The EXPLAN theory of fluency control applied to the diagnosis of stuttering

In the following two chapters, we present an overview of the EXPLAN theory. The main focus of EXPLAN is on fluent speech control (Howell & Au-Yeung submitted; Howell, Rosen, Hannigan & Rustin 2000; Howell & Sackin 2000, submitted) but it is also relevant to diagnosis (Au-Yeung, Howell & Pilgrim 1998; Howell, Au-Yeung, Davis, Charles, Sackin, Williams, Cook, Rustin & Reed in press; Howell, Au-Yeung & Sackin 1999) and treatment of stuttering (Howell, Au-Yeung & Vallejo-Gomez in press; Howell & Sackin in press). Fluency failures (Howell & Au-Yeung submitted) can affect normally fluent as well as stuttered speech. Fluency failure occurs where speech control falters even though the speaker does not produce an overt error. An extract including several types of fluency failure (detailed later) is “I got on, on the seven ... fffifty ... three train t.to Mac... clesfield.” According to EXPLAN, all fluency failures arise from the same generic problem. This problem leads to specific types of fluency failure that are shown by all children. The difference between fluency failures in child and adult stuttering is due to a change in the way the underlying problem is dealt with by people who stutter. This change leads to fluency failures with different characteristic surface (speech output) forms. As all speakers experience the same generic problem, they all could, in principle, tackle the problem in the same way as adults who stutter. According to EXPLAN, the distinguishing characteristics of stuttering emerge in late childhood; a contrasting view is that people who stutter have incipiently different problems in controlling speech from the onset of language. Viewed from the EXPLAN perspective, then, diagnosis of the disorder involves specifying and measuring the types of fluency failures that occur in late adolescence to see if they have changed in the way commensurate with adult stuttering. EXPLAN supports the view that young speakers whom clinicians suspect might develop the disorder need to be monitored. However, the theory suggests that early intervention may not be advisable in such suspected cases (not as long as the child is exhibiting the types of fluency failure common to all children). We will begin by examining how fluency control has been explained in a representative psycholinguistic model (Levelt 1989) that contrasts in many respects with EXPLAN. Levelt’s model was selected for this comparison because it attempts to explain all events between intention and action in language. The points made about Levelt’s (1989) model also apply to more recent versions by the same author (e.g. Levelt, Roelofs & Meyer 1999). A final reason for choosing Levelt’s (1989) model is that it has also been the basis of a model of adult stuttering (the Covert Repair Hypothesis, CRH, Kolk & Postma 1997).