, are also involved (Hunter, 1975) . Hunter argues that, in children, abnormal proprioceptive feedback interferes with the norma l motor learning of articulatory gestures. However, she fails to provide empirical data to sup port her claim or to indicate the prevalence of proprioceptive deficits in children with ve rbal dyspraxia. Certainly. if its presence can be demonstrated, consideration should be given to it in a treatment plan. Because of her theoretical view of verbal dyspraxia as bot h a sensory and motor impairment, Hunter (1975) emphasizes oral proprioceptive and or al stereognostic experience during the early treatment phases of developmental dyspraxia. Sin ce its usefulness was based on a subjective report, empirical validation of its effectivenes s remains to be demonstrated. Treatment of verbal dyspraxia has frequently included another sensory ap proach, training auditory perception. Despite its widespread use, Yoss and Darley (1974b) reported that the approach has met with little success when used with children. In adults, Luria (1966) and Schuell et al. (1964) have described some prod uction problems with impaired proprioceptive feedback as their basis, specifically afferent kin etic aphasia and simple aphasia with persisting dysarthria. Some authors (Chappell, 1973; A ten, Johns, and Darley. 1975) also noted auditory and/or oral perceptual deficits in some dy spraxic patients. However, these impairments are not present in the majority of adults (Trost, 1970) and are not considered as an integral part of the disorder. In summary, most individuals demonstrating verbal dyspraxia do not e vidence sensory impairment. However, should sensory impairment accompany verbal dyspra xia, the speechlanguage pathologist should account for its presence in the treatment plan .