3-factor causal model of moments of stuttering

3-factor causal model of moments of stuttering To make progress towards stuttering recovery, I am inviting everyone to discuss the 3-factor causal model in stuttering. The three factors are: 1. a deficit in the neural processing 2. triggers (increase the demands on the speech system) 3. modulating factors (that determine the triggering threshold) >**Triggers** > >"As discussed earlier stuttering does not occur on every syllable, so there must be a trigger for each moment of stuttering. The P&A model suggests that these triggers consist of certain inherent features of spoken language. They are more likely to trigger stuttering because they are associated with increased motor demands. These increased demands perturb the already unstable system responsible for the production of spoken language and hence trigger moments of stuttering. Of course, the idea that stuttering is associated with various linguistic features is not new. However, what is novel here is that language is not necessarily impaired in people who stutter but rather there are inherent features of language that, when realized in speech, trigger stuttering. > >The first of these proposed triggers is variable syllabic stress. This idea was integral to the development of the Variability model or Vmodel (Packman, Onslow, Richard, & van Doorn, 1996). This model was developed to explain why the novel speech pattern known as prolonged speech is so effective in reducing stuttering. This speech pattern has been used extensively and is still widely used for instating stutter free speech in behavioral treatments for older children and adults (for example, see Ingham, 1984, Langevin et al., 2006, O’Brian et al., 2003). As it has been taught, historically, the speaker slows the speech rate and prolongs sounds and words, shaping this towards natural sounding speech, which can then be used in everyday situations (see Ingham, 1984, Packman et al., 2000). However, an acoustic analysis of vowel duration indicated that using prolonged speech actually reduced variation in stress from syllable to syllable (see Packman et al., 1996). This was an unexpected finding, as clients are not taught to do this when learning prolonged speech. The Vmodel, then, explains the reductions in stuttering that occur with prolonged speech as due to reduction in the variability in contrastive syllabic stress. Reduction in the variability of syllabic stress is also a feature of syllable-timed or rhythmic speech, which is an even more powerful stuttering suppressant, or fluency enhancing condition (see Ingham, 1984, Packman et al., 2000). Reducing the variability in emphasis from syllable to syllable in both these speech patterns simplifies speech production considerably and so reduces the motoric task demands on an unstable speech production system. > >The second trigger identified in the P&A model is linguistic complexity. Linguistic complexity has been an area of interest in the study of stuttering for decades, with research findings suggesting that stuttering tends to occur in utterances that are linguistically more complex (Bloodstein & Bernstein Ratner, 2008). The P&A model attributes this to the motoric task demands that this complexity places on the unstable speech system. Linguistic complexity renders speech movements unstable (Kleinow & Smith, 2000) and these authors concluded with the hypothesis that, “linguistic complexity is one factor that contributes to the disruptions of speech motor stability characteristic of stuttering” (Kleinow & Smith, 2000, p. 548). In the P&A model, then, linguistic complexity, like varying syllabic stress, is an inherent feature of normal spoken language that triggers stuttering in speakers whose neural processing for speech is compromised by inefficient transmission in the connective white fibers. > >The question arises, then, whether there is a relationship between the production of variable linguistic stress and linguistic complexity. It may be that increased linguistic complexity may involve increased variability in contrastive syllabic stress. This is an empirical question waiting to be answered. > >**Modulating factors** > >In the P&A model, the triggering mechanism is modulated by intrinsic factors. The main one is physiological arousal. According to the P&A model, the level of physiological arousal in an individual can alter the threshold at which a moment of stuttering is triggered. Here, physiological arousal refers to the readiness of the body to react to stressful internal and external stimuli. For example, a competitive tennis player may do a perfect backhand shot in practice but mistime it when in competition. Or a violinist may play Bach wonderfully in rehearsal but make errors when performing in public. These two examples relate to performance anxiety, but arousal can increase with excitement or anticipation or fear. Similarly, there is considerable evidence that stuttering severity can vary according to communicative context (Ingham, 1984). However, there is unlikely to be a straightforward linear relationship between arousal and stuttering severity, within individuals. For example, if a person uses a fluency enhancing technique, such as prolonged speech, an increase in arousal may result in them paying more attention to it, hence increasing their control over their stuttering. This is another empirical question raised by this model. > >The availability of cognitive resources during communication has also been shown to have an effect on stuttering (see Metten et al., 2011). Metten et al. (2011) found that stuttering increased when a competing linguistic task diverted cognitive resources away from speaking. Interestingly, dual tasking also interfered with speech production for the normally fluent participants in the control group, who had many more normal disfluencies in this condition. According to the P&A model, then, dual- or multi-tasking where the tasks share resources can lower the threshold at which stuttering is triggered. Interestingly, it is also the case that stuttering may reduce during dual tasking where the secondary task does not share cognitive resources (Arends et al., 1988, Vasic and Winjen, 2005). > >In this model, the modulating factors are considered to be unique for each individual. For example, in a study of 140 adults seeking treatment for their stuttering, Iverach et al. (2011) found wide variation in scores on the Unhelpful Thoughts and Beliefs About Stuttering scale and on a range of psychological tests. Modulating factors will likely be influenced by, among other things, individual experiences (for example, teasing during childhood), anxiety, fear of negative evaluation and stuttering severity, all in turn possibly influenced by individual differences in emotional reactivity (Walden et al., 2012) and resilience (Craig, Blumgart, & Tran, 2011). > >Environmental stressors are seen as important in the P&A model, just as they are in the Demands and Capacities model. However, in the P&A model the individual's perceptions of, and/or reactions to, potential environmental stressors are also important in determining the threshold at which stuttering is triggered. For example, one person who stutters may be highly anxious when talking in a group, whereas another may not. Modulating factors, then, can be seen as the major contributor to the variability of stuttering within individuals, across communicative contexts. > >To summarize the P&A model, an underlying deficit in neural processing is the necessary condition for stuttering to occur, while features of spoken language trigger moments of stuttering. Together, these form the necessary and sufficient conditions for a moment of stuttering to occur. In the model, differences in stuttering severity across individuals can be attributed to differences in the extent of the neural processing deficit across individuals, while variability of stuttering within individuals, across communication contexts, can be attributed to the range and potency of modulating factors in individuals."