اثر ساختار نحوی بر بار شروع سخنرانی سخنرانان دارای لکنت زبان و غیرلکنت زبان

Past research has shown that adults who stutter tend to be slower than adults who do not stutter at initiating various speech-like movements, nonsense syllables, words, short phrases, and simple sentences. The present study sought to extend this research by examining the effect that syntactic structure has upon stutterers’ and nonstutterers’ ability to initiate sentences. Eleven persons who stutter (mean age=22.2 years) and 11 nonstuttering controls (mean age=23.3 years) read, rehearsed, and then reproduced a series of 96 sentences within a simple reaction time paradigm. The sentences were presented in four blocks of 24 sentences, and each block contained one version of each of the 24 base sentences. Versions of the base sentences varied, from simple to complex, along four levels of syntactic complexity. Results indicated that speech initiation times (SITs) were significantly longer for participants who stutter than they were for nonstuttering controls for three of the four sentence types. There was no significant difference in SITs across the four sentence types for either group. Among the stuttering participants, there was no significant correlation between stuttering severity and overall initiation time for the sentences. Consistent with other studies, the present findings suggest that persons who stutter are slower than persons who do not stutter at planning and/or initiating motor movements associated with speech production. Educational objectives: The reader will be able to (1) describe how persons who stutter typically perform during various reaction time tasks, (2) explain the rationale for examining the effect of syntactic complexity upon speech initiation time, (3) discuss how the speech initiation times of persons who stutter compare to those of persons who do not stutter during the production of various types of sentences, (4) identify future research needs in this area.

Numerous studies have been conducted to examine the role of the motor system in stuttering. In many of these studies, researchers have used so-called simple reaction time tasks to compare stuttering and nonstuttering speakers in their ability to initiate various responses to linguistic and non-linguistic stimuli. Overall, the findings from this body of research suggest that persons who stutter tend to take more time than persons who do not stutter to initiate such responses. For example, findings from some studies suggest that persons who stutter are slower than persons who do not stutter at initiating simple, speech-related behaviors such as lip closing gestures and V, CV, VCV syllables (Adams & Hayden, 1976 and Bakker & Brutten, 1989; Bishop, Williams, & Cooper, 1991; Cross & Luper, 1979; Cross, Shadden, & Luper, 1979; Dembowski & Watson, 1991, Horii, 1984, Maske-Cash & Curlee, 1995 and McFarlane & Prins, 1978; Prosek, Montgomery, Walden, & Schwartz, 1979; Starkweather, Franklin, & Smigo, 1984; Starkweather, Hirschman, & Tannenbaum, 1976; Watson & Alfonso, 1987 and Williams & Bishop, 1992; and see Adams, Freeman, & Conture, 1984, for a review). Findings from other studies suggest that persons who stutter are slower than persons who do not stutter at initiating words, phrases, and short sentences in response to auditory and/or visual cues to begin speaking (Reich, Till, & Goldsmith, 1981; Watson et al., 1991). Further, some researchers have reported that the between-group discrepancy in response initiation time seems to increase with the length of the target response (Peters, Hulstijn, & Starkweather, 1989). Although such studies offer insight into the ability of persons who stutter to rapidly initiate vocal and non-vocal behaviors, they are somewhat limited because, for virtually all of the studies, the target responses required of participants have been much simpler than those typically produced during conversation. Accordingly, it is difficult to determine the extent to which findings from this body of research generalize to the longer, more complex sentences that adolescent and adult speakers routinely produce during daily activities. In those studies where researchers have examined initiation times using linguistically based responses (e.g., Bishop et al., 1991; Maske-Cash & Curlee, 1995, Peters et al., 1989, Reich et al., 1981 and Watson et al., 1991), factors such as response length and syntactic structure have not been controlled or systematically manipulated in relation to one another. Results from studies with nonstuttering adults (e.g., Ferreira, 1991; Sternberg, Monsell, Knoll, & Wright, 1978) suggest that speakers’ response initiation times are sensitive to these factors. Thus, based on the research to date, it is difficult to determine the extent to which linguistic factors contribute to the response initiation profiles seen in persons who stutter. The effect of linguistic demands upon speech-motor control and speech fluency has been a topic of interest in stuttering literature for roughly two decades. Both children who stutter and children who do not stutter have been found to speak less fluently when they produce utterances containing developmentally advanced or relatively many syntactic structures (Gordon & Luper, 1989, Logan & Conture, 1997 and Ratner & Sih, 1987). In addition, both stuttering and normally fluent children and adults have shown greater spatio-temporal variability for motor movements associated with syllables that are produced within syntactically complex environments than they do when the same syllables are produced within syntactically simple environments (Kleinow & Smith, 2000; Maner, Smith, & Grayson, 2000). Thus far, no study has examined the effect of syntactic structure upon the ability of persons who stutter to rapidly initiate speech. In light of the previously demonstrated effects of syntactic complexity upon stuttering speakers’ speech fluency and spatio-temporal stability in speech-motor movements, one might expect that syntactic complexity will also affect their ability to rapidly initiate sentences. The purpose of the present study was to examine the effect of syntactic complexity upon stuttering speakers’ speech initiation times (SITs). To address this purpose, we adapted a procedure used by Ferreira (1991) in a study of syntactic effects upon the SITs of typical adult speakers. In Ferreira’s study, speakers read and rehearsed a series of individually presented sentences, repeating each back as soon as possible when prompted on a computer screen to do so. Ferreira defined syntactic complexity in terms of the number of syntactic nodes within the phrase structure tree that corresponded to a particular sentence. Results showed that the speakers’ initiation times for sentences that featured relatively few syntactic nodes were significantly shorter than those for length-matched sentences that featured relatively many syntactic nodes. Differences among sentence types were on the order of 100 ms, with the more complex sentences taking approximately 650 ms to initiate, and the less complex sentences taking about 550 ms to initiate. Results also suggested that subjects’ SITs were affected primarily by the syntactic complexity of a sentence’s subject constituent. Speakers did not appear to initiate sentences that featured syntactically complex object constituents more slowly than sentences that featured syntactically simple object constituents. Instead, syntactic elaboration of the object constituent was associated with an increase in the duration of any pauses that immediately preceded the main verb of the sentence. Although other metrics of syntactic complexity have been proposed in recent years (e.g., Gibson, 1998), the node based approach used by Ferreira seemed like an appropriate way to examine the issues of interest in this study, given its previously demonstrated ability to differentiate sentence initiation times. In summary, the present study was conducted to determine the effect of syntactic structure upon the ability of persons who stutter and persons who do not stutter to promptly initiate sentences. Based upon previous findings, we hypothesized that persons who stutter would take longer than persons who do not stutter to initiate sentences. In light of Ferreira’s (1991) results and the previously reported associations between syntactic complexity and speech production with persons who stutter, we also hypothesized that speakers would take longer to initiate syntactically complex sentences than they would to initiate syntactically simple sentences and that the performance differences between persons who stutter and persons who do not stutter would be greatest for the production of linguistically complex sentences (i.e., those sentences containing relatively many syntactic nodes). The research questions of primary interest were as follows: Do persons who stutter differ from persons who do not stutter in the time they take to initiate sentences? Does syntactic complexity affect the speed at which speakers initiate sentences? If so, are the initiation times of persons who stutter affected by syntactic complexity to a greater extent than those of persons who do not stutter?