Fluency is the aspect of speech production that refers to continuity, smoothness, rate, and effort. Stuttering, the most common fluency disorder, is an interruption in the flow of speaking characterized by repetitions (sounds, syllables, words, phrases), sound prolongations, blocks, interjections, and revisions, which may affect the rate and rhythm of speech. These disfluencies may be accompanied by physical tension, negative reactions, secondary behaviors, and avoidance of sounds, words, or speaking situations (ASHA, 1993; Yaruss, 1998; Yaruss, 2004). Cluttering, another fluency disorder, is characterized by a perceived rapid and/or irregular speech rate, which results in breakdowns in speech clarity and/or fluency (St. Louis & Schulte, 2011).
Stuttering can greatly interfere with school, work, or social interactions (Yaruss & Quesal, 2004). Children who stutter may report fear or anxiety about speaking and frustration or embarrassment with the time and effort required to speak (Ezrati-Vinacour, Platzky, & Yairi, 2001). Children who stutter may also be at risk for experiencing bullying (Blood & Blood, 2004; Davis, Howell, & Cooke, 2002; Langevin, Bortnick, Hammer, & Wiebe, 1998). Stuttering can co-occur with other disorders, such as speech sound disorders (St. Louis & Hinzman, 1988; Wolk, Edwards, & Conture, 1993); intellectual disabilities (Healey, Reid, & Donaher, 2005); and language disorders (Ntourou, Conture, & Lipsey, 2011). For example, although there is little systematic evidence describing disfluency in autism spectrum disorder (ASD), increasing numbers of case reports indicate both stuttering-like disfluency and non-stuttered (typical) disfluency (Scaler Scott, Tetnowski, Flaitz, & Yaruss, 2014) and atypical disfluency that is additionally distinguished by unusual features, such as repetition of final segments of words (Paul et al., 2005; Shriberg et al., 2001; Sisskin & Wasilus, 2014).