Elsevier

Journal of Fluency Disorders

Volume 35, Issue 3, September 2010, Pages 216-234
Journal of Fluency Disorders

Relationships among linguistic processing speed, phonological working memory, and attention in children who stutter

https://doi.org/10.1016/j.jfludis.2010.04.003Get rights and content

Abstract

Relatively recently, experimental studies of linguistic processing speed in children who stutter (CWS) have emerged, some of which suggest differences in performance among CWS compared to children who do not stutter (CWNS). What is not yet well understood is the extent to which underlying cognitive skills may impact performance on timed tasks of linguistic performance. The purpose of this study was to explore possible relationships between measures of linguistic processing speed and two aspects of cognition: phonological working memory and attention. Participants were 9 CWS and 14 CWNS between the ages of 3;6 and 5;2. Children participated in a computerized picture naming task (an index of linguistic processing speed) and a nonword repetition task (an index of phonological working memory). Parents completed a temperament behavior questionnaire, from which information about the children's attentional skills was collected. Findings revealed that the groups did not differ from each other on speed of picture naming or attention; however, the CWS performed significantly worse in nonword repetition. In addition, after partialling out the effects of age, (a) for CWS only, there was a significant negative relationship between picture naming speed and nonword repetition; (b) there were no significant relationships for either group between aspects of attention and picture naming speed; and (c) only the CWNS showed a significant relationship between nonword repetition and focused attentional skills. These results underscore the need to consider the underlying skills associated with lexically related aspects of language production when examining the task performances of CWS and CWNS.

Educational objectives: The reader will be able to: (a) summarize findings from previous studies examining the speech and language performance of children who do (CWS) and do not stutter (CWNS); (b) describe findings of previous studies related to nonword repetition and attention in CWS; (c) compare the results of the present study with previous work in this area; and (d) discuss speculations concerning the relationship between linguistic processing speed, phonological working memory, and attention in CWS and CWNS.

Introduction

There has been an increasing interest over the last 20 years in the interaction between language factors and fluency in children who stutter (CWS). Most research in this area has focused on young CWS as they acquire language. As approaches to the measurement of language have become more sophisticated, there has been an increasing emphasis on linguistic processing skills and the measurement of processing speed (e.g., Anderson, 2008, Arnold et al., 2005, Byrd et al., 2007, Hartfield and Conture, 2006, Pellowski and Conture, 2005, Melnick et al., 2003). Studies that incorporate a reaction time component can often detect subtle language processing issues. The underlying skills that enable one to respond quickly to a linguistic prompt are not well understood, however. For instance, theoretically, having a strong vocabulary should aid performance on a naming task, but other factors, including a range of cognitive factors, may play a role as well. Thus, the primary focus of this article is to explore the extent to which two factors in particular, phonological working memory and attentional skills, play a role in linguistic processing speed for CWS and their typically fluent peers. We begin with a discussion of several semantic and phonological processing studies that have most directly informed the present study.

Reaction time studies are employed to go beyond analysis of linguistic accuracy by examining an individual's speed of processing within a particular domain (e.g., phonological, lexical, syntactic). Thus, reaction time is viewed as a sensitive means of examining the efficiency with which a person processes and responds to a language-based stimulus, such as a picture or word. Several recent studies of speech reaction time (SRT) in CWS are relevant to the present study (Anderson and Conture, 2004, Byrd et al., 2007, Hartfield and Conture, 2006, Melnick et al., 2003, Pellowski and Conture, 2005). Anderson (2008) provides a review of these, but to summarize, results of phonological priming SRT studies have been mixed. For example, Melnick et al. (2003) found that, given a phonologically related prime (the initial CV or CCV of the target word), both CWS and CWNS, ages 3–5, had faster SRTs than when they were given no prime or an unrelated prime, and that in both groups, older children had faster SRTs than younger children. There were no significant differences, however, in SRT between the two groups of children. In contrast, Byrd et al. (2007) used SRT to study the effects of incremental priming (i.e., the first sound of the target word) versus holistic priming (i.e., the rest of the word) in CWS and CWNS, ages 3–5. In their cross-sectional study, they found that the CWNS tended to shift from a holistic priming advantage among the younger children in the group to an incremental priming advantage for the older CWNS. The CWS, however, tended to show the fastest SRTs in response to holistic priming regardless of age.

Few studies have examined SRTs for semantically related primes. However, findings from these studies generally suggest that CWS have slower speech reaction times compared to peers (Hartfield and Conture, 2006, Pellowski and Conture, 2005) and that they do not benefit from semantically related primes, whereas CWNS do (Pellowski & Conture). Of interest, Pellowski and Conture found that, for CWNS, faster (shorter) SRTs corresponded to higher receptive vocabulary scores, but for CWS, there was no relationship between vocabulary scores and SRT.

Given these findings, Anderson (2008) hypothesized that perhaps differences between CWS and CWNS lie, to some extent, in the process of mapping semantic representations with phonological representations. She examined this possibility using a picture naming task in which preschool children named pictures of early and late-acquired words in two consecutive stages. Relevant to the present study, she found that even though there was no significant difference between CWS and CWNS in SRT or on standardized measures of vocabulary, CWNS exhibited a significant, positive relationship between SRT and vocabulary (in contrast with Pellowski & Conture, 2005), but CWS did not (consistent with Pellowski & Conture). For CWNS, these findings were interpreted to suggest that perhaps children who had richer vocabularies experienced greater lexical competition and, thus, had slower reaction times than those with poorer vocabularies. However, the fact that CWNS exhibited this association but CWS did not further suggested that some other factor related to lexical processing, such as phonological working memory, may have mediated the observed correlation (or lack thereof). Phonological working memory (as measured through nonword repetition) was targeted as a potential mediating variable, because (a) vocabulary development has been consistently associated with the ability to accurately repeat nonwords (Coady and Evans, 2008, Gathercole, 2006, Gathercole and Baddeley, 1989, Gathercole et al., 1999, Gathercole et al., 1992), and (b) CWS have been shown to be less successful than CWNS in their ability to correctly repeat nonwords, suggesting that they may have difficulties with phonological working memory (see section 1.2.3.; Anderson et al., 2006, Hakim and Bernstein Ratner, 2004; cf. Bakhtiar, Ali, & Sadegh, 2007). Moreover, the ability to respond quickly with the label for a lexical item, it would seem, requires that the item be stored appropriately in memory, to enable efficient retrieval. Indeed, Montgomery and Windsor (2007) found that, for both children with specific language impairment (SLI) and typical peers, response time and nonword repetition were significantly related.

Several authors have theorized about the nature of the relationship between processing speed and memory capacity (e.g., see Montgomery & Windsor, 2007, for a discussion). There is evidence that increases in children's processing speed over development are associated with growth in working memory capacity (e.g., Fry & Hale, 1996; see Fry & Hale, 2000, for a discussion). Fry and Hale's developmental cascade model suggests that, as processing speed increases with age, it enables greater short-term memory capacity,1 which then impacts fluid intelligence (reasoning, problem solving, etc.). In contrast, Luna and colleagues (Luna, Garver, Urban, Lazar, & Sweeney, 2004) suggest that the two abilities develop, for the most part, independently.

In the present study, a follow-up to Anderson (2008), we explore the possibility that in CWS, phonological working memory, as measured through nonword repetition, is associated with processing speed, as measured through SRT. In addition, because lexical processing requires a degree of selective attention to the task, we explore the possibility that attentional abilities are related to processing speed. As will be discussed below, phonological working memory and attention have been theoretically linked in models of working memory.

Baddeley's (2003; also see Baddeley, 1986, Gathercole and Baddeley, 1993) model of phonological working memory provides a reasonable conceptualization of how incoming phonological information is processed/stored in memory. Specifically, according to Baddeley's model, the phonological loop enables short-term storage and rehearsal. Indeed, it seems that most studies of nonword repetition focus interpretation of findings on the phonological loop component of the model. However, as Bajaj (2007) pointed out in his recent review of the working memory literature in relation to stuttering, consideration of the central executive component of Baddeley's model is critical, as well. The central executive is responsible for managing information and regulating attention.

Other models of working memory also describe the role of attention. For example, Cowan (1999) discussed attention-free and attention-focused storage, with attention-focused storage being limited in its capacity. Cowan et al. (2005) emphasizes that the scope of attention, defined as “the capacity of the focus of attention” (p. 49), is important to consider and measure in working memory studies. Moreover, some have argued that working memory tasks are truly measures of attentional control (Engle and Kane, 2004, Redick and Engle, 2006).

Clearly, an individual's ability to attend to the target stimulus is critical if processing of the stimulus is to occur. Thus, in examining children's performance in nonword repetition, it is also important to characterize attentional abilities. The sections that follow provide a review of the literature in the areas of nonword repetition and attention. We begin with a brief review of the literature of children with SLI. This literature has focused on nonword repetition and aspects of attention to a greater extent than the literature related to CWS and can potentially inform work in these areas pertaining to stuttering. Thus, prior work in SLI serves to motivate the present study. Following this discussion, we turn to studies of individuals who stutter.

Interest in the nonword repetition skills of children with SLI perhaps initially stemmed from findings from typically developing children that nonword repetition corresponded to vocabulary development (Gathercole and Baddeley, 1989, Gathercole et al., 1992). Indeed, there is a robust literature focusing on nonword repetition in children with SLI (e.g., Bishop et al., 1996, Conti-Ramsden, 2003, Ellis Weismer et al., 2000, Montgomery and Windsor, 2007, Munson et al., 2005; see Estes, Evans, & Else-Quest, 2007, for a comprehensive list of studies in this area). Estes et al. performed a meta-analysis of studies comparing nonword repetition in children with SLI with that of typical language peers, finding that the effect size of between group differences was large. In addition, relevant to the present study, they found that, of the nonword repetition measures used across studies, the Children's Nonword Repetition Test (CNRep; Gathercole, Willis, Baddeley, & Emslie, 1994) yielded the largest effect sizes, indicating that this measure is the most sensitive of those employed in these earlier studies. Also relevant was the finding that the effect sizes of the differences between groups for 3- and 4-syllable nonwords were large, whereas those for 1- and 2-syllable nonwords were medium. Thus, it appears that, across studies, the longer nonwords distinguished groups the best, as would be expected.

Theorists and researchers have emphasized attention as an important construct to consider, in addition to or as part of understanding phonological working memory (e.g., Baddeley, 2003, Cowan, 1999, Cowan et al., 2005, Engle and Kane, 2004, Redick and Engle, 2006). Within the SLI literature, in particular, there has been a call to look carefully at central executive functioning, which includes aspects of attention, rather than focusing exclusively on phonological working memory. The argument is that, if processing limitations are observed in children with SLI relative to peers, and these limitations extend beyond verbal tasks to spatial processing as well (Hoffman & Gillam, 2004), perhaps central executive functioning should be examined as a broader construct by which to explain processing differences in children with SLI.

Montgomery, Evans, and Gillam (2009) contrasted two types of attention tasks employed within the SLI literature: those that focus on attentional capacity or allocation (e.g., Ellis Weismer et al., 1999, Hoffman and Gillam, 2004, Mainela-Arnold and Evans, 2005, Marton and Schwartz, 2003, Montgomery et al., 2009) and those that focus on sustained or selective attention (e.g., Hanson and Montgomery, 2002, Montgomery et al., 2009, Spaulding et al., 2008, Stevens et al., 2006). An attentional capacity/allocation task might require that an individual hold a word in memory while processing language in some way. For example, the Competing Language Processing Task (Gaulin & Campbell, 1994), requires individuals to listen to sentences of different lengths and judge whether the sentences are true or false, while holding in memory the last word of each sentence in the block of trials. In general, children with SLI perform more poorly than their peers on the “memory” component of these tasks, in particular.

In contrast, a sustained selective attention task might involve listening to linguistic stimuli and responding whenever a target word is heard. For example, the Auditory Continuous Performance Task (Keith, 1993) requires participants to listen to a set of 600 words, responding each time the word dog is heard. In studies that employ procedures of this type, there is conflicting evidence of differences between the performance of children with SLI and their peers. For example, Hanson and Montgomery (2002) found that school-age children with SLI did not differ in their correct/incorrect response rates compared to age-matched peers. However, Spaulding et al. (2008), who developed visual, nonverbal auditory, and linguistic sustained selective attention tasks, found that with background noise, children with SLI performed worse on the linguistic and nonverbal auditory stimuli than peers.

Taken as a whole, it seems that children with SLI do show some differences, relative to peers, in aspects of attention, as well as nonword repetition. Although children who stutter generally are not observed to have clinical language disorders, they have been observed to show subtle differences in language performance (e.g., see Hall, Wagovich, & Bernstein Ratner, 2007, for a discussion). In this paper, we argue that a more complete understanding of memory and attention processes may provide needed insight into performance differences observed in the processing of linguistic stimuli by CWS.

In contrast to the SLI literature, studies of phonological working memory in CWS are considerably fewer. To our knowledge, only three studies have directly examined phonological working memory, measured through nonword repetition with CWS (Anderson et al., 2006, Bakhtiar et al., 2007, Hakim and Bernstein Ratner, 2004). Results have been somewhat conflicting. Hakim and Bernstein Ratner found that CWS, ages 4–8, produced significantly fewer 3-syllable nonwords accurately, compared to age- and gender-matched peers, and they produced significantly more phoneme errors on 3-syllable stimuli than peers. Nonword stimuli of 2, 4, and 5 syllables resulted in no between-groups differences. Similarly, Anderson et al. examined nonword repetition in a younger group of CWS, ages 3–5. They found that the CWS produced significantly fewer 2- and 3-syllable nonwords correctly, with significantly more phoneme errors on 3-syllable nonwords.

In contrast to the aforementioned studies, different results were obtained in a recent study by Bakhtiar et al. (2007). This study examined nonword repetition and the phonological skills of CWS and their peers. Participants were 5–7 years of age and monolingual speakers of Persian. Stimuli were 2- and 3-syllable nonwords. Findings were that the CWS did not differ from peers in the number of phonological errors produced in repeating the nonwords. All three studies were with CWS who did not differ from peers in language scores, and all three incorporated 3-syllable nonwords (on which between-groups differences were found for two of the studies). Thus, there is some methodological similarity across studies. It is possible that the stimuli across studies differed in overall complexity for the children. For example, the Children's Nonword Repetition Test (CNRep; Gathercole et al., 1994), employed by Hakim and Bernstein Ratner (2004) and Anderson et al. (2006), tends to reveal robust differences among children with language impairments and their peers (Estes et al., 2007). We do not know if this is the case for the nonword repetition task developed by Bakhtiar and colleagues although, based on the description of stimuli development, it appears that the nonwords were carefully developed. In sum, the evidence to date does not present a clear picture of the nonword repetition skills of CWS relative to peers.

Most of the fluency disorders literature that focuses on attentional processes has been conducted with adults and has used a dual task paradigm (e.g., Bosshardt, 2002, Bosshardt et al., 2002, Caruso et al., 1994, Smits-Bandstra and De Nil, 2009, Vasic and Wijnen, 2005; see Bosshardt, 2006, Bajaj, 2007, for discussions). For example, Bosshardt et al. asked adults who stutter and typically fluent adults to generate sentences using two target words, while simultaneously making rhyming and category judgments about separate pairs of words. Performance between groups did not differ in the accuracy or speed of rhyme and category decisions. However, the adults who stutter generated sentences with significantly fewer propositions in this dual task condition, compared to the single task condition (sentence generation alone). Typically fluent adults did not show this discrepancy. Findings were interpreted to suggest that perhaps those who stutter, relative to those typically fluent, have greater difficulty directing resources effectively under cognitively demanding conditions. Although this study does not directly speak to the role of attention, it is clear that attention is one of many resources tapped in cognitively complex, dual task experiments.

There has also been an emphasis on automaticity in adults who stutter (e.g., De Nil et al., 2001, Smits-Bandstra and De Nil, 2007, Smits-Bandstra et al., 2006). Achieving automaticity involves directing attentional resources to learning a specific motor skill, so these studies inform our understanding of attentional resources in individuals who stutter, as well. For example, Smits-Bandstra, DeNil, and Rochon employed a single/dual task paradigm with adults who stutter and fluent counterparts. Participants were asked to type sequences of 10 numbers. For the dual task condition, each number sequence changed colors; once the participants typed a number sequence, they were asked whether the same color occurred more than once during the presentation (yes/no). The findings, as pertain to automaticity and attention, were that, while adults who do not stutter showed a steep learning curve in the single task condition (for example, reducing their reaction time with increased practice), adults who stutter demonstrated a shallow learning curve, although overall reaction time did decrease. Of interest, neither group showed substantial learning under dual task conditions (i.e., when attentional skills were taxed). See Smits-Bandstra and De Nil for an overview of this research program.

In contrast to the adult literature, it appears that the literature pertaining to children has focused on attentional skills more indirectly. Studies of temperament have referenced aspects of attention. The temperament of CWS has most often been assessed through parent-report questionnaires (e.g., Anderson et al., 2003, Embrechts et al., 2000, Karrass et al., 2006). Anderson et al. used the Behavioral Style Questionnaire (BSQ; McDevitt & Carey, 1978) to examine aspects of temperament in CWS, ages 3–5, and their peers. They found that the group of CWS obtained higher scores on the attention/persistence dimension of the questionnaire, suggesting greater persistence and lesser attentional flexibility than peers. Similarly, Karrass et al., using the same measure and the same age range of children, found that the CWS were less able to control attention (i.e., less able to shift focus or disengage, as needed).

These findings of reduced attentional flexibility and attentional control in CWS are similar to the findings of Embrechts et al. (2000). They used a different temperament questionnaire, the Children's Behavior Questionnaire (CBQ; Rothbart, Ahadi, Hershey, & Fisher, 2001), and examined a wider age range of 3–8 years. However, despite these differences, they found (as pertains to the present study) that the CWS and CWNS differed significantly in Attentional Focusing, with CWS showing a lesser degree of attentional focus than their peers. Thus, these three temperament studies that utilized parent questionnaires seem to present a similar picture that CWS differ from peers in aspects of attention.

In contrast to the aforementioned studies, Schwenk, Conture, and Walden (2007) examined attention directly in CWS and CWNS, ages 3–5. They compared the number of times the children disengaged from conversational interaction with parents to look at the movement of a mounted video camera in the room. Results revealed that, although the number of camera movements did not differ between groups, the proportion of times the children disengaged from the activity to look at the camera movement was significantly greater for the CWS than the CWNS. Findings were interpreted to suggest that CWS react to a greater extent to environmental stimuli and that they are perhaps less able to regulate responses to changes within their environment. These findings seem to point to potential differences in selective attention.

Careful study of attention processes in CWS is needed (e.g., see Bajaj, 2007, for a discussion of this issue). Although this study is not intended to address that need directly, it provides some insight into the potential correspondence between attention and linguistic processing, to inform future work in this area. As argued above, it is reasonable to hypothesize that attentional characteristics, as well as nonword repetition skills, may be related to linguistic processing tasks, particularly those with a time component, such as SRT. Thus, the purpose of this project was to examine whether nonword repetition and/or attention may relate to children's SRT. Given findings of Anderson (2008) of a positive relationship between the vocabulary measures and SRT in the CWNS but no significant relationship between these variables for the CWS, we hypothesized that, for CWS, nonword repetition and/or attentional characteristics would be associated with SRT performance. Our reasoning was that, if CWS (as a group) show greater variability or weakness in nonword repetition (Anderson et al., 2006, Hakim and Bernstein Ratner, 2004) and attention (Anderson et al., 2003, Embrechts et al., 2000, Karrass et al., 2006, Schwenk et al., 2007), as the literature suggests, perhaps these measures would be more associated with SRT than measures of vocabulary that do not have a time component. The following research questions were posed:

  • (a)

    Does nonword repetition performance relate to SRT in CWS and CWNS?

  • (b)

    Do aspects of attention, in particular, Attentional Focusing, Impulsivity, and Inhibitory Control (Children's Behavior Questionnaire—Short Form, CBQ-SF), Putnam & Rothbart, 2006), relate to SRT in CWS and CWNS?

Section snippets

Participants

Participants were selected from among a pool of children who had participated in two previous studies that examined nonword repetition (Anderson et al., 2006) and repetition priming (Anderson, 2008).2 From this pool of participants, all children who had completed both the nonword repetition and repetition priming studies, and were otherwise typically developing in their speech, language, and hearing (see Section 2.1.2

Results

The primary purpose of this study was to examine the relationships among measures of phonological working memory, linguistic processing speed, and attention for children in the CWS and CWNS groups. However, before examining these results, data were first analyzed for between-group effects in each of the main dependent variables. These analyses were conducted to ensure that the nonword repetition and SRT performance of the children in the current study matched that obtained in Anderson et al.

Discussion

The purpose of the present study was to examine whether two areas of performance, nonword repetition and attention, might be associated with performance on a picture naming SRT task for CWS and CWNS. The study was motivated by the finding of Anderson (2008) that vocabulary scores were associated with SRT in CWNS, but not CWS (cf. Pellowski & Conture, 2005). Based on the literature in phonological working memory and attention, we hypothesized that, for CWS, SRT would be associated with variables

Acknowledgements

This research was supported by a research grant (DC006805) to Indiana University from the National Institute on Deafness and Other Communication Disorders. The authors would like to thank the parents and children who participated in this study, as well as Rebecca Hendricks for her help with data collection. A portion of this research was presented at the annual meeting of the American Speech-Language-Hearing Association, New Orleans, LA, November, 2009. Correspondence concerning this article

Julie Anderson Ph.D., CCC-SLP, is an associate professor at Indiana University. Her research interests include the study of spoken language production and fluency development in young children who do and do not stutter. She is currently an associate editor of the Journal of Speech, Language, and Hearing Research.

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  • Cited by (0)

    Julie Anderson Ph.D., CCC-SLP, is an associate professor at Indiana University. Her research interests include the study of spoken language production and fluency development in young children who do and do not stutter. She is currently an associate editor of the Journal of Speech, Language, and Hearing Research.

    Stacy Wagovich Ph.D., CCC-SLP, is an associate professor at the University of Missouri. Her research interests are in childhood fluency disorders, as well as developmental language disorders. She is currently an associate editor of the Language, Speech, and Hearing in the Schools.

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