Influences of Length and Syntactic Complexity on the Speech Motor Stability of the Fluent Speech of Adults Who Stutter

Abstract

The purpose of the present study was to investigate the impact of utterance length and syntactic complexity on the speech motor stability of adults who stutter. Lower lip movement was recorded from 8 adults who stutter and 8 normally fluent controls. They produced a target phrase in isolation (baseline condition) and the same phrase embedded in utterances of increased length and/or increased syntactic complexity. The spatiotemporal index (STI) was used to quantify the stability of lower lip movements across multiple repetitions of the target phrase. Results indicated: (a) Adults who stutter demonstrated higher overall STI values than normally fluent adults across all experimental conditions, indicating decreased speech motor stability; (b) the speech motor stability of normally fluent adults was not affected by increasing syntactic complexity, but the speech motor stability of adults who stutter decreased when the stimuli were more complex; (c) increasing the length of the target utterance (without increasing syntactic complexity) did not affect the speech motor stability of either speaker group. These results indicate that language formulation processes may affect speech production processes and that the speech motor systems of adults who stutter may be especially susceptible to the linguistic demands required to produce a more complex utterance. The present findings, therefore, support the hypothesis that linguistic complexity is one factor that contributes to the disruptions of speech motor stability characteristic of stuttering.

Persistent developmental stuttering as a cortical-subcortical dysfunction: evidence from muscle activation

“…Regarding speech RT, the data of this study agrees with the findings of Bosshardt et al 13 who found no differences between suttering and fluent individuals and with the data of Kleinow and Smith 14 who found a greater variability in the temporal patterns of stuttering individuals (in the present study the group of stutterers presented results four times more disperse than their controls). This variability, indicated by the dispersion of the data, suggests that the speech system of stuttering individuals requires several attempts prior to speech in order to reach a fluent pattern.…”

“…Several authors point that high muscle activity makes speech more vulnerable to disruptions 1,3,6,14,15 .…”

“…This increases the difference in the RT of individuals with stuttering 11 once these individuals present difficulties in speech motor planning. Kleinow and Smith 14 , point that the extension of an utterance affects the speech motor planning of stuttering individuals, as well as their motor performance. Therefore, changes in the motor performance as a reaction to the increase in the extension of utterances can contribute to the increase in the variability of movement execution as an attempt to reach an adequate production.…”

The neural substrates for atypical planning and execution of word production in stuttering

“…First, studies of stuttering speakers' motor execution showed aberrant coordination among articulatory, laryngeal, and respiratory systems during both stuttered and fluent speech (e.g., Loucks and De Nil, 2006;Loucks et al, 2007;Max et al, 2003;Namasivayam and van Lieshout, 2008). Second, studies of linguistic factors related to the speech planning process revealed altered semantic, syntactic, and especially phonological processing in both child and adult stuttering speakers, even in the absence of any speech production requirements (e.g., Cuadrado and Weber-Fox, 2003;Kleinow and Smith, 2000;Ratner and Sih, 1987;Sasisekaran et al, 2006;Weber-Fox, 2001;Weber-Fox et al, 2004). Finally, there is also evidence indicating an atypical interface between planning and execution processes (e.g., Blomgren and Goberman, 2008;Dworzynski et al, 2004;Savage and Howell, 2008;Snyder et al, 2009).…”

Influences of rate, length, and complexity on speech disfluency in a single-speech sample in preschool children who stutter

“…Whereas specific information regarding underlying motoric processes cannot be inferred from surface analyses of disfluent speech (Kent, 1996;Kleinow & Smith, 2000;van Lieshout, Hulstijn, & Peters, 2004), the theory of coordination dynamics could provide one explanation for the variability in the two speech samples. Control of motor systems, according to this theory, is achieved through coupling, for example, between articulators (Kelso, 1995).…”