Relation of Auditory Attention andComplex Sentence Comprehension in Children with Specific Language Impairment: APreliminary Study

We investigated the relation of two dimensions of attentional functioning (sustained auditory attention and resource capacity/allocation) and complex sentence comprehension of children with specific language impairment (SLI) and a group of typically developing (TD) children matched for age. Twentysix school-age children with SLI and 26 TD peers completed an auditory continuous performance task (ACPT, measure of sustained attention), a concurrent verbal processing-storage task (measure of resource capacity/allocation), and a picture pointing comprehension task. Correlation analyses were run to determine the association between the measures of attention and sentence comprehension. The SLI group performed more poorly than the TD group across all tasks. For the SLI group, even after removing the effects of age, ACPT score and performance on the concurrent processing-storage task still significantly correlated with complex sentence comprehension. Sustained attention also correlated with simple sentence comprehension. Neither attention variable correlated with sentence comprehension in the TD children. For children with SLI, the comprehension of complex grammar appears to involve significant use of sustained attention and resource capacity/allocation. Even simple sentence comprehension requires significant auditory vigilance. In the case of TD children, neither complex nor simple sentence comprehension appears to invoke significant attentional involvement. Children with specific language impairment (SLI) have special difficulty comprehending complex grammar (Bishop, Bright, James, Bishop, & van der Lely, 2000; Montgomery & Evans, in press; Norbury, Bishop, & Briscoe, 2002; van der Lely, 1996, 1998; van der Lely & Stollwerck, 1997). Many of these same children © 2008 Cambridge University Press 0142-7164/08 $15.00 Applied Psycholinguistics 30:1 124 Montgomery et al.: Attention and complex sentence comprehension also evidence a wide array of limitations in other cognitive abilities such as in the areas of phonological memory capacity (Dollaghan & Campbell, 1998; Gathercole & Baddeley, 1990; Marton & Schwartz, 2003; Montgomery, 1995, 2004) and speed of processing (Leonard et al., 2007; Miller, Kail, Leonard, & Tomblin, 2001; Montgomery, 2002, 2005; Windsor & Hwang, 1999a). It also has been suggested that, relative to age peers, children with SLI have attentional limitations, including poorer selective attention (e.g., Stevens, Sander, & Neville, 2006), sustained attention (e.g., Helzer, Champlin, & Gillam, 1996; Montgomery, 2005, 2008), and reduced attentional resource capacity/allocation (Ellis Weismer, Evans, & Hesketh, 1999; Hoffman & Gillam, 2002; Marton & Schwartz, 2003; Montgomery, 2000a, 2000b). However, the nature of the relation between these children’s complex sentence comprehension deficits and their apparent attention difficulties is unclear. The aim of the present study was to address this issue. SENTENCE COMPREHENSION DEFICITS IN SLI As a group, children with SLI show much greater difficulty processing and comprehending complex sentences than their age-matched peers (e.g., Bishop et al., 2000; Montgomery & Evans, in press; Norbury et al., 2002; van der Lely, 1996, 1998; van der Lely & Stollwerck, 1997). In these studies, children with SLI and typically developing (TD) children listened to complex sentences such passives (e.g., The boy was kissed by the girl) and pronominals (e.g., Mowgli says that Baloo Bear is touching him) as well as simple active sentences. After each sentence the child selected from an array of pictures that one best matching the sentence. Across all of the studies, children with SLI, relative to age peers, consistently showed poorer comprehension of the complex sentences but not the simple sentences. It has also been shown that, relative to age mates, children with SLI have marked difficulty in understanding sentences containing center-embedded relative clauses, even when such sentences conform to canonical word order (Curtiss & Tallal, 1991; Montgomery, 1995, 2000a, 2000b, 2004). For instance, in the Montgomery studies children with SLI and TD age mates listened to simple sentences (e.g., The dirty boy climbed the tall tree) and semantically reversible complex sentences containing either one relative clause (e.g., The girl laughing is touching the boy) or two relative clauses (e.g., The little boy standing is hugging the little girl sitting). The simple and complex sentences were crafted into two sentence length conditions, one corresponding to a set of short-version sentences containing simple sentences and complex sentences and the other corresponding to a set of long-version sentences matched to the shorter sentences for semantic content and syntactic structure. Thus, the only difference between the shortand long-version sentences is that the longer sentences contained extra (nonessential) verbiage. The aim of the studies was to follow up the Curtiss and Tallal study by assessing the (a) effect of sentence length (not sentence structure) on children’s comprehension and (b) relation between short-term memory (STM) and sentence comprehension. From these studies, it was shown that the children with SLI had significantly greater trouble comprehending the longer sentences than the short sentences, relative both to the TD children and to themselves. However, given the nature of the analyses (i.e., analyses commingled sentence complexity and length) Applied Psycholinguistics 30:1 125 Montgomery et al.: Attention and complex sentence comprehension it was unclear what specific effect complexity had on the comprehension of the children with SLI separate from length. However, inspection of the children’s response patterns revealed that the children with SLI had a strong tendency to miscomprehend the complex sentences but not the simple sentences, regardless of sentence length. In the case of passive and pronominal sentences, van der Lely and colleagues (van der Lely, 1996, 1998, 2005; van der Lely & Stollwerck, 1997) proposed that the poorer comprehension of these structures by children with SLI is attributable to a deficit in the syntactic system. Specifically, these investigators suggest that these children’s core deficit is in the representations and/or mechanisms responsible for building hierarchical grammatical structures, that is, computing syntactic dependencies (particularly long distance ones) between different sentence elements. Framed within Chomsky’s Minimalist Program (1995), it is, moreover, proposed that children with SLI treat the syntactic operation Move, as optional. By contrast, in TD children the Move operation functions obligatorily. There is, however, another explanation for these children’s comprehension problems. Reduced general processing capacity may well interfere with these children’s comprehension of a range of complex sentence structures. PROCESSING CAPACITY DEFICITS AND SENTENCE COMPREHENSION IN SLI Phonological STM (PSTM) and comprehension One prominent and well-documented processing capacity deficit that children with SLI exhibit is in the area of PSTM capacity. Many children with SLI have less ability to store as much verbal information at any given moment as TD children (Dollaghan & Campbell, 1998; Gathercole & Baddeley, 1990; Montgomery, 1995, 2000a). The PSTM capacity of children with SLI has been estimated using a variety of recall tasks, including digit span or word span (Archibald & Gathercole, 2007) and nonword repetition (Dollaghan & Campbell, 1998; Ellis Weismer et al., 2000; Gathercole & Baddeley, 1990; Montgomery, 2000a). The consistent pattern across studies is that children with SLI demonstrate significantly reduced recall compared with their same-age TD peers. It has been argued that a limitation in PSTM capacity, under certain circumstances, interferes with the language comprehension of these children (Montgomery, 2002). Norbury et al. (2002), for example, provide indirect evidence for this claim. They showed that a deficit in PSTM (indexed by nonsense word repetition) significantly correlated with the poorer comprehension of passive and pronominal sentences in children with SLI. Similarly, reduced PSTM capacity may well help explain, at least in part, the difficulty children with SLI have comprehending complex sentences containing doubleand single-embedded relative clause sentences (e.g., Montgomery, 1995). In three studies by Montgomery (2000a, 2000b, 2004) children listened to simple and complex sentences (in both long and short versions of each other), with sentence length being the key variable of interest. The children also completed a nonword repetition task. Two common findings emerged from these studies. First, regardless of sentence length, the Applied Psycholinguistics 30:1 126 Montgomery et al.: Attention and complex sentence comprehension children with SLI showed a very strong tendency to miscomprehend the complex sentences but not the simple ones. Second, relative to TD children, the children with SLI performed significantly worse on the nonword repetition task, suggesting they had a marked PSTM capacity deficit. Correlation analyses showed no significant relation between PSTM and the comprehension of the long sentences (Montgomery, 2000a, 2000b, 2004) but these findings may have been because of a lack of power. Given the co-occurrence of memory problems and difficulties with complex sentence comprehension, it is possible that some sort of information processing limitation of the children with SLI interfered with their complex sentence comprehension. Auditory/verbal attention Some theoretical background. It has been argued by some cognitive researchers (e.g., Baddeley, 1999; Cowan, 1999; Guttentag, 1989; Posner, 1995; Shiffrin & Schneider, 1977) that attention plays a critical role in much of cognitive processing, including language processing. Although current theories view attention as a complex multidimensional construct (e.g., Baddely, 1999; Cooley & Morris, 1990; Cowan, 1999; Mirsky, Anthony, Duncan, Alhearn, & Kellam, 1991), there is no single dominant theory. From a neuropsychological perspective (Mirsky et al., 1991) attention includes several experimentally identifiable dimensions, including sustained attention. Sustained attention refers to the ability to maintain attentional alertness (arousal) over time in an effort to identify/select a specific stimulus (target) in the midst of other (distracting) stimuli in a continuous flow of incoming information. Another prominent view of attention is that the attentional system comprises a limited amount of resources/capacity or “mental energy” (e.g., Baddeley, 1999, 2002) that can be devoted in whole or in part to some cognitive activity. Closely related to capacity is resource allocation. Allocation refers to one’s ability to split one’s mental resources in a flexible way while carrying out a cognitive activity such as sentence processing/comprehension. For example, someone who is listening to a speaker in a noisy room might allocate some of his/her mental resources to syntactic and semantic operations while at the same time he/she allocates considerably more resources to phonological operations to ensure accurate lexical processing (and word recognition). Experimental studies of adult language processing suggest that attention has an important functional role in language processing/comprehension. Neuroimagaing data from a study by Lockwood, Murphy, and Khalk (1997), for example, indicate that neural mechanisms associated with sustained attention are activated in adults during reading comprehension, as well as during grammaticality judgment tasks. With respect to resource capacity/allocation, perhaps the best-known behavioral evidence comes from the work of Just and Carpenter and colleagues (e.g., Just & Carpenter, 1992; King & Just, 1991) as well as others (e.g., Chen, Gibson, & Wolf, 2005; Roberts & Gibson, 2002). The results of these studies suggest that the comprehension of complex sentence structures invites the controlled and flexible use of listeners’ attentional resources. Investigators can approach the study of language processing from a broad working memory perspective or from the perspective that attentional resource Applied Psycholinguistics 30:1 127 Montgomery et al.: Attention and complex sentence comprehension capacity/allocation is a submechanism of working memory. In the present study, we are conceptualizing attentional resource capacity/allocation to be a submechanism of the broader construct working memory. In either case, there is at least one important structural and functional similarity between the construct of working memory and the notion of attentional resource capacity/allocation. Both perspectives entail the notion that listeners are endowed with a finite pool of activation (i.e., mental energy) that can be allocated to both verbal processing and storage, with the allocation of resources being dictated by the demands of the comprehension task. Listeners’ working memory or attentional resource capacity/allocation capacity is often estimated using concurrent information processing-storage tasks (i.e., listening span task, counting span task) in which listeners must perform some kind of cognitive processing task such as performing math problems or comprehending sentences while simultaneously remembering the number of dots presented in an array or a list of words. Research has shown that adults’ performance on such concurrent processing-storage tasks correlates significantly with their processing/comprehension of complex sentences. Moreover, it has been shown that increases in syntactic complexity call for greater amounts and more flexible use of a listener’s attentional resources (or working memory capacity). Auditory/verbal attention limitations in SLI. Within the SLI literature, research into the attentional abilities of children with SLI, particularly sustained attention, is limited. There are, however, some neurophysiological data suggesting that children with SLI have problems with selective auditory attention, especially at the earliest stages of sensory processing (e.g., Stevens et al., 2006; Uwer, Albrecht, & von Suchodoletz, 2002). There is also some anecdotal evidence that these children have difficulty maintaining auditory attention and that this difficulty may relate to their poorer performances on various language-related tasks. Helzer et al. (1996), for example, assessed the perceptual processing of children with SLI and TD children using gap detection tasks. The children with SLI, although showing similar thresholds overall to the TD children, required significantly more trials to reach criterion than their age-matched peers. These researchers suggested that poor sustained attention was a likely explanation of the “slower” learning of the children with SLI. Other investigators (e.g., Stark & Heinz, 1996) have reported similar results of children with SLI being less efficient to learn the acoustic cues that differentiate phoneme contrasts, with the implication being that poor attention could be a contributing factor. More recently, Spaulding, Plante, and Vance (2008) provided more direct behavioral evidence suggesting that preschoolers with SLI have significantly greater difficulty than age peers sustaining their auditory attention, especially under cognitively demanding conditions. Of interest, these authors found no evidence that the sustained attention problems of the children with SLI crossed over into the visual modality. In contrast to the nearly absent literature exploring the auditory vigilance of children with SLI there is a developing literature on these children’s attentional capacity/allocation (e.g., Ellis Weismer, Evans, & Hesketh, 1999; Hoffman & Gillam, 2004; Mainela-Arnold & Evans, 2005; Marton & Schwartz, 2003; Montgomery, 2000a). Children in all of these studies completed concurrent verbal processing and storage tasks in which they engaged in verbal processing while at Applied Psycholinguistics 30:1 128 Montgomery et al.: Attention and complex sentence comprehension the same time remembering/recalling sets of words. The results of these studies have consistently shown that children with SLI typically show similar processing (i.e., comprehension) to TD children but significantly poorer word recall. For instance, results from Ellis Weismer et al. (1999) and Mainela-Arnold and Evans (2005), both of whom used the competing language processing task (CLPT; Gaulin & Campbell, 1994), showed that children with SLI and TD children had comparable comprehension but the children with SLI yielded significantly lower word recall, particularly as the number of to be recalled words increased. Montgomery (2000a, 2000b) used a three-tier word recall task to assess the attentional resource capacity/allocation of children with SLI and TD children. The children were asked to recall as many familiar nouns (e.g., tree, cat, seed) as they could under three different processing load conditions. One condition was a simple span task requiring free recall. A second (single-load) condition asked children to recall word lists according to the “physical size” of the word referents beginning with the word referring to the smallest referent and ending with the one referring to the largest referent. In the third (dual-load) condition, children were asked to arrange the words (a) into two semantic categories and then (b) according to the size of the word referents within each category as in the single-load condition. For example, if a child were given the word list bike, nut, car, tree, plane, the proper response would be bike, car, plane//nut, tree. Thus, this condition not only required the children to maintain accurate verbal storage but also to perform two mental operations. Results were clear cut in both studies. The two groups yielded similar word span in both the simple and single-load conditions. The groups’ similar simple span were taken to suggest that the SLI and TD groups had overall comparable STM capacity in the absence of any processing demands. Similarly, the groups’ comparable single-load performance implied that the children with SLI were comparable to TD children in allocating their mental resources to both STM and semantic processing (i.e., mental operation associated with rearranging the words by referent size). However, it was performance in the dual-load condition that discriminated the groups, with the children with SLI performing significantly worse (i.e., recalling fewer words). The poorer performance of the SLI group was interpreted to mean that under high-load processing conditions (e.g., completing two mental operations) the verbal storage of these children suffers. To help explain why the SLI group attained a lower dual-load word span than the TD children an error analysis was performed focusing on whether the children had difficulty establishing the semantic categories, rearranging the words according to referent size, or both. Inspection of the error patterns revealed that although the children with SLI were able to establish two semantic categories (albeit one category may have contained just one item) their greatest difficulty related to properly ordering the words by referent size and/or remembering all of the words within each category. Thus, the children had the ability to perform the semantic categorization part of the task but lacked sufficient resources to complete the second mental operation before some of the items faded from memory. Taken together, the results across all of the SLI studies to date suggest that the difference between children with SLI and TD children is not in the ability to allocate mental resources. Rather, children with SLI appear to have less Applied Psycholinguistics 30:1 129 Montgomery et al.: Attention and complex sentence comprehension overall attentional resources available to perform such concurrent processingstorage tasks. Relation between attention and sentence comprehension in SLI. The potential influence of resource capacity/allocation on the sentence comprehension of children with SLI has received some research attention, but the extant findings are mixed. Ellis Weismer et al. (1999), for instance, reported a positive relation between the CLPT (word recall) and score on a standardized sentence comprehension test (including simple and complex structures) for TD children but not in children with SLI. Although using different resource capacity/allocation and sentence comprehension tasks, Montgomery (2000a, 2000b) also reported no association between resource capacity/allocation and sentence comprehension. However, given that both simple and complex sentences were commingled in the analyses any potential association between attention and at least complex sentence comprehension may have been obscured. Ellis Weismer and Thordardottir (2002) did, however, show that, after accounting for nonverbal IQ, the most unique variance in standardized sentence comprehension score of children with SLI and TD children was accounted for by resource capacity/allocation. No research has examined what role sustained attention might play in the sentence comprehension of children with SLI. Results of a real-time sentence processing study by Montgomery (2008), however, might provide a clue. In this study, 6to 10-year-old children with SLI and TD children completed a continuous performance task, the dual-load word recall task described above, and a conventional word recognition reaction time (RT) task. The vigilance task was the same one used in the present study in which children were asked to complete an 11-min task in which they responded to hearing a target word (dog) as it appeared amidst a stream of nontarget items. The word-monitoring task (which comprised only simple sentences) required children to make a timed response immediately upon recognizing a sentence-embedded target word. Results showed that both sustained attention and resource capacity/allocation significantly correlated with sentence processing (indexed by word recognition RT) but only for the children with SLI. Results were interpreted to mean that simple grammar is not yet processed “automatically” by children with SLI but it is by TD children. AIM AND PREDICTIONS OF THE PRESENT STUDY Few studies have examined the intersection of the attentional and language processing systems in children with SLI. The results of one study (Montgomery, in press) suggest that the interplay between the systems may be different in children with SLI and TD children, at least with respect to online sentence processing. The purpose of the present study was to investigate whether sustained attention and resource capacity/allocation are related to the offline complex sentence comprehension of children with SLI and TD children. Relative to TD children, the children with SLI should show (a) poorer sustained auditory attention on an auditory continuous performance task (e.g., Montgomery, 2008) and (b) reduced attentional resource capacity/allocation (Ellis Weismer et al., 1999; Mainela-Arnold & Evans, 2005; Montgomery, 2000a) on a Applied Psycholinguistics 30:1 130 Montgomery et al.: Attention and complex sentence comprehension two-tier word recall task. It was also predicted that for both groups both aspects of attention should significantly correlate with complex sentence comprehension given the overall cognitive demands of such an offline task and the results of the adult language processing literature showing sustained attention is involved in reading comprehension (Lockwood et al., 1997) and an association between resource capacity/allocation and complex sentence comprehension (e.g., Chen et al., 2005; Just & Carpenter, 1992; Roberts & Gibson, 2002). Successful comprehension should require the children’s sustained attention and attentional resource capacity/allocation because they must maintain their attention and allocate their resources through the course of processing the sentence as they (a) generate an appropriate linguistic representation of the input, (b) scan and visually process each picture, (c) generate a corresponding linguistic representation of each of the pictures, and (d) select the one picture that best matches the input sentence. With respect to simple sentences, we predicted no correlation should emerge between attention and comprehension for the TD children. This prediction is based on the fact that the sentences are well within the linguistic competence of the children (e.g., DeVilliers & DeVilliers, 1973; Dick, Wulfeck, Krupa-Kwiatkowski, & Bates, 2004). For the children with SLI, even though the sentences are within their linguistic grasp a significant correlation should emerge between both aspects of attention and comprehension given that the offline comprehension task entails a number of attention-demanding mental operations (e.g., Montgomery, in press).