Apraxia

The diagnostic criteria used to identify developmental apraxia of speech (DAS) have been at the center of controversy for decades. Despite the difficulty in determining the characteristics that differentiate DAS from other speech acquisition disorders, many children are identified with this disorder. The current report presents the criteria used by 75 speech-language pathologists to establish a diagnosis of DAS. Although 50 different characteristics were identified, 6 of these characteristics accounted for 51.5% of the responses. These characteristics included inconsistent productions, general oral-motor difficulties, groping, inability to imitate sounds, increasing difficulty with increased utterance length, and poor sequencing of sounds. These results are consistent with the general ambiguity of the diagnostic criteria of DAS and suggest that no single deficit is used among clinicians.

Key Words: developmental apraxia, children, speech, diagnosis

Developmental apraxia of speech (DAS) has been labeled as a disorder "in search of a population" (Guyette & Diedrich, 1981, p. 39) largely because of the ambiguity surrounding the nosological criteria used to establish a diagnosis. The existence of DAS as a distinct disorder continues to be debated, with some reports suggesting that the disorder is subsumed under the general category of phonological disorder (Gierut, 1998), whereas other classification schemes regard DAS as a separate disorder with a motor-based etiology (Robin, 1992). Despite this controversy, the label of DAS continues to be assigned to some children with speech sound acquisition problems.

Of late, research has been reassessed in an effort to differentially define DAS (Davis, Jakielski, & Marquardt, 1998; Shriberg, Aram, & Kwiatkowski, 1997a, 1997b, 1997c; Stackhouse, 1992); unfortunately, these analyses do not result in a singular perspective on the disorder. For example, Shriberg et al. (1997e) concluded that inappropriate stress production serves to differentiate children with DAS from those with speech delays of unknown etiology. Prospective investigations to evaluate this proposal have yielded varied results (Munson et al., 2003; Skinder, Strand, & Mignerey, 1999; Velleman & Shriberg, 1999). Skinder et al. found that when listeners were asked to evaluate stress production by children with DAS and their normally articulating peers, children with DAS were perceived to be less accurate than children with normal articulation. However, acoustic analyses did not identify the basis for this percept. Similar results were found when comparisons were made between children diagnosed with DAS and those identified as having a phonological disorder; that is, although listeners judged differences in stress production, no significant acoustic differences were found in the control of prosody (Munson et al., 2003). Results presented by Velleman and Shriberg yielded an intermediate proposal. In this study, metrical phonology was applied to the data presented by Shriberg et al. (1997b, 199Tc) to determine if lexical stress patterns differed for children with suspected DAS and those children with speech delays of unknown origin. In general, patterns of lexical stress errors were consistent across these groups of children and were comparable to previous investigations of lexical stress production in typically developing children. One difference that did emerge from this metrical analysis was that children with suspected DAS who were perceived to produce inappropriate sentential stress maintained patterns of syllable omission to a later age than was found in the children with speech delay. In summary, perceptual analyses of stress generally point to a deficit in children with DAS; the basis of this deficit is unclear in that both acoustic and metrical phonological analyses do not explain these perceptual effects.

Stackhouse (1992) proposed four independent factors to characterize DAS. In addition to phonetic deficits, Stackhouse suggested that a child must demonstrate motor, cognitive, and linguistic disturbances to be diagnosed with DAS. Although experimental evaluation of this proposal has been limited to two case studies (Stackhouse & Snowling, 1992), Ozanne's (1995) retrospective analysis of children's speech errors provides a similar perspective. By contrast, Davis et al. (1998) identified only speech production errors, including some problems that are typical in most children with speech delays (e.g., limited phonetic inventory) as well as some atypical features (e.g., high variability, vowel errors, and suprasegmental deficits) in children with DAS.

Other investigations have centered on identifying the diagnostic criteria for DAS relative to age-appropriate speech acquisition (Thoonen, Maassen, Gabreels, Schreuder, & de Swart, 1997) and have identified singleton consonant errors and cluster reduction as distinguishing factors. These criteria may not serve to distinguish children with DAS from children with phonologically based disorders (Forrest & Morrisette, 1999).

Given the ambiguity of the defining characteristics of the disorder, it is not surprising that the prevalence of DAS is unknown (American Speech-Language-Hearing Association, 2002). However, the numerous Web sites, therapy materials, and discussions on the topic would suggest that the disorder is not uncommon. As many reviews indicate (Davis et al., 1998; McCabe, Rosenthal, & McLeod, 1998; Ozanne, 1995) there are many different factors that have been identified to distinguish DAS and often there are contradictory perspectives regarding the signs and symptoms of the DAS. For example, difficulties with nonspeech movements have been cited to characterize DAS in some reports (e.g., Hall, 2000), whereas others have not specified any causal relationship between DAS and other oral-motor behaviors (e.g., Davis et al., 1998; Shriberg et al., 1997a, 1997b, 1997e).

It is clear that considerable effort is being made to develop the nosological criteria for DAS; however, controversy surrounding the criteria for diagnosis still remains. Despite the lack of such a definition, children are being diagnosed with this disorder. If children receive a clinical diagnosis of DAS, what are the deficits that lead to this assessment? In the present article, this issue was addressed by asking a sample of speech-language pathologists (SLPs) to indicate the criteria that they use to establish a diagnosis of DAS.

Method

Participants

Participants included 75 SLPs who attended a continuing education workshop sponsored by the Indiana Speech-Language-Hearing Association in February 2000. The topic of the 1-day workshop, presented by the author, was assessment and treatment of DAS. Although no precise demographics were obtained from the participants, information about the workshop indicated that it was geared toward SLPs working with preschool and schoolage children. According to the Continuing Education Coordinator for the state organization, more than 90% of the people who attended this workshop were employed as SLPs and held the required state licensure for their work environment (A. Densmore, personal communication, May 2002). An informal survey of the participants revealed that about 40% of the participants worked in home-based early intervention settings, 50% of the workshop attendees worked in the public schools, and the remainder of the SLPs in the audience worked in hospitals or university clinics. Most of the participants indicated that they worked with children who were diagnosed with DAS. This information was obtained by a "show of hands" when participants were asked if they had children with DAS in their caseloads. No information was obtained about the amount of experience that these clinicians had with children with speech sound disorders of any etiology. Visual examination of the audience indicated that the majority of participants were women, with approximately 5 men in attendance.

Procedures

At the start of the workshop, following the introductions, the workshop participants were asked to write down three characteristics that they felt were necessary to result in a diagnosis of DAS. The purpose of this request was to obtain information for discussion within the workshop and to give participants a sense of the potential diversity associated with the term. Participants were given 10 min to complete their responses and responses were collected. Questions that arose, mostly relating to the necessity to list three criteria, were answered but no additional instructions were provided. In response to the question about the requirement to include three criteria, the instructions were altered to require up to three features of DAS. Therefore, all responses can be considered to emerge from an open-ended set; however, because of the limitations placed by the instructions (i.e., list up to three features) the responses may not represent all the characteristics that a given clinician uses to diagnose DAS.

The author tabulated the responses during the lunch break and the results were relayed to the participants at the start of the afternoon session. More careful examination of the data was undertaken at a later date to determine frequency counts for all characteristics that were mentioned by the participants. When possible, features were grouped to reflect similarities between responses. Many of the categories were identical to participants' responses (e.g., motor programming problem). Decisions about group affiliation for the remaining responses were based on thematic similarities and inductive analysis. For example, responses that referred to increased number of errors with increased syllables or words were grouped in the category increased errors with increased utterance length; the category inconsistent production comprised responses that indicated problems in repeated productions of the same word or sound as well as responses that noted inconsistency within a sound across contexts. In many cases, the correspondence between different participants' responses was not clear, so these features were listed separately (e.g., swallowing problems, regression of word production).

Because the participants were not asked to rank order the criteria, all characteristics were given equal weight.

Results

Of the 75 participants in this workshop, 67 provided three criteria that would lead to a diagnosis of DAS; the remaining 8 participants listed only two criteria for this disorder. Responses from participants indicated 50 different characteristics that were used to diagnose DAS. Table 1 lists the criteria that were suggested as well as the frequency with which that characteristic was noted. The criteria that were noted most frequently include inconsistent productions, groping/effortful productions, general oral-motor difficulties, inability to imitate sounds, increasing difficulty with sound production as the utterance length increased, and poor sequencing of sounds. These six criteria accounted for 117 of the 227 responses (51.5%) that were obtained. Each of the remaining criteria was noted in less than 10 of the responses received.

Discussion

The purpose of the current research was to determine the diagnostic criteria that practicing SLPs use in identifying DAS. The results revealed that the nosological criteria for DAS remain ambiguous, as noted by the numerous characteristics that practicing SLPs used to diagnose the disorder. Clinicians' views of characteristics of DAS appear consistent with the research literature in this regard; that is, there is no standard for the definition of the term. Further, the present study is consistent with the findings of Davis et al. (1998) in that there appears to be large variation in the use of the term DAS. Whether this variability can be related to varied educational backgrounds (i.e., definitions that were learned in different educational programs), from reading of current literature, or from clinical experience, there is little congruence across SLPs in the characteristics that they use to diagnose DAS.

It is clear that many of the respondents in the current investigation use inconsistent production as a feature of DAS, yet the meaning of the term may vary. For example, some respondents indicated that DAS was characterized by inconsistent productions across repetitions of the same sound sequence or word. Other clinicians noted inconsistency in the production of a single sound across varying contexts, whereas other SLPs considered a child's production to be inconsistent if a sound was produced differently in isolation versus in conversational speech. Despite these variants of definition, inconsistency appears to be a characteristic that commonly is associated with DAS. However, even this feature was not listed by a majority of the respondents.

The utility of inconsistency as a marker for DAS is somewhat congruent with research on this disorder (Davis et al., 1998; McCabe et al., 1998; Ozanne, 1995) as well as studies that note different profiles of children with functional articulation disorders. Specifically, Forrest and her colleagues (Forrest & Elbert, 2001; Forrest, Dinnsen, & Elbert, 1997; Forrest, Elbert, & Dinnsen, 2000) found that children with variable substitutes for sounds that were excluded from the inventory had different patterns of phonological learning as a result of treatment compared to children who used a consistent substitute for an omitted sound. Children who used variable substitutes did not learn treatment targets nor show any generalization of knowledge to untreated sounds even though the techniques used had been proven effective with children with more consistent phonological error patterns (Elbert, Dinnsen, & Powell, 1984; Gierut, 1985). Although it is not clear that these children have DAS, their substitution and learning patterns suggest that they are distinct from children with more consistent sound usage. Further, Davis et al. (1998) identified these patterns as markers of DAS.

Inconsistency in speech production also has been cited as a hallmark feature of DAS by Dodd and her associates (Dodd & McCormack, 1995; Dodd & Iacono, 1989). Children with this diagnosis were found to have inconsistent phonological errors and demonstrated the use of deviant phonological processes (i.e., processes that are not seen in the typical acquisition of phonology). Further, these children showed deficits in language performance as well as motor planning of speech and nonspeech activities.

The presence of groping behavior and general oral-motor difficulties also were frequently associated with DAS. Again, this characteristic has been cited frequently in the literature (e.g., Crary, 1984, 1993; Hall, Jordan, & Robin, 1993; Ozanne, 1995; Stackhouse & Snowling, 1992). Ozanne (1995) noted groping and oral-motor problems in children with developmental verbal dyspraxia and concluded that clusters of symptoms are needed for accurate diagnosis of the disorder. She suggests that these clusters represent deficits in phonological planning, phonetic programming, and general oromotor control. The current investigation cannot confirm or refute this hypothesis, in part because of the methodology employed. That is, participants in this investigation were asked to supply "up to three" criteria that they use to diagnose DAS. It is possible that in an attempt to comply with the instructions, some participants included additional characteristics that they don't normally associate with this disorder. Other participants may have limited their responses to include only three features even though additional characteristics typically are used in their diagnosis of DAS.

Despite restrictions placed on the number of DAS features that participants should list, the results from the current investigation provide some insight into the concept of DAS. Review of Table 1 indicates that across clinicians there is great divergence in the characteristics of DAS, as noted by the 50 different features that the SLPs cited. Not only were there a large number of different features suggested as diagnostic of the disorder, but some of the criteria were contradictory. For example, some respondents viewed difficulty in speech without concomitant problems in movement of the articulators for nonspeech activities as a marker of DAS (e.g., motor problems for speech with normal movement for feeding, difficulty in voluntary speech movement), whereas other SLPs noted that general oral-motor deficits served as an important characteristic of DAS. Similarly, respondents stated that normal auditory perception should be evident in children with DAS and other clinicians indicated that auditory perception and processing impairments were markers of the disorder. This variation across individuals in the understanding of DAS may lead to errors in the diagnosis of the disorder, as noted by Davis et al. (1998). Experience in our university clinic is consistent with this claim. In our ongoing research, we have found that many children referred for evaluation and treatment of DAS show signs of dysarthria. For example, in a recent group of 10 children who had received diagnoses of DAS from area SLPs, 2 children had abnormally high velar air flow and 2 other children demonstrated excessive laryngeal resistance. These physical deviations may account for much of the treatment failure that was noted by the referring clinician.

Clearly, additional research on DAS criteria is needed. The present study is limited in that the instructions to the participants (i.e., provide three criteria for diagnosing DAS) may have forced the clinicians to provide extraneous features. Therefore, a replication of this study with less restrictive directions is warranted. Further, the participants' level of experience in working with children with articulation disorders is unknown. Although most people who attended this workshop were working as SLPs, and presumably these individuals were interested in the topic of DAS, precise information about the participants was not obtained. Finally, the participants in this study were obtained from a sample of convenience rather than by more controlled procedures. Therefore, the results of this study remain purely descriptive. Despite these limitations, the present investigation provides insight into the features that SLPs use to diagnose DAS. Although a large number of features emerged from this analysis, the category of "inconsistent errors" was most frequently cited as a diagnostic marker for DAS. However, it does not appear that there is good consensus among working clinicians regarding the characteristics that define DAS.

Acknowledgments

This research was supported by National Institute on Communication Disorders Grant DC04575.

References

American Speech-Language-Hearing Association. (2002). Retrieved July 30, 2003, from http://professional.asha.org/resources/factsheets/stroke.cfm

Crary, M. A. (1984). A neurolinguistic perspective on developmental verbal dyspraxia. Communicative Disorders, 9, 33-49.

Crary, M. A. (1993). Developmental motor speech disorders. San Diego, CA: Singular.

Davis, B. L., Jakielski, K. J., & Marquardt, T. P. (1998). Developmental apraxia of speech: Determiners of differential diagnosis. Clinical Linguistics and Phonetics, 12, 25-45.

Dodd, B., & Iacono, T. (1989). Phonological disorders in children: Changes in phonological process use during treatment. British Journal of Disorders of Communication, 24, 333-352.

Dodd, B., & McCormack, P. (1995). A model of speech processing for differential diagnosis of phonological disorders. In B. Dodd (Ed.), Differential diagnosis of children with speech disorders (pp. 65-89). London: Whurr.

Elbert, M., Dinnsen, D. A., & Powell, T. W. (1984). On the prediction of phonologie generalization learning patterns. Journal of Speech and Hearing Disorders, 49, 309-317.

Forrest, K., & Elbert, M. (2001). Treatment for phonologically disordered children with variable substitution patterns. Clinical Linguistics and Phonetics, 15, 41-45.

Forrest, K., & Morrisette, M. (1999). Feature analysis of phonemic errors in children with phonological disorders. Journal of Speech, Language, and Hearing Research, 42, 187-194.

Forrest, K., Dinnsen, D. A., & Elbert, M. (1997). The impact of substitution patterns on phonological learning by misarticulating children. Clinical Linguistics and Phonetics, 11, 63-76.

Forrest, K., Elbert, M., & Dinnsen, D. A. (2000). The effect of substitution patterns on phonological treatment outcomes. Clinical Linguistics and Phonetics, 14, 519-531.

Gierut, J. A. (1985). On the relationship between phonological knowledge and generalization learning in misarticidating children. Bloomington: Indiana University Linguistics Club.

Gierut, J. A. (1998). Treatment efficacy: Functional phonological disorders in children. Journal of Speech, Language, and Hearing Research, 41, S85-S100.

Guyette, T. W., & Diedrich, W. M. (1981). A critical review of developmental apraxia of speech. In N. Lass (Ed), Speech and language: Advances in basic research and practice (Vol. 5, pp. 1-49). New York: Academic Press.

Hall, P. K. (2000). A letter to the parent(s) of a child with developmental apraxia of speech. Part III: Other problems often associated with the disorder. Language, Speech, and Hearing Services in the Schools, 31, 176-178.

Hall, P. K., Jordan, L. S., & Robin, D. A. (1993). Developmental apraxia of speech: Theory and clinical practice. Austin, TX: Pro-Ed.

McCabe, P., Rosenthal, J. B., & McLeod, S. (1998). Features of developmental dyspraxia in the general speech impaired population? Clinical Linguistics and Phonetics, 12, 105-126.

Munson, B., Bjorum, E. M., & Windsor, J. (2003). Acoustic and perceptual correlates of stress in nonwords produced by children with suspected developmental apraxia of speech and children with phonological disorder. Journal of Speech, Language, and Hearing Research, 46, 189-202.

Ozanne, A. (1995). The search for developmental verbal dyspraxia. In B. Dodd (Ed.), Differential diagnosis of children with speech disorders (pp. 91-109). London: Whurr.

Robin, D. A. (1992). Developmental apraxia of speech: just another motor problem. American Journal of Speech-Language Pathology, 1, 19-22.

Shriberg, L. D., Aram, D. M., & Kwiatkowski, J. (I997a). Developmental apraxia of speech: I. Descriptive and theoretical perspectives. Journal of Speech, Language, and Hearing Research, 40, 273-286.

Shriberg, L., Aram, D., & Kwiatkowski, J. (I997b). Developmental apraxia of speech: II. Toward a diagnostic marker. Journal of Speech, Language, and Hearing Research, 40, 286-312.

Shriberg, L., Aram, D., & Kwiatkowski, J. (1997c). Developmental apraxia of speech: III. A subtype marked by inappropriate stress. Journal of Speech, Language, and Hearing Research, 40, 313-337.

Skinder, A., Strand, E. A., & Mignerey, M. (1999). Perceptual and acoustic analysis of lexical and sentential stress in children with developmental apraxia of speech. Journal of Medical Speech-Language Pathology, 7, 133-144.

Stackhouse, J. (1992). Developmental verbal dyspraxia I: A review and critique. European Journal of Disorders of Communication, 27, 19-34.

Stackhouse, J., & Snowling, M. (1992). Developmental verbal dyspraxia II: A developmental perspective on two case studies. European Journal of Disorders of Communication, 27, 35-54.

Thoonen, G., Maassen, B., Gabreels, F., Schreuder, R., & de Swart, B. (1997). Towards a standardised assessment procedure for developmental apraxia of speech. European Journal of Disorders of Communication, 32, 37-60.

Velleman, S. L., & Shriberg, L. D. (1999). Metrical analysis of the speech of children with developmental apraxia of speech. Journal of Speech, Language, and Hearing Research, 42, 1444-1460.

Received December 10, 2001

Accepted February 19, 2003

DOI: 10.1044/1058-0360(2003/083)

Karen Forrest

Indiana University, Bloomington

Contact author: Karen Forrest, PhD, Department of Speech and Hearing Sciences, Indiana University, 200 South Jordan Avenue, Bloomington, IN 47401.

E-mail: kforrest@indiana.edu

Copyright American Speech-Language-Hearing Association Aug 2003
Provided by ProQuest Information and Learning Company. All rights Reserved