Effects of sentence-structure complexity on speech initiation time and disfluency

Journal of Fluency Disorders 38 (2013) 30–44

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Journal of Fluency Disorders

Effects of sentence-structure complexity on speech initiation time and disfluency Jim Tsiamtsiouris a,∗ , Helen Smith Cairns b a b

William Paterson University, United States Queens College and the Graduate Center of the City University of New York, United States

a r t i c l e

i n f o

Article history: Received 10 September 2012 Received in revised form 6 December 2012 Accepted 9 December 2012 Available online 5 January 2013

Keywords: Sentence structure Speech initiation time Adults who stutter

a b s t r a c t There is general agreement that stuttering is caused by a variety of factors, and language formulation and speech motor control are two important factors that have been implicated in previous research, yet the exact nature of their effects is still not well understood. Our goal was to test the hypothesis that sentences of high structural complexity would incur greater processing costs than sentences of low structural complexity and these costs would be higher for adults who stutter than for adults who do not stutter. Fluent adults and adults who stutter participated in an experiment that required memorization of a sentence classified as low or high structural complexity followed by production of that sentence upon a visual cue. Both groups of speakers initiated most sentences significantly faster in the low structural complexity condition than in the high structural complexity condition. Adults who stutter were over-all slower in speech initiation than were fluent speakers, but there were no significant interactions between complexity and group. However, adults who stutter produced significantly more disfluencies in sentences of high structural complexity than in those of low complexity. Educational objectives: After reading this article, the learner will be able to: (a) identify integral parts of all well-known models of adult sentence production; (b) summarize the way that sentence structure might negatively influence the speech production processes; (c) discuss whether sentence structure influences speech initiation time and disfluencies. © 2012 Elsevier Inc. All rights reserved.

1. Introduction Stuttering affects approximately 1% of the world’s population at any given time, and approximately 5% will experience it at some point in their lives (Bloodstein & Ratner, 2008). Having this communication disorder is a potentially devastating experience, affecting speech, language, social, academic, and occupational function in adults. After decades of research, there is general agreement that stuttering is caused by a variety of factors and their interaction; no single factor has been identified for all people who stutter (Kent, 2000; Smith & Kelly, 1997). Main factors appear to center around language formulation (e.g., lexical retrieval, syntactic construction, phonological encoding) and motor processes of speech, and there is suspicion that subgroups exist within the population of speakers who stutter (Kent, 2000; Tsiamtsiouris & Cairns, 2009; Watson et al., 1991). There are at least two reasons why it is important to increase our understanding of the different factors that lead to or maintain stuttering. First, from a theoretical perspective, we need to improve our understanding of the speech and

∗ Corresponding author at: Department of Communication Disorders, William Paterson University, 300 Pompton Road, Wayne, NJ 07470, United States. Tel.: +1 973 720 3355. E-mail address: [email protected] (J. Tsiamtsiouris). 0094-730X/$ – see front matter © 2012 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.jfludis.2012.12.002

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language processes that are unique to people who stutter and the potential effects that the various components may have on fluency. Second, understanding these processes has the potential to influence the way we evaluate and treat stuttering in clinical settings. The current study investigated the language formulation basis of stuttering. In particular, the aim was to assess the effects of sentence structure on variables such as speech initiation time and disfluency. In the sections that follow, we describe what is known about sentence construction mechanisms, and, in particular, the syntactic skills of individuals who stutter. 1.1. Sentence construction mechanisms The generation of sentence structure is an integral part of all well-known models of adult sentence production (Bock & Levelt, 1994; Garrett, 1988; Levelt, 1989). The first step of sentence construction is the formulation of an abstract idea. Then, sentence planning mechanisms must select the correct words (from the speaker’s lexicon) and create the correct syntactic structure (based on the speaker’s grammar) to convey the desired sentence meaning (Fernandez & Cairns, 2010, chap. 5). Grammatical encoding can be divided into functional processing and positional processing (Bock & Levelt, 1994; Garrett, 1988). Functional processing involves lexical and lemma selection. Information associated with a lexical item involves conceptual properties (domestic animal, four legs, fur, etc.), whereas lemmas contain grammatical information such as form class (content or function word, noun, verb, etc.) and subcategorical restrictions (whether a verb can be followed by an object, a clause, etc.). After the selection of appropriate lemmas, functional assignment calls for assigning syntactic relations or grammatical functions to the words (Bock & Levelt, 1994). In other words, the speaker’s sentence production mechanism must specify the words that will serve as the subject of the sentence and which, if any, will serve as predicates of various kinds. Additional processing is required after the selection of lemmas, as the elements of an utterance need to be organized into a syntactic structure. This occurs in a subcomponent of positional processing, called constituent assembly. The result of these operations is a sentence structure of hierarchically ordered syntactic elements based on the speaker’s grammar. This structure, together with the selected lexical items, conveys the meaning of the sentence. Despite the automaticity of these steps, sentence planning incurs processing costs, which vary with the complexity of the sentence. As the planned sentence is sent to the speech production system, complexity interacts with the motor systems involved in the actual production of the sentence (Kleinow & Smith, 2000; Namasivayam & Van Lieshout, 2011). Processing cost arises from the deployment of cognitive (psycholinguistic planning and execution) and physical (motor planning and execution) resources by the speaker (Kleinow & Smith, 2000; Tsiamtsiouris & Cairns, 2009). 1.2. Effects of processing cost on speech production Support for the view that speech and language factors are centrally implicated in stuttering comes from two types of studies. The first type involves the measurement of brain activity in specific areas in response to language processing. Such studies, in the absence of overt speech, demonstrate atypical semantic and syntactic processing in adults who stutter when compared to adults who do not stutter (Cuadrado & Weber-Fox, 2003; Weber-Fox, 2001; Weber-Fox, Spencer, Spruill, & Smith, 2004). Other studies show atypical brain functions in areas related to speech, language, and auditory processing, supporting the hypothesis that language processing operates differently in individuals who stutter than in individuals who do not (Braun et al., 1997; Fox et al., 1996, 2000; Ingham, Fox, Ingham & Zamarripa, 2000; Preibisch et al., 2003). Another type of study experimentally manipulates linguistic variables and examines the effects of these variables (Kleinow & Smith, 2000; Melnick, Conture, & Ohde, 2003; Pellowski & Conture, 2005; Ratner & Sih, 1987; Silverman & Ratner, 1997) on characteristics of speech. A small number of these studies have focused on syntactic variables such as sentence structure in order to study the effects of increased processing cost on aspects of speech production such as speech initiation (Anderson & Conture, 2004; Tsiamtsiouris & Cairns, 2009). One of the first studies (Johnson, 1966) to investigate the effects of syntactic complexity on speech initiation time involved sentences that differed according to the branching structure or hierarchical tree of the utterance. Some sentences had a more right branching structure or fewer syntactic nodes, and other sentences had more nodes and a more complex branching structure. This early study (Johnson, 1966) found that syntactic complexity affects speech initiation time, thereby supporting the notion that there are processing costs associated with the generation of sentence structure. Tsiamtsiouris and Cairns (2009) employed Ferreira’s (1991) experimental paradigm to measure the processing cost of sentence structure generation in adults who stutter and to test the hypothesis that this cost would be higher for adults who stutter than for adults who do not stutter. Participants saw a sentence, committed it to memory, and then verbally produced it after the sentence was removed and a cue prompted the person to start speaking. Sentence initiation time was measured; sentences were of either high or low syntactic complexity. The high complexity sentences contained a relative clause in the subject Noun Phrase (NP) and an additional relative clause after the main verb; the low complexity sentences were identical except for the fact that there was no relative clause in the subject NP. Instead, low complexity sentences had adjectives that preceded the subject. Length was controlled, as both sentence types were approximately 20 syllables long. Results for both groups of speakers revealed that speech initiation time was greater for high complexity sentences than for low complexity sentences. However, the difference was significantly greater for the people who stutter than for the fluent control group. These results confirmed the authors’ hypothesis that grammatical encoding costs would be more detrimental to adults who stutter than to the fluent participants, giving support to the theory that psycholinguistic factors are implicated in stuttering.

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Logan (2003) conducted a study with a similar experimental paradigm, but failed to show the differential processing cost of grammatical complexity for adults who do and do not stutter. The crucial difference between his sentences and those of Tsiamtsiouris and Cairns (2009) was that his were shorter and simpler. This suggests that there is a cost threshold that must be exceeded in order to observe a sentence structure complexity effect on speech initiation time in adult speakers; after this threshold is crossed, adults who stutter are more adversely affected than adults who do not stutter. Silverman and Ratner (1997) conducted a study that had some methodological similarities to Logan (2003) and Tsiamtsiouris and Cairns (2009). These studies manipulated sentence structure complexity by incorporating a relative clause into the subject NP, defining this sentence type as high complexity. Sentences without relative clauses were considered lower in complexity. A major difference among the studies was the overall complexity level in terms of sentence structure and length. Tsiamtsiouris and Cairns’ (2009) sentences had two embedded relative clauses and approximately 20 syllables, whereas Silverman and Ratner’s (1997) and Logan’s (2003) had only one relative clause and approximately 11 syllables. All three studies controlled for sentence length. Another difference was the dependent variables. Instead of speech initiation time, Silverman and Ratner (1997) analyzed disfluencies and inaccuracies. Both speaker groups in Silverman and Ratner’s study (1997) produced significantly more of these when imitating the high complexity sentences than when imitating the low complexity sentences. As in the Logan (2003) study, there was not a significant difference between speaker groups, reinforcing the hypothesis that sentences must exceed a threshold of complexity before there is a greater impact of complexity on adults who stutter than adults who do not stutter. However, the fact that both speaker groups produced more disfluencies and inaccuracies in the high relative to the low complexity sentences constitutes support for the hypothesis that increased complexity of the sentence structures creates an increased processing cost, leading to increased stress on the speech production system in all speakers. Early work with typical adult speakers has connected normal disfluencies with the complexity of the speech planning task and the onset of clauses (Beattie, 1980; Boomer, 1965; Butterworth, 1980; Ford, 1978; Goldman-Eisler, 1972). This has led to the belief that the beginnings of clauses are critical planning junctures and areas of increased processing cost for children and adults (Bernstein, 1981; Bock, 1996; Garrett, 1982; McDaniel, McKee, & Bernstein, 1998; McDaniel, McKee, & Garrett, 2010; McKee & McDaniel, 2001; Wall, Starkweather, & Cairns, 1981). In children, normal disfluencies at these points seem to be related to the ease with which fluent speakers can generate sentence structure (Wijnen, 1990, 1992; Rispoli & Hadley, 2001). Research with people who stutter has shown us that sentence structure has the potential to negatively influence the speech production processes (Kleinow & Smith, 2000; Tsiamtsiouris & Cairns, 2009). There are a number of explanations for the increased sensitivity of people who stutter to sentence length and complexity (Starkweather & Gottwald, 1990; Wall et al., 1981). The beginnings of sentences and clause boundaries have shown an increased likelihood of stuttering (Brown, 1938, 1945; Silverman & Williams, 1967). Wall et al. (1981) showed a significant relationship between clause boundaries and location of stuttered events in children. Moreover, if sentence length is held constant, speakers who stutter have a tendency to exhibit more stuttering on the initial clause of a sentence than on the same clause in the final position of a sentence (Jayaram, 1984). A plausible explanation for these observations is that as speakers plan aspects of utterances and clauses prior to actual speech articulation (Garrett, 1975; Levelt, Roelofs, & Meyer, 1999), processing costs associated with this activity tax or overload the resources available for fluent speech production (Bosshardt, 1995; Starkweather & Gottwald, 1990; Yaruss, 1999). In other words, fluency breakdowns may occur if demands exceed a speaker’s threshold or capacity for fluent speech. This is reminiscent of Rispoli’s (2003) suggestion that children have a comfort zone in which it is easy to plan and produce linguistic information. If there are linguistic demands beyond the comfort zone, fluency can be compromised. In other words, if the cost to plan and produce syntactic structures is high, then construction of a sentence with complex structure has the potential to overwhelm the speech production system (Kleinow & Smith, 2000). The outcome is a breakdown in the coordinated functioning of the various speech and language systems that are essential for speech motor stability, initiation of speech, and fluency (Garrett, 1982; Kleinow & Smith, 2000; Namasivayam & Van Lieshout, 2011; Rispoli & Hadley, 2001; Tsiamtsiouris & Cairns, 2009). Another line of inquiry has focused on whether people who stutter have an innate limitation (e.g., lower end of normal) of the speech motor control system and how this system is influenced by interactions with cognitive, linguistic, emotional, speech motor tasks (Peters, Hulstijn, & Van Lieshout, 2000). According to this model, an increase in processing cost or task complexity taxes a vulnerable speech motor control system and requires a speaker to use additional resources from a finite pool of central resources (Smits-Bandstra & De Nil, 2007; Van Lieshout, Hulstijn, & Peters, 2004). The strain that is placed on a vulnerable system can lead to speech motor control instability and an increase in disfluencies and other speech-related changes. It should be noted that in this model the speech motor control system of people who do not stutter is also taxed when there is an increase in processing cost; however, the main difference is that these individuals can handle the demands without a deleterious impact on fluency (Namasivayam & Van Lieshout, 2011). 1.3. Sentence structure and the manipulation of processing cost In the current study, our goal was to create two lists of low and high complexity sentence types while controlling for length. It was hypothesized that sentential complexity would influence speech initiation time and disfluency in adults who do and do not stutter. A review of the psycholinguistic literature revealed an abundance of studies that investigated the impact of different sentence types on comprehension, but very few studies that examined the impact on production. Therefore,

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we will briefly discuss sentence types used in comprehension studies, as these sentence types will form the basis for our production study. Comprehension complexity can arise from many sources and is relevant to address particular theories of the operation of the structural processor (the parser) of the hearer. The parser creates a structural analysis of a heard sentence, which is necessary in order to recover the meaning encoded by the speaker (Fernandez & Cairns, 2010, chap. 7). Comprehension complexity can arise from increasing demands on sentence integration and working memory; processing elements that depart from canonical subject-verb-object order of grammatical relations; and processing elements with long distance dependencies. All of these factors increase the processing costs on the comprehension system. Below we describe different sentence types (low complexity paired with high complexity) that have been demonstrated to increase processing costs; these sentence types were used in the current production study. 1.4. Sentences with a relative clause in its subject noun phrase A sentence that contains a clause (in this case a relative clause) is of greater complexity than one that does not. This is because the presence of a clause creates a constituent in the sentence structure not present in a sentence without a clause. Literature cited above implicates an association between clauses and disfluencies. Our first complexity pair contrasts a sentence with a relative clause in its subject Noun Phrase (e.g., “The plane that was leaving climbed higher into the sky that was clear and blue”) to one that does not (e.g., “The small but mighty plane climbed higher into the sky that was clear and blue). These sentence types have been used in two studies, Ferreira (1991) and Tsiamtsiouris and Cairns (2009), both measuring speech initiation times, the latter also measuring stutter-like disfluencies. 1.5. Sentences with subject–object relative clauses Sentences containing subject–object relative clauses (e.g., “The boy who the cat scratched cried”) are more costly to process than those containing object–subject relative clauses (e.g., “The boy petted the cat who purred.”). These sentence types have been studied extensively in comprehension, demonstrating the greater comprehension costs associated with subject–object relative clauses (Carpenter, Miyake, & Just, 1994; Ford, 1983; Gibson, 1998; Holmes & O’Reagan, 1981). In the more complex sentence type, containing subject–object relative clauses, the subject Noun Phrase (“the boy” in our example) is modified by a relative clause that intervenes between it and its verb (“cried”) and plays two grammatical roles, the subject of “cried” and the object of “scratched” (between which four words intervene). In the less complex sentence type, containing an object–subject relative clause, the relative clause modifies the object (“the cat”), which plays two grammatical roles, the object of “petted” and the subject of “purred;” both can be processed simultaneously, as there are no intervening words. Another major difference between the two sentences is that in the subject–object relative “the boy” is the object of “scratched,” giving the relative clause a non-canonical object–subject-verb order of grammatical relations, which is not the case with the other sentence. There are, then, a number of reasons why processing costs are greater for sentences containing a subject–object relative clause than those containing an object–subject relative clause. 1.6. Sentences with an initial subordinate clause, followed by a main clause It is more difficult to process a sentence that consists of an initial subordinate clause, followed by a main clause (e.g., “When the plane landed on the ground, the captain welcomed everyone to New York.”) than one that consists of an initial main clause followed by a subordinate clause (e.g., “The captain welcomed everyone to New York when the plane landed on the ground.”). There is abundant evidence from the comprehension literature that initial subordinate clauses are processed less completely than are initial main clauses (Bever & Townsend, 1979; Garnham, Oakhill, & Cain, 1998; Jarvella, 1971; Townsend & Bever, 1978). This is because a main clause does not depend on a following subordinate clause for its meaning, therefore it can be completely processed. A subordinate clause depends on the main clause for its meaning, so it cannot be completely processed until the main clause is received. Anytime incompletely processed information must be held in memory processing costs are incurred. For this reason, sentences with a subordinate–main clause word order incur more processing costs than do sentences with main–subordinate order. 1.7. Sentences in the passive voice Sentences in the passive voice (e.g., “The small dog was chased by the black cat down the busy city street.”) incur more processing costs than do those in the active voice (e.g., “The black and white cat chased the small dog down the busy city street.”). Passive sentences have been studied throughout the history of psycholinguistics because they are a classic example of a sentence that violates the English canonical (standard) subject-verb-object order of grammatical elements. In this structure the object of the verb has moved to fill the subject position of the sentence, forming an argument chain between the object and subject positions. As in subject–object relative clauses, a single Noun Phrase serves simultaneously as subject and object of a verb. Passive sentences are known to be produced very late by English speaking children (Horgan, 1978); they are also difficult for young children to comprehend (Strohner & Nelson, 1974). Studies also show that passive sentences are more costly for adults to process than are active sentences (Gough, 1966; Mehler, 1963).

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1.8. Sentences with verb phrase complements In both verb phrase complements (e.g., “The teacher told the students in the room to sit down and be quiet.”) and adverbial adjunct clauses (e.g., “The child played with the toy while waiting for his mom to return.”), clausal subjects (of “to sit” and “waiting”, respectively) must be inferred from the structure of the sentence. There has been extensive study of the comprehension of these forms by children (Cairns, McDaniel, Hsu, & Rapp, 1994; Hsu, Cairns, & Fiengo, 1985); VP complements are correctly interpreted at a much earlier age than are adverbial adjuncts. In fact, young children incorrectly interpret the object of the adverbial adjuncts as being the object of the main clause, in an analogy to the VP complements. There is no evidence that adults incur greater processing costs with adverbial adjuncts than with VP complements; however, the difference in children’s interpretation of the two structures suggested to us that those with adverbial adjunct clauses may be of greater complexity, so we included them in our study. 1.9. Summary and research questions In summary, research with people who stutter has shown us that sentence structure has the potential to negatively influence the speech production processes, and a number of studies have identified a variety of low and high complexity sentence types that influence processing cost. Most of these studies that manipulated complexity to examine processing cost have focused on comprehension, and it remains to be seen whether these sentence types show a higher processing cost during sentence production. The hypothesis that high complexity sentences will create longer speech initiation times and more disfluencies than low complexity sentences has important implications for psycholinguistic theory. Confirmation would suggest a processing connection between the comprehension and production systems. In addition, if effects of complexity are more pronounced for adults who stutter than for people who do not stutter, this result will constitute additional evidence for theories of stuttering that implicate sentential complexity in people who stutter. The research questions for this study were the following: (1) Do all speakers initiate low complexity sentences significantly faster than high complexity sentences? (2) Do adults who stutter initiate all sentences significantly more slowly than adults who do not stutter, regardless of complexity? (3) Does sentence complexity have a greater impact on the speech initiation time of adults who stutter than on adults who do not stutter? (4) Do all speakers produce low complexity sentences with significantly fewer disfluencies than high complexity sentences? (5) Does sentence complexity have a greater impact on speech disfluencies in adults who stutter than adults who do not stutter? 2. Method 2.1. Participants Participants were 21 adults who stutter (M = 29.33 years; SD = 6.85 years) and 21 adults who did not stutter (M = 29.42 years; SD = 7.40 years). Every individual in the experimental group (17 males, 4 females) was matched for age (±3 years), gender, and education with an adult who did not stutter. All individuals had at least some college education. Both groups of speakers were required to have American English as their primary language and general language skills that passed several screening measures. The language screening measures included a language background questionnaire, a 15-min spontaneous speech-language sample, and three subtests (1. Word Opposites; 2. Word Derivations; 3. Sentence Combining) of the Test of Adolescent and Adult Language, Fourth Edition (TOAL-4; Hammill, Brown, Larson, & Wiederhold, 2007). The TOAL-4 is standardized and normed for adults through age 24 years and 11 months. Passing scores for all participants were based on normal values for this age. The 15-min spontaneous speech-language sample was a language measure that was used for an informal analysis in three areas: syntax (errors in word order, tense, and aspect), semantics (errors in word use), and pragmatics (errors in turn-taking). A pass on this measure consisted of less than 2 errors in each area. All participants passed this screening measure. The background questionnaire asked subjects about their ability to speak a language other than English, general knowledge and competence within each language, history of speech, language, learning, or hearing disorders, and whether they received a speech-language evaluation or speech-language therapy in the past. Subjects did not pass this screening if they indicated any history of a communication or learning disorder other than stuttering. Moreover, subjects failed if they indicated that English was not their primary language. For adults who stutter, information was gathered on whether they were currently enrolled in therapy or participated in stuttering support groups. As expected, the questionnaire revealed that all adults who stutter had received a variety of therapy over the years in the past, but none were enrolled in individual therapy at the time of this study. Approximately half of the stuttering participants were involved with stuttering support groups. If any subject failed the language screening measures described above, then they were excluded from participation. The rationale behind this procedure was to exclude subjects with gross language deficits or a weak knowledge of English. Four adults who stutter who volunteered for the study were not allowed to proceed with the study because they did not pass the language screening measures. Participants in the experimental group were required to score at least a “mild” (i.e., total overall score = 11 or above) on the Stuttering Severity Instrument-Third Edition (SSI-3; Riley, 1994). The same 15-min speech-language sample mentioned in the previous paragraph was used for the SSI-3. A graduate student of communication disorders trained by the first author

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conducted the above assessments. The mean SSI-3 score for the participants who stuttered was 23.38. Based on this test, 12 individuals were classified as mild and 9 as moderate stutters. 2.2. Design and materials The main design of the study consisted of 36 low complexity sentences paired with 36 high complexity sentences. The low and high complexity sentences consisted of five different sentence types, as described in the previous section and described again at the end of this section. The low complexity (M = 18.42; SD = 2.28) and high complexity (M = 18.5; SD 2.33) sentences were matched for number of syllables and did not differ significantly in length, t(35) = −.173, p = .864. Two counterbalanced sets of sentences were created, Set A and Set B (Appendix A and B). Each participant heard one of the two sets. Set A contained half the sentences in their low complexity versions and the other half in their high complexity versions. The sentences that appeared in their low complexity version in Set A appeared in their high complexity versions in Set B, and, similarly, those that appeared in their high complexity versions in Set A appeared in their low complexity versions in Set B. Thus, each participant heard equal numbers of high and low complexity sentences, and each sentence appeared in both its low and high complexity version (across participant groups). High and low complexity versions of each sentence were equated for length as calculated in syllables and had identical lexical content. Below are examples of the five different sentence types that were used to create the low/high complexity pairs while controlling for length. We indicate the materials set in which each appears to illustrate our counter-balancing procedure. 1a. Less complex (no clause in subject Noun Phrase): The strong and agile coyotes hunt in the hills that are next to the lake. (Set A) 1b. More complex (relative clause in subject Noun Phrase): The coyotes that are hungry hunt in the hills that are next to the lake. (Set B) 2a. Less complex (contains an object–subject relative clause): The bird ate the worm that crawled across the ground and into the nest. (Set A) 2b. More complex (contains a subject–object relative clause): The worm the bird ate crawled across the wet ground and into the nest. (Set B) 3a. Less complex (main clause precedes subordinate clause): The superintendent closed the schools due to the snowstorm and high gusty winds. (Set B) 3b. More complex (main clause follows subordinate clause): Due to the snowstorm and high gusty winds, the superintendent closed the schools. (Set A) 4a. Less complex (active voice): The clever fox chased the small fast mouse and ran quickly into the woods. (Set B) 4b. More complex (passive voice): The fast mouse was chased by the clever fox and ran into the woods. (Set A) 5a. Possibly less complex (contains VP complement): The dog wanted to drink the water from the bowl next to his dish. (Set B) 5b. Possibly more complex (contains adverbial adjunct clause): The dog ate the food after drinking the water that was in the bowl. (Set A) 2.3. Procedure Participants sat in front of a computer monitor in a quiet room with no distractions and were instructed to maintain a constant distance of six inches from a microphone. They were naïve as to the purpose of the study. Instructions were given verbally as well as visually on the computer screen, and five practice sentences were presented prior to the start of the experiment. The experimenter provided feedback and invited questions during the practice portion. Participants were allowed to proceed to the experimental sentences after they completed the practice portion with 100% accuracy, and stated that they understood the procedures for the experimental trials. Each trial consisted of the following steps. A message appeared on the screen that prompted the participant to push a button to indicate that he or she was ready for a sentence to appear on the screen. A sentence appeared after the button push. The participant memorized the sentence and pushed the button again after he or she felt confident enough to repeat the sentence accurately. Upon the second button push, the sentence disappeared from the computer screen. After a random delay varying from 500 to 1000 ms, the statement “Say the sentence now” appeared on the screen. The appearance of the statement on the screen was the participant’s cue to begin saying the sentence as quickly and as accurately as possible. The rationale for having participants hold the sentence in short-term memory and then produce it following a delay, as opposed to simply having them imitate or read the sentence was that it was more similar to the spontaneous production of a sentence. Repetition required participants to recreate the structure of the sentence. Speech initiation time was defined as the time elapsed between presentation of the statement and the onset of the subjects’ audible speech. Each person spoke into a microphone, which was used to trigger the voice-activated relay interfaced with the microphone and desktop computer. E-prime software controlled the steps of each trial and gathered speech initiation times. The trials continued until the completion of all 36 sentences. The experimenter sat behind the participant and listened to the production of each trial for each participant. All sentences were continuously monitored during the experiment and coded for disfluencies and errors. Errors consisted of missing words,

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Table 1 Mean speech initiation times (in ms) and standard deviations for condition and group. Condition

Low complexity High complexity

Fluent adults

Adults who stutter

Total

M

SD

M

SD

M

SD

610 682

76 78

666 725

81 83

638 703

83 83

incorrect words, incorrect word order, or any inappropriate sound (unexpected interruptions) or vocalization (e.g., coughing, throat clearing, etc.) immediately before or during a trial. Disfluencies were categorized as either “stutter-like” or “typical.” A stutter-like disfluency was operationally defined as a part-word repetition, single-syllable word repetition, or disrhythmic phonation (Yairi & Ambrose, 2005). A typical disfluency was operationally defined as multisyllabic whole word repetition, phrase repetition, interjection, and revision (Yairi & Seery, 2011). If a trial contained any errors or disfluencies, then that trial was excluded from speech initiation time analyses. In order to facilitate reliability analyses, subjects’ verbal production of sentences was recorded with a Marantz Digital Compact Disc Recorder. It should be noted that subjects were told to say the sentences quickly and accurately, but they were not encouraged to use any fluency-enhancing techniques. They remained naïve to the study and were unaware that speech initiation time and disfluency were the dependent variables. Due to the number of trials, the variety of sentence types, and a lack of information regarding the paradigm of the study, the authors assumed that any attempt to use fluency-enhancing techniques by the subjects would be distributed evenly across trials and conditions, thereby washing out any confounding influence. Interjudge reliability for the classification of disfluencies and errors was established by enlisting an independent judge blind to the study to analyze 30% of the entire data set. The first author familiarized the independent judge with the criteria for disfluencies and errors. Interjudge point-to-point reliability for coded responses was 91.6 percent for disfluencies and 97.6 percent for errors. Intrajudge point-to-point reliability measure was 98.4 percent for disfluencies and 100 percent for errors. 2.4. Analyses Two mixed analysis of variances (ANOVA) were conducted, with group association (fluent adult or adult who stutters) as the between-group variable and complexity condition (low and high complexity sentences) as a repeated measures variable. The low and high complexity sentences from Groups A and B were combined into one data set. Dependent variables consisted of speech initiation time of error-free fluent responses and number of disfluencies. Post hoc tests were conducted as appropriate. 3. Results 3.1. Speech initiation time analyses Responses that were produced without disfluencies and errors were analyzed for speech initiation time. Discarded trials resulted in the loss of 5.7% of trials for the fluent adults and 14.7% for adults who stutter. This difference was not a surprising outcome, as adults who stutter had a higher number of sentences with disfluencies. Table 1 displays mean speech initiation times and standard deviations by condition and group. A mixed ANOVA revealed significant main effects of group F(1,40) = 5.098, p = .029 and condition F(1,40) = 33.950, p < .0001, but no significant interaction F(1,40) = .294, p = .590. In light of the main effect of condition with no interaction between group and condition, follow-up t-tests were performed to compare the different sentence types between the two conditions for all speakers. Table 2 displays the results of the t-tests. With the application of a Bonferroni adjustment, four out of the five low-high complexity sentence types showed significant differences. The only sentence type that was not significant was the verb phrase complement-adjunct clause. It is not at all surprising that the comparison of sentences with verb phrase complements with those containing adverbial clauses showed no complexity effect. This comparison comes from the acquisition literature, and, unlike the other sentence types, has never been tested in an experiment with adults in a comprehension study. 3.2. Disfluency analyses Table 3 presents mean number of total disfluencies by group and condition. A mixed ANOVA for number of total disfluencies as the dependent variable revealed a significant effect of group F(1,40) = 129.30, p < .0001 and condition F(1,40) = 28.90, p < .0001, and a significant interaction F(1,40) = 24.79, p < .0001. The significant main effect of group is not a very surprising outcome because one of the speaker groups involved adults who stutter. The interesting outcome is the significant interaction between condition and group. This indicates that sentence structure complexity has a negative impact on all speakers, but it has a greater effect on adults who stutter than on fluent adults. As a result, follow-up t-tests were performed with just adults who stutter to determine if all sentence types exhibited the low-high complexity effect. Table 4 displays mean number of total disfluencies and standard deviations across the five

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Table 2 Mean SITs (in ms) and standard deviations for all adults and associated significance levels. Sentence type

Total

t-Test

M

SD

t

df

Sig.

Low: No clause in NP High: Clause in NP

598 704

104 128

−5.236

41

.0001**

Low: Object–subject High: Subject–object

619 693

117 112

−3.965

41

.0001**

Low: Main–subordinate High: Subordinate–main

611 684

109 133

−3.983

41

.0001**

Low: Active High: Passive

642 752

139 163

.302

41

.0001**

Low: Verb phrase comp High: Adjunct clause

676 668

157 144

−.839

41

.764

**

Significant with Bonferroni correction.

Table 3 Mean number of disfluencies and standard deviations for condition and group. Complexity condition

Low complexity High complexity

Fluent adults

Adults who stutter

Total

M

SD

M

SD

M

SD

3.00 3.52

2.52 4.05

28.48 42.14

11.65 15.75

15.73 22.82

15.34 22.60

Table 4 Mean number of disfluencies and significance levels for adults who stutter. Sentence type

M

t

df

Sig.

Low: No clause in NP High: Clause in NP

6.90 10.80

5.30 7.18

−2.58

20

.018

Low: Object–subject High: Subject–object

5.66 8.76

3.92 4.96

−3.51

20

.002**

7.33 11.42

4.06 5.37

−3.58

20

.002**

Low: Active High: Passive

4.14 6.38

3.21 3.96

−2.71

20

.013

Low: Verb phrase comp High: Adjunct clause

4.42 4.76

3.20 3.01

−0.314

20

.757

Low: Main–subordinate High: Subordinate–main

**

SD

t-Test

Significant with Bonferroni correction.

different sentence types for the group of adults who stutter and the results of the comparisons. With a Bonferroni adjustment, only two of the five sentence types were significant. However, it should be noted that four of the five sentence types were significant without the adjustment. Two additional statistical analyses were conducted in an attempt to determine whether increased complexity of sentences affected both typical disfluencies and stutter-like disfluencies for all speakers. In the analysis of typical disfluencies across all participants, there was a significant difference when low complexity was compared to high complexity, t(1, 41) = −3.627, p = .001. Similarly, stuttering-like disfluencies across all participants revealed a significant difference, t(1, 41) = −3.243, p < .002. This indicated that an increase in complexity increased both typical disfluencies and stutter-like disfluencies in all speakers.

4. Discussion We hypothesized that the production of structurally complex sentences would incur a high processing cost and that this high cost would have an impact on speech characteristics such as initiation time or disfluency. We begin our discussion by reviewing the effects of complexity on speech initiation time and disfluency, and then turn to our thoughts about the theoretical implications of its impact on adults who stutter.

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4.1. Effects of sentence complexity on speech initiation time and disfluency One important finding of this study was that sentence complexity, as measured by a variety of sentence types while controlling for sentence length, affects speech initiation time and disfluency in fluent adults and adults who stutter. Previous research found that these sentence types affected processing load in comprehension but, to the best of our knowledge, this is the first time that all of these different sentence types were tested with the purpose of measuring their impact on aspects of speech production (i.e., speech initiation and disfluency). In addition to examining overall complexity, it is interesting to look at the impact of the different sentence types. The first comparison was between a sentence with a relative clause in the subject Noun Phrase and one with no clause. Tsiamtsiouris and Cairns (2009) reported that the former, being more complex, increased speech initiation time for both fluent speakers and those who stutter. The present study supported this finding. However, in terms of disfluencies, with the Bonferroni adjustment adults who stutter did not show a significant increase in disfluencies. With the exception of one comparison (verb phrase complement versus adjunct clause), the complex versions of the other sentence types also increased initiation times for both speaker groups. However, the group of adults who stutter mirrored the fluent adults with the complexity effect. In contrast, there was a significant interaction between group and complexity for disfluencies, thereby indicating that sentence complexity has a greater impact on adults who stutter than it does on fluent adults. The subject–object and subordinate–main sentence types appeared to create the greatest difficulty for adults who stutter, and they were the only two that produced differences significant with the Bonferroni adjustment. However, the passive sentences and those with relative clauses in the subject NP were highly significant without the adjustment, unlike the comparison of sentences with verb phrase complement versus those with an adjunct clause. We must hold open the possibility that the Bonferroni adjustment has resulted in a Type 2 error and further research will show an effect of these two sources of complexity. The results of this study appear to support previous findings of increased disfluencies in sentences of higher syntactic complexity than in sentences of lower complexity (Silverman & Ratner, 1997) in speakers who do and do not stutter.

4.2. Theoretical implications We now turn to the theoretical implications of these findings on the speech production system of fluent adults and adults who stutter. This study confirms a general theory of speech production in which sentence construction takes place at different levels of planning before speech is produced (Bock & Levelt, 1994; Fernandez & Cairns, 2010, chap. 5; Garrett, 1988; Levelt, 1989; Levelt et al., 1999). Grammatical encoding, or the creation of sentence structure, is one component of sentence planning that can be manipulated in an attempt to determine whether there is an impact on speech production (Ferreira, 1991; Levelt et al., 1999; Smith & Wheeldon, 2001; Tsiamtsiouris & Cairns, 2009). Speech initiation time is a variable that appears to reflect the cost of cognitive (psycholinguistic planning and execution) and physical (motor planning and execution) resources by the speaker. Our interpretation of the results of the current study is that the slower speech initiation times in complex sentences, relative to simpler sentences, is due to the increased processing cost placed on the speech production system at the point where the grammatical form of the sentence is planned. A sentence that carries a higher cost within the psycholinguistic system has an increased chance of relaying this cost to the speech motor system. The model proposed by Namasivayam and Van Lieshout (2011) and others (cited above) accounts elegantly for this effect. In a person who stutters the cost of organizing a sentence with complex structure taxes an innately limited speech motor control system, leading to speech motor control instability and an increase in disfluencies and other speech related changes (in this case, speech initiation times). An aspect of this study of general psycholinguistic interest is that it employed a wide range of sentences types not previously tested, and that structural complexity increases the time required to initiate speech both for people who do and do not stutter. In addition, structural complexity appears to have an impact on typical and stutter-like disfluencies in the same way when all speakers are examined. All speakers show an increase in disfluency in the high complexity sentence types, and the increase is significant for both typical and stutter-like disfluencies. However, the increase in complexity also leads to a greater degree of disfluencies in adults who stutter relative to fluent adults. Conture (2001) describes the speech, language, and motor systems as highly efficient and rapid with a specific and orderly chain of events. The timely or untimely processing of these events and the processing cost can cascade down to the next level (Conture, 2001), as accounted for by the Namasivayam and Van Lieshout model. Conture et al. (2006) describe a Communication-Emotional Model of Stuttering in which they implicate speech and language processing (planning and production) as key variables in stuttering and suggest that slow and inefficient encoding of linguistic variables may set the stage for stuttering. The slow and inefficient encoding of complex structures burdens the speech motor system (articulatory processes) with minor delays that result in temporal timing problems. A demand in one component (Starkweather & Gottwald, 1990), such as that resulting from quickly recalling and reconstructing long and complex sentence structures, can result in overwhelming the capacity of another component, impairing the functioning of systems essential for fluent speech. For example, linguistic processing demands have the potential to have a negative impact on the speech motor system of adults who stutter, thereby leading to increased disfluencies. Kleinow and Smith (2000) showed that adults who stutter responded to increasing linguistic complexity by decreasing the stability of their

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speech motor system. Thus, a number of models of stuttering converge on the account we have given for the interaction of complexity of planning and speech outcomes that we have observed. 4.3. Clinical implications Even though this study did not examine the clinical aspects of stuttering, there are some interesting aspects that might relate to popular fluency-enhancing techniques. For example, the initiation of words and sentences in a very slow manner, and the use of simple sentences as opposed to complex sentences, are common approaches to establishing fluency in the stuttering population (Conture, 2001; Guitar, 2006). Common goals found among these programs involve the targeting of speech rates and the elimination of stuttered disfluencies (Neilson & Andrews, 1993; Onslow, 1996). The adult who stutters slows his speech to a rate so slow that it is practically impossible to stutter. In addition, he usually begins to practice these rates in a hierarchy that goes from less complex to more complex sentences. Then, the speaker increases their rate at a methodical fashion while maintaining fluency. The idea is to stay in the “comfort” zone, or an area that is conducive to fluency. The current study showed that the generation of language involves a processing cost, and this cost is conveyed to the speech motor system, as evidenced by speech initiation time and disfluencies. A logical line of reasoning would suggest that speeding up this process (e.g., generating language, conveying the plan to the motor system, and executing it), would just increase the processing cost to the various neural networks and exacerbate the potential for breakdowns such as disfluencies. In contrast, slowing the process allows for better sentence integration and execution, thereby leading to increased speech fluency. 4.4. Limitations of the current study and future directions Research indicates that sentence structure has an impact on speech initiation time and disfluency in adults who do and do not stutter. These findings need to be integrated into current theories of sentence production and stuttering. However, additional research is needed in determining how processing cost for language interacts with the speech motor control system. A limitation of the current study is the difficult nature in determining whether the source of difficulty originates from a weak psycholinguistic system or a weak speech motor system. Future studies could investigate of subtle linguistic processing skills in which speech motor control is excluded (e.g., comprehension). It is widely assumed that these skills are typical in the stuttering population, but there is very little research literature in this area. Another direction for future research involves the investigation of young children who stutter. Stuttering is a childhood onset disorder that coincides with the emergence and development of sentence structure. Many studies have attempted to make connections between sentence structure and the occurrence or location of stuttering in young children’s spontaneous language. This literature has provided us with mixed results, as sentence length is often confounded with syntactic complexity, making interpretation difficult. Experimental studies in which length is controlled while sentence structure is manipulated may offer a better way of understanding the impact of syntactic complexity on speech motor control in young children who do and do not stutter. 5. Conclusions The present investigation focused on whether sentences of high structural complexity relative to low structural complexity would produce greater production processing costs for fluent adults and adults who stutter, and whether this difference would be exacerbated in the latter group. Results showed that both groups of speakers initiated sentences significantly faster in the low structural complexity condition than in the high structural complexity condition, but adults who stutter were over-all slower in speech initiation than were fluent speakers. A key finding was that high structural complexity led to an increased frequency of disfluencies for all speakers, but that adults who stutter were impacted to a greater degree. Therefore, we conclude that the speech production system of adults who stutter appears particularly vulnerable to higher level demands and processing costs that involve sentence-structure complexity. CONTINUING EDUCATION Effects of Sentence-Structure Complexity on Speech Initiation Time and Disfluency QUESTIONS

1. The first step of sentence construction involves: a. assignment of grammatical functions b. selection of lexical items c. formulation of an abstract idea d. alerting the speech motor system e. gathering conceptual properties

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2. Research has shown that the onset of clauses is associated with: a. critical planning junctures b. decreased normal disfluencies c. decreased stutter-like disfluencies d. decreased speech errors e. decreased processing cost 3. The results of this study indicate that an increase in sentence structure complexity will result in the following for all speakers: a. a decrease in speech initiation time and a decrease in disfluencies b. an increase in speech initiation time and an increase in disfluencies c. an increase in speech initiation time and a decrease in disfluencies d. a decrease in speech initiation time and an increase in disfluencies e. an initial increase in speech initiation time that eventually decreases with practice 4. When mean number of disfluencies and significance levels were analyzed (with Bonferroni correction) for adults who stutter, which sentence type(s) showed a significant difference? a. Subject–object b. Subject–object and subordinate–main c. Clause in NP, passive, and adjunct clause d. Subject–object, subordinate–main, clause in NP, passive, and adjunct clause e. Subject–object, subordinate–main, and clause in NP 5. One implication of the current study is that: a. sentences shown to increase processing cost in a comprehension paradigm do not show the same increase in processing cost when utilized in a production paradigm b. grammatical encoding does not relay a processing cost to the speech motor system c. speech initiation time does not provide a good reflection of processing cost d. the processing cost of organizing a sentence with complex structure taxes the speech motor system Appendix A. Experimental sentences used in Group A Low Syntactic Complexity (No clause in NP) 1. 2. 3. 4. 5. 6.

The strong and agile coyotes hunt in the hills that are next to the lake. The round and shiny doorknob sticks in the cold weather that we get in Edmonton. The short but tedious movie had a sad ending that made everyone cry. The tough and angry lawyer won the case that had been covered in the newspapers. The proud but gifted player left the team that was threatening to trade him. The large but foreign car belongs to the girl who we met at the dance club. High Syntactic Complexity (Relative clause in NP)

7. 8. 9. 10. 11. 12.

The thief who was cornered escaped from the police who were trying to catch him. The plane that was leaving climbed higher into the sky that was clear and blue. The troops that are training marched through the woods that are full of bears. The birds that are frightened flew into the forest that the company wants to chop down. The horse that was training bit the young child who was wearing a pink shirt. The instructor who was useless taught the introductory course that’s now a requirement. Low Syntactic Complexity (Object–Subject Relatives)

13. The girl loved the boy who moved to the southern part of the country. 14. The bird ate the worm that crawled across the ground and into the nest. 15. The plane flew the people who were excited about the upcoming election for governor. High Syntactic Complexity (Subject–Object Relatives) 16. The woman the man liked got the new position of supervisor with the school. 17. The boss the man hated resigned from the job and took some time off. 18. The writer the young student loved had trouble getting funds for his new book.

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Low Syntactic Complexity (Main–Subordinate) 19. The shrewd politician lied because he wanted to win the election for city council. 20. The young boy cried when his mother took the toy out of his room. 21. The angry man yelled when the police arrested him and took him to jail. High Syntactic Complexity (Subordinate–Main) 22. Due to the snowstorm and high gusty winds, the superintendent closed the schools. 23. Because the girl was in charge of the party, the boy called the girl’s home. 24. When the plane landed on the ground, the captain welcomed everyone to New York. Low Syntactic Complexity (Actives) 25. The black and white cat chased the small dog down the busy city street. 26. The large black car hit a yellow school bus late one rainy Friday afternoon. 27. The young mother comforted the child in the waiting room of the doctor’s office. High Syntactic Complexity (Passives) 28. The fast mouse was chased by the clever fox and ran into the woods. 29. The burglar was chased by the state police and sped away from the bank. 30. The student was reprimanded by the teacher and refused to bring the homework. Low Syntactic Complexity (Verb Phrase Complement) 31. The policeman asked the driver to pull over to the side of the road. 32. The mother forced the child to leave the playground in the park and return home. 33. The teacher told the students in the room to sit down and be quiet. High Syntactic Complexity (Adjunct Clause) 34. The teacher lectured the students after returning the assignments that were due last week. 35. The dog ate the food after drinking the water that was in the bowl. 36. The child played with the toy while waiting for his mom to return. Appendix B. Experimental sentences used in Group B Low Syntactic Complexity (No clause in NP) 1. 2. 3. 4. 5. 6.

The smart but crafty thief escaped from the police who were trying to catch him. The small but mighty plane climbed higher into the sky that was clear and blue. The young and fearless troops marched through the woods that are full of bears. The large yet fragile birds flew into the forest that the company wants to chop down. The young but tired horse bit the young child who was wearing a pink shirt. The friendly and kind instructor taught the introductory course that’s now a requirement. High Syntactic Complexity (Relative clause in NP)

7. 8. 9. 10. 11. 12.

The coyotes that are hungry hunt in the hills that are next to the lake. The doorknob that is broken sticks in the cold weather that we get in Edmonton. The movie that was premiering had a sad ending that made everyone cry. The lawyer who was speaking won the case that had been covered in the newspapers. The player who missed practice left the team that was threatening to trade him. The car that was rented belongs to the girl who we met at the dance club. Low Syntactic Complexity (Object–Subject Relatives)

13. The man liked the woman who got the position of supervisor with the school. 14. The man hated the boss who resigned from the job and took time off. 15. The student loved the writer who had trouble getting funds for his new book.

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High Syntactic Complexity (Subject–Object Relatives) 16. The boy the girl loved moved away to the southern part of the country. 17. The worm the bird ate crawled across the wet ground and into the nest. 18. The people the plane flew were excited about the upcoming state election for governer. Low Syntactic Complexity (Main–Subordinate) 19. The superintendent closed the schools due to the snowstorm and high gusty winds. 20. The boy called the girl’s home because the girl was in charge of the party. 21. The captain welcomed everyone to New York when the plane landed on the ground. High Syntactic Complexity (Subordinate–Main) 22. Because he wanted to win the election for city council, the shrewd politician lied. 23. When his mother took the toy out of his room, the young boy cried. 24. When the police arrested him and took him to jail, the angry man yelled. Low Syntactic Complexity (Actives) 25. The clever fox chased the small fast mouse and ran quickly into the woods. 26. The New York City police chased the burglar and sped away from the bank. 27. The angry teacher reprimanded the young boy student and refused to grade the homework. High Syntactic Complexity (Passives) 28. The small dog was chased by the black cat down the busy city street. 29. The school bus was hit by a black car late one rainy Friday afternoon. 30. The child was comforted by the mother in the waiting room of the doctor. Low Syntactic Complexity (Verb Phrase Complement) 31. The teacher told the students to return the assignments on Wednesday of next week. 32. The dog wanted to drink the water from the bowl next to his dish. 33. The young mother hurried to return to the child with the colorful toys. High Syntactic Complexity (Adjunct Clause) 34. The driver cursed the policeman after pulling over to the side of the road. 35. The mother kissed the child before leaving the playground in the park to return home. 36. The students angered the teacher in the room after sitting down and being quiet. References Anderson, J., & Conture, E. (2004). Sentence-structure priming in young children who do and do not stutter. Journal of Speech, Language, and Hearing Research, 47, 552–571. Beattie, G. (1980). The role of language production processes in the organization of behavior in face to face interaction. In B. Butterworth (Ed.), Language production: Vol. 1. Speech and talk. London: Academic. Bernstein, N. (1981). Are there constraints on childhood disfluency? Journal of Fluency Disorders, 6, 341–350. Bever, T., & Townsend, D. (1979). Perceptual mechanisms and formal properties of main and subordinate clauses. In B. Copper, & E. Walker (Eds.), Sentence processing: Psycholinguistic studies presented to Merrill Garrett. Hillsdale, NJ: Lawrence Erlbaum. Bloodstein, O., & Ratner, N. B. (2008). A Handbook on Stuttering. Clifton Park, NY: Delmar Cengage Learning. Bock, K. (1996). Language production: Methods and methodologies. Psychonomic Bulletin & Review, 3, 395–421. Bock, K., & Levelt, W. (1994). Language production: Grammatical encoding. In M. Gernsbacher (Ed.), Handbook of psycholinguistics. Academic Press: San Diego. Boomer, D. (1965). Hesitation and grammatical encoding. Language and Speech, 8, 145–158. Bosshardt, H. (1995). Syntactic complexity, short-term memory, and stuttering. Paper presented at the Annual Convention of the American Speech-LanguageHearing Convention, Orlando, FL. Braun, A. R., Varga, M., Stager, S., Schultz, G., Selbie, S., Maisog, J. M., et al. (1997). Altered patterns of cerebral activity during speech and language production in developmental stuttering: An H2 150 positron emission tomography study. Brain, 120, 761–784. Brown, S. F. (1938). Stuttering with relation to word accent and word position. Journal of Abnormal Social Psychology, 33, 112–120. Brown, S. F. (1945). The loci of stuttering in the speech sequence. Journal of Speech Disorders, 10, 181–192. Butterworth, B. (1980). Some constraints on models of language production. In B. Butterworth (Ed.), Language production: Vol. 1. Speech and talk. London: Academic. Cairns, H., McDaniel, D., Hsu, J., & Rapp, M. (1994). A longitudinal study of principles of control and pronominal reference in child English. Language, 70, 260–288.

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Jim Tsiamtsiouris, Ph.D., CCC-SLP is an Assistant Professor in the Department of Communication Disorders at William Paterson University. His primary research focus is the contribution of psycholinguistic variables on speech fluency.