Differentiating Speech Delay from Disorder Does It Matter?

Top Lang Disorders Vol. 31, No. 2, pp. 96–111 Copyright c 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Differentiating Speech Delay From Disorder Does it Matter? Barbara Dodd Aim: The cognitive-linguistic abilities of 2 subgroups of children with speech impairment were compared to better understand underlying deficits that might influence effective intervention. Methods: Two groups of 23 children, aged 3;3 to 5;6, performed executive function tasks assessing cognitive flexibility and nonverbal rule abstraction. Following the system of differential diagnosis of speech disorders first described by Dodd, Leahy, and Hambly (1989), one group was identified as having delayed speech development, as their non–age-appropriate speech error patterns were typical of younger children. The other group was diagnosed as disordered because children consistently used at least one speech error pattern atypical of any age group in an assessments’ normative sample (Dodd, Zhu, Crosbie, Holm, & Ozanne, 2002). Results and Conclusions: The disordered group performed less well than the delayed group: They had poorer cognitive flexibility and difficulty abstracting nonlinguistic rules. They made more consonant errors and different types of errors. The 2 groups did not differ on measures of language, vowel accuracy, or consistency of multiple productions of the same words. The findings suggest that different interventions, reflecting knowledge of underlying deficits, might benefit specific subgroups of children with speech impairment. Key words: cognitive flexibility, error patterns, executive functions, speech delay, speech disorder LL YOUNG CHILDREN make errors 5 years. Researchers have argued that error A when pronouncing words (e.g., [pun] pattern change indicates linguistic reorgani- spoon; [tæt] cat). Most children of a partic- zation of the phonological system that occurs ular age share the same error patterns, with in a systematic order, within specific time different error patterns characterizing spe- frames and without explicit instruction (Grun- cific age bands. In English, for example, stop well, 1977; Macken, 1979; Williams, 1993). may initially be pronounced as [tɒ], followed Reorganization reflects cognitive-linguistic de- by [tɒp], then correctly as [stɒp]. English- velopment that allows children to identify speaking children’s speech comes to resem- the phones, contrasts, and phonotactic con- ble the adult-target production by around straints of the language being learned. Although most children exposed to the same language use error patterns that resolve Author Affiliation: Department of Language and at somewhat similar ages (Grunwell, 1997; Communication Sciences, City University, London, United Kingdom. Preisser, Hodson, & Paden, 1988), this is not The study reported was funded by the Australian Re- the case for all children. The most common search Council Discovery Grants Scheme. diagnosis made by clinicians working with The willing cooperation of childcare centers, parents, pediatric caseloads is speech impairment.1 and children is gratefully acknowledged. The author Children’s errors make their speech difficult thanks Beth McIntosh, Sharon Crosbie, Aileen Wright, and Alison Holm for practical help and discussion. Corresponding Author: Barbara Dodd, PhD, De- partment of Language and Communication Sciences, City University London, Northampton Square, London 1The term “speech impairment” is used rather than the EC1V OHB, United Kingdom (e-mail: Barbara.Dodd.1@ current generic term “speech sound disorder,” which city.ac.uk). denotes all speech difficulties including both delay and DOI: 10.1097/TLD.0b013e318217b66a disorder. 96 Differentiating Speech Delay From Disorder 97 to understand resulting in communication role of cognitive-linguistic abilities for typi- breakdowns that place them at risk for so- cal phonological development followed by a cial and academic, particularly literacy, fail- summary of findings from research compar- ure (Gillon, 2004). The National Institute on ing children with delayed as opposed to dis- Deafness and Other Communication Disor- ordered speech impairment. Delayed speech ders (1994) estimated that 10% of children development is defined by the presence of receive intervention for impaired speech in- speech error patterns, each observed in at telligibility in the United States. An incidence least five different lexical items in a 50-word survey of a speech-language pathology service picture-naming task, that are typical of at least in England (Broomfield & Dodd, 2004a), re- 10% of children of a younger chronological ported that 6.4% of all children are treated for age in the normative data for that standard- speech impairment. ized assessment. To be classified as having Successful intervention for speech impair- disordered speech, children must evidence at ment relies on clinicians’ knowledge of least one speech error pattern, identified as the nature of the deficit underlying chil- occurring at least five times in different lexi- dren’s impairment (Stackhouse & Wells, cal items in the 50-word task, that is atypical of 1997). Although some children with speech any age group in the normative sample for the impairment have been shown to have assessment. deficits in input (e.g., Boets, Ghesquiere, van Wieringen, & Wouters, 2007) or output (e.g., motor processing, Gibbon, 1999), many re- Typical speech development searchers have argued that most children’s Three primary factors are posited as alter- speech impairment reflects a linguistic (i.e., native explanations for developmental errors phonological) impairment (Bowen, 2010; in speech during the acquisition of phonol- Gierut, 1998; Stackhouse & Wells, 1997; Vih- ogy: output, input, and cognitive linguistic man, 1996). This hypothesis was examined by processing. a study comparing the auditory-visual speech 1. Output approaches: Motor theory holds perception, oral-motor ability, and cognitive- that children gradually master the intri- linguistic processing skills of 78 children with cacies of sequencing complex articula- speech impairment (mixed delay and disor- tory movement that reflects more gen- der) and 87 age-matched controls aged 3 to 6 eral motor maturity (e.g., Green, Moore, years (Dodd & McIntosh, 2008). No child in & Reilly, 2002). For example, McCune the group with speech impairment was identi- and Vihman (2001) argued that children fied as having an input difficulty, and only two establish “vocal motor schemes” for con- children performed below the normal range sonant production that influence the er- on an oral sequenced-movements task. In con- ror types made in early phonological de- trast, the group with speech impairment per- velopment. formed significantly less well than controls on 2. Input approaches: Immature input pro- both cognitive-linguistic tasks of rule abstrac- cessing has been claimed to explain de- tion and cognitive flexibility. velopmental errors. Some researchers ar- This article examines the processes2 of cog- gue that, as children’s ability to discrim- nitive flexibility and rule abstraction in chil- inate differences between the speech dren with speech impairment. The literature sounds of their native language gradually review first highlights the importance of the improves, it allows more accurate production (e.g., Edwards, Fox, & Rogers, 2002). Discrimination tasks might, however, evaluate phonological learn- 2The term “processes” refers in this article to the cogni- ing rather than auditory-visual speech tive abilities underlying phonological development. perception. For example, Burnham, 98 TOPICS IN LANGUAGE DISORDERS/APRIL–JUNE 2011 Earnshaw, and Clark (1991) showed that Speech impairment the development of the ability to discrim- Children with speech difficulties are het- inatespeechsoundsis“tuned”postin- erogeneous, differing in severity, underlying fancy. The infant ability to discriminate cause, speech error characteristics, profile of contrasts not relevant to their native lan- associated abilities and response to treatment. guage (Jusczyk, 1992) is lost so that chil- In Broomfield and Dodd’s (2004b) incidence dren older than 2 years are unable to study, 320 children with speech difficulties discriminate between similar sounds that were assessed. Of this group, 12.5% had an ar- are not native language phonemes. ticulation disorder, which was defined as an 3. Cognitive-linguistic processing appro- inability to produce a perceptually acceptable aches: Cognitive-linguistic approaches version of phones due either to a physiolog- propose that children’s ability to process ical condition such as dysarthria or mislearn- speech changes over time, reflecting the ing of the sounds’ motor program (e.g., lisp). development of other general mental Most of the children assessed (57.5%) had a abilities such as phonological working phonological delay characterized by all errors memory (Adams & Gathercole, 2000), being accounted for by phonological error processes for forming and revising lexi- patterns (e.g., cluster reduction and fronting) cal representations (Elbro, 1993), and/or that occur during typical speech development cognitive capacities for rule abstraction at a younger chronological age level. Chil- (Dodd & Gillon, 1997). dren who used one or more error patterns We studied the contribution of input, that were atypical of normal development output, and cognitive-linguistic abilities to in English (e.g., backing, favored sound, and phonological development in one group of 2- initial consonant deletion) were classified as year-old children

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