Two current classification systems focus on functional (non-organic) developmental speech disorders. Shriberg and Kwiatkowski (Shriberg and Kwiatkowski 1982, 1994 Shriberg 1993, 1994) differentiate speech disorders according to the following aetiological factors: (1) unknown origin (possibly genetic), (2) OME, (3) developmental verbal apraxia and (4) developmental psychological involvement. The other approach focuses on symptomatology (Dodd 1995, Stackhouse and Wells 1997). Underlying psycholinguistic deficits are identified in the speech processing chain by analyses of surface error patterns (number and type of speech errors). Dodd (1995) hypothesizes four different subgroups of speech disorder.
- Articulation disorder, i.e. an inability to produce a perceptually acceptable version of particular phones, either in isolation or in any phonetic context (e.g. a lateral lisp). The hypothesized deficit is at the level of phonetic planning, i.e. the sequence of oral movements for the production of a particular sound have been wrongly learned.
- Delayed phonological development, i.e. consistent error patterns occur that are inappropriate for a child’s chronological age but appropriate for a younger child. No specific deficit in the speech processing chain has been identified, and this group of children’s speech disorder may spontaneously resolve (Dodd etal. 2000). These children may represent the lower end of the normal curve for phonological acquisition.
- Deviant-consistent phonological disorder, i.e. use of consistent error patterns that are atypical of normal phonological development (e.g. deleting all syllable initial consonants). The hypothesized deficit is a cognitive linguistic one involving derivation of the phonological contrasts and constraints of the phonological system being acquired (Holm and Dodd 1999).
- Deviant-inconsistent phonological disorder, i.e. variable pronunciation of the same words or phonological features (e.g. vacuum cleaner pronounced ([drAkum kinA; fokum timA; bwDkjum kinA] The hypothesized deficit is at
the level of phonological assembly, i.e. selecting and sequencing sounds that constitute words (Bradford and Dodd 1994).
Investigation of possible causal factors associated with the four subgroups has been neglected because ‘it is rarely possible to establish one single causal factor’ (Dodd 1995: 4), and all the causal factors identified by Shriberg and Kwiatkowski (1982b) can sometimes be reported for a particular child. Nevertheless, it is possible that risk factors might differentiate the subgroups.
Most investigations of children with speech disorder have focused on English-speaking populations. No studies have yet investigated Shriberg’s (1994) aetiological classification system on children speaking a language other than English. Aetiological conditions, however, should not be country specific as long as they are culturally so highly comparable as North America and Germany. Therefore, Shriberg’s (1994) model should be applicable to German-speaking children with speech disorders. In contrast, Dodd’s (1995) model has been successfully applied to describe speech disorder in Putonghua (Zhu and Dodd 2000), Cantonese (So and Dodd 1994), Spanish (Goldstein 1996), Turkish (Topas and Konrot 1996) and German-speaking children (Fox and Dodd 2001). Results not only supported the four subgroups, but also showed similar percentages of distributions for each subgroup. These findings are of importance because they support the idea that speech disorders are a universal phenomenon and that this classification model is universally applicable. Furthermore, classification validity could demonstrated to be high (Fox and Dodd 2001). Therefore, the current study investigated German-speaking children with functional developmental speech disorders and addressed the following questions.
- Is it possible to apply successfully both classification systems independently on one group of children with developmental functional speech disorders?
- Is it possible to find a connection between underlying psycholinguistic deficits and risk factors present in the children assessed? If so, it will be hypothesized that for the group with phonological delay factors such as otitis media might be of importance (factor of developmental disturbance) and that a high incidence of affected family members (genetic origin) is likely found in children with a deviant-consistent phonological disorder.
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