Working Memory Functioning in Children With Learning Disorders and Specific Language Impairment

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1 Top Lang Disorders Vol. 33, No. 4, pp Copyright c 2013 Wolters Kluwer Health Lippincott Williams & Wilkins Working Memory Functioning in Children With Learning Disorders and Specific Language Impairment Kirsten Schuchardt, Ann-Katrin Bockmann, Galina Bornemann, and Claudia Maehler Purpose: On the basis of Baddeley s working memory model (1986), we examined working memory functioning in children with learning disorders with and without specific language impairment (SLI). We pursued the question whether children with learning disorders exhibit similar working memory deficits as children with additional SLI. Method: In separate analyses, we compared the following groups of children: (1) 30 children with dyslexia (DYS) and 16 children with DYS receiving special language education and (2) 19 children with combined disorder of scholastic skills (CDSS) and 18 children with CDSS receiving special language education. A control group of 30 typically developing children was included in each comparison. All of the children receiving special language education met criteria for SLI. To assess the 3 subcomponents of working memory (phonological loop, visual spatial sketchpad, central executive), the children worked individually on an extensive test battery. Results: We found deficits in the phonological loop and central executive functioning for children with dyslexia (and CDSS) as well as for children with additional SLI. Deficits in phonological functioning were broader and more profound for children with SLI. Deficits in visual spatial sketchpad could only be found for children with CDSS without SLI. Conclusions: Children with isolated learning disorder and children with additional SLI demonstrate similarities and differences in working memory functioning. These findings support our hypothesis that underlying working memory deficits for the different disorders partly overlap but also are distinct and partly distinguish between certain disorders. Key words: combined disorder of scholastic skills, dyslexia, learning disorder, specific language impairment, working memory LEARNING DISORDERS REPRESENT one of the most frequent causes for school failure. Children with specific learning disorders such as dyslexia and dyscalculia show general Author Affiliations: Department of Diagnostic and Educational Psychology (Drs Schuchardt, Bockmann, and Maehler and Ms Bornemann), University of Hildesheim, Hildesheim, Germany. The authors have indicated that they have no financial and no nonfinancial relationships to disclose. Corresponding Author: Kirsten Schuchardt, PhD, Department of Diagnostic and Educational Psychology, University of Hildesheim, Marienburger Platz 22, 31141, Hildesheim, Germany ([email protected]). DOI: /01.TLD impairments in acquiring the cultural techniques of reading, spelling, and calculating. Dyslexia describes specific deficits in reading acquisition (often combined with spelling disorder), and dyscalculia is characterized by deficits in arithmetic skills. The exact definitions and diagnostic criteria of learning disorders differ widely, but some sources are used commonly across the world. International Classification of Diseases, Tenth Revision (ICD-10, 2011) by the World Health Organization defines internationally accepted diagnostic criteria. Here, learning disorders are described as poor performance in reading, spelling, and calculating, respectively, that must be significantly lower than expected with regard to age, intelligence, and schooling.

2 Working Memory Functioning in Children With Learning Disorders and SLI 299 It is not unusual that learning disorders occur together with specific language impairment (SLI), which is characterized by serious qualitative and quantitative deficits in productive and/or receptive language proficiency. The ICD-10 (Code F80) defines specific developmental disorders of speech and language as disorders in which normal patterns of language acquisition are disturbed from the early stages of development. It specifies further that the conditions are not directly attributable to neurological or speech mechanism abnormalities, sensory impairments, mental retardation, or environmental factors. Specific developmental disorders of speech and language are often followed by associated problems, such as difficulties in reading and spelling. Approximately 25% 75% of all children with language impairment develop reading difficulties (Catts, Adlof, Hogan, & Ellis Weismer, 2005; McArthur, Hogben, Edwards, Heath & Mengler, 2000; Tomblin, Zhang, Buckwalter, & Catts, 2000). On the contrary, according to Catts et al. (2005), every fifth child with dyslexia shows a history of difficulties in language acquisition. If language disorders persist until school age, the rate of children demonstrating specific reading disability climbs to 50% (McArthur et al., 2000). Children with SLI also can experience difficulties. These difficulties can emerge prior to formal schooling and persist during the school-age years (Cowan, Donlan, Newton, & Lloyd, 2005; Donlan, Cowan, Newton, & Lloyd, 2007; Eisenmajer, Ross, & Pratt, 2005; Fazio, 1994, 1996, 1999). Given this high comorbidity rate, recent research has started to investigate the commonalities and shared causal factors of learning disorders and SLI. Within recent years, one question has been addressed in particular: Are SLI and learning disabilities distinct disorders with different causal factors or are they various manifestations of the same underlying cognitive factors (Baird, Slonims, Simonoff, & Dworzynski, 2011; Catts et al., 2005; de Bree, Wijnen, & Gerrits, 2010)? WORKING MEMORY As possible causal factors underlying SLI and learning disorders, researchers have identified deficits in working memory and diverse aspects of phonological information processing, such as phonological awareness (Catts et al., 2005; Eisenmajer, et al., 2005; Nithart et al., 2009). Although various models of working memory have been developed, the model by Baddeley (1986) has proved a particularly useful theoretical tool in numerous studies in this area. The model distinguishes between different components of working memory, with the modality-free central executive acting as a kind of supervisory system that serves to control and regulate the cognitive processes occurring in its two limitedcapacity slave systems, the phonological loop and the visual spatial sketchpad. Further functions of the central executive that have since been identified by Baddeley (1996) include coordinating the slave systems, focusing and switching attention, and retrieving representations from long-term memory. In contrast, Baddeley s (1986, 1996) two slave systems perform modality-specific operations. Verbal and auditory information is stored temporarily and processed in the phonological loop. Whereas verbal or auditory information enters the phonological store directly, visual information has to be translated into phonological code before it can do so. Two components of the phonological loop are distinguished: the phonological store and the subvocal rehearsal process. The visual spatial sketchpad is concerned with remembering and processing visual and spatial information; it comprises a visual cache for static visual information and an inner scribe for dynamic spatial information (Logie, 1995; Pickering, Gathercole, Hall, & Lloyd, 2001). Later, Baddeley (2000) added a fourth component to the working memory model, the episodic buffer, for linking long-term memory and integrating information from all of the other systems into a unified experience. To date, however, research on working memory

3 300 TOPICS IN LANGUAGE DISORDERS/OCTOBER DECEMBER 2013 has mostly focused on the three original subcomponents, probably because it turned out to be difficult to create valid tasks measuring the functioning of the episodic buffer. WORKING MEMORY AND LEARNING DISORDERS There is considerable evidence that children with dyslexia have deficits in phonological processing and storage (Schuchardt, Maehler, & Hasselhorn, 2008; Vellutino, Fletcher, Snowling, & Scanlon, 2004). Children have been found to exhibit a reduced memory span for acoustically presented words, numbers, and nonwords. Numerous studies on dyslexia and accompanying deficits in complex abilities such as text comprehension also detect deficits in central-executive working memory functioning (Landerl, Bevan & Butterworth, 2004; Schuchardt et al., 2008; Siegel & Ryan, 1989). In contrast, hardly any reliable correlations between visual spatial sketchpad functioning and dyslexia could be found (O Shaughnessy & Swanson, 1998; Schuchardt et al., 2008). Researchers studying working memory functioning in children with dyscalculia have reported deficits in the visual spatial sketchpad (Schuchardt et al., 2008), whereas mixed results have been reported for the phonological loop and central executive. Some studies show them not to be impaired (McLean & Hitch, 1999; Schuchardt et al., 2008), whereas others do report deficits in the phonological loop or central executive (McLean & Hitch, 1999; Swanson & Sachse-Lee, 2001). Children with a combined disorder of scholastic skills (CDSS; a term used in Germany on the basis of the ICD-10 to describe learning difficulties in reading and writing as well as mathematics) have been found to have severe deficits in all three working memory components (Maehler & Schuchardt, 2009; Schuchardt et al., 2008). Some of this research (Maehler & Schuchardt, 2009) has shown similar performance patterns between children with intelligence below average and children with CDSS, who, by definition, have average intelligence. Deficits in working memory functioning have been investigated extensively also for children with SLI. Children with SLI display severe deficits in phonological loop functioning (Archibald & Gathercole, 2006b, 2007; Marton & Schwartz, 2003). Results concerning visual working memory are inconsistent. Although some studies did not find any impairment of visual spatial sketchpad in children with SLI (e.g., Archibald & Gathercole, 2006a; Riccio, Cash, & Cohen, 2007), others have reported significantly lower scores for children with SLI on tasks assessing the visual spatial sketchpad than those for typically developing children (e.g., Hick, Botting, & Conti- Ramsden, 2005; Hoffman & Gillam, 2004). In addition to these phonological and visual spatial difficulties exhibited by children with SLI, deficits in central executive processing are evident (Archibald & Gathercole, 2006b; Marton & Schwartz, 2003; Montgomery & Evans, 2009). These deficits in central executive are not confined to phonological material, they also occur with visual spatial material. This lends support to the hypothesis that children with SLI demonstrate a broader impairment of central-executive functioning, which is not restricted to phonological information processing. In summary, it can be stated that specific patterns in working memory functioning have been detected both for learning disorders and SLI and that some similarities in deficit profiles are evident. Nevertheless, only a few studies have directly compared working memory profiles in children with both specific and comorbid learning deficits although such comparisons are crucial to understanding the potential common or distinct cognitive impairments associated with different learning profiles. Catts et al. (2005) examined children with dyslexia, SLI, and combined SLI and dyslexia. Only children with reading difficulties (with or without SLI) performed poorly on phonological awareness and phonological working memory tasks, whereas the SLI and control groups did not. Catts et al. concluded that SLI and dyslexia are distinct disorders with overlapping difficulties in basic

4 Working Memory Functioning in Children With Learning Disorders and SLI 301 cognitive functioning. However, Catts et al. relied on a preschool SLI diagnosis and did not examine whether the children with SLI still met the criteria for SLI at school age. Therefore, it is an open question whether schoolaged children with a current diagnosis of SLI, dyslexia, or both SLI and dyslexia will show overlapping or different patterns of working memory functioning. We also could find no studies on children with SLI and comorbid severe learning disorder in reading, spelling, and arithmetic skills (CDSS). We, therefore, wanted to investigate whether children with SLI and comorbid CDSS exhibit working memory impairments that are similar in profiles and as severe as those observed for children with CDSS but without SLI. The purpose of this research was to examine whether children with persisting language impairment and children with learning disorders in either reading only or across scholastic domains exhibit the same deficits in working memory. We hypothesized that deficits in the same working memory components would be suggestive of a common underlying cognitive impairment whereas unique deficits would correspond to different underlying impairments. In our study, children with learning disorders and children with combined learning disorders and SLI underwent an extensive working memory test battery with tasks on all subcomponents with the exception of the episodic buffer. We then compared the patterns of the following groups of children: (1) children with isolated dyslexia and children with comorbid SLI and dyslexia and (2) children with CDSS (i.e., dyslexia and dyscalculia) and children with SLI and CDSS, and a control group of typically developing children. METHODS Participants Five groups of children (second- to fourthgrade students) participated in the study: (1) children with dyslexia but not referred for special language education (SLE) (DYS; n = 30); (2) children with dyslexia and referred for SLE (SLI + DYS; n = 16); (3) children with CDSS but not referred for SLE (CDSS; n = 19); (4) children with CDSS and referred for SLE (SLI + CDSS; n = 18); and (5) a control group of typically developing children matched for chronological age (C; n = 30). The two groups of children with learning disorders (DYS and CDSS) were recruited from the counseling center for children with learning disabilities, which is part of a university programinacityofgermany.allofthemattended regular primary schools; due to learning problems, they voluntarily attended the diagnostic procedures described later and received the diagnosis DYS or CDSS. The two groups of children referred for SLE (SLI + DYS and SLI + CDSS) attended a school for SLE. Their SLI-diagnoses were present before they participated in the study. Being referred for SLE and attending a special school reveals severe problems of language development in the two SLI groups. The typically developing children in the control group were second to fourth graders from a public elementary school. Only native German-speaking children were included in the study sample. No information on socioeconomic status of the families was available. Diagnostic classification The two groups of children with SLI (SLI + DYS and SLI + CDSS, who all attended a school for SLE) were tested for language development and intelligence before they were referred to special education and before they took part in the study. Because of time restrictions, we accepted their intelligence testing but we confirmed their language deficits. The two groups with learning disorders (DYS and CDSS) had not been tested before and received their diagnosis through our testing. We did not examine language performance in these groups, because there was no indication for these tests in the context of the counseling center (no language problems reported by parents or teachers). Of course, one

5 302 TOPICS IN LANGUAGE DISORDERS/OCTOBER DECEMBER 2013 might argue that language impairment in children with learning disorders might be more subtle and harder to identify but yet, observable through their lower school achievement. Unfortunately, we cannot rule out this possibility because, due to the routine procedure within the counseling center and time restrictions, we did not apply any direct measures for language development to these children. However, given the severe language impairment of the children receiving SLE, we dare to rely on a significant difference in language development between the learning disorder and SLI groups. All children were screened with standardized tests for intellectual ability, spelling, reading, and arithmetic. Different German intelligence tests had been used for the children with SLI before (CFT-1, Cattell, Weiss, & Osterland, 1980; IDS, Grob, Meyer, & Hagemann-von Arx, 2009; K-ABC, Melchers & Preuss, 2001; SON-R, Tellegen, Winkel, & Laros, 2003), in the counseling center the K-ABC (Melchers & Preuss, 2001) was used. For our study, we relied on the measures for nonverbal intelligence in the different intelligence tests that captured a similar concept of logical reasoning. Mathematical skills were assessed using standardized German mathematical achievement tests for second, third, and fourth graders (DEMAT 2+, Krajewski, Liehm, & Schneider, 2004; DEMAT 3+, Roick, Gölitz, & Hasselhorn, 2004; DEMAT 4, Gölitz, Roick, & Hasselhorn, 2006). These multicomponent tests include computation problems, word problems, and geometry problems. Spelling abilities were assessed by the Weingartener spelling tests for second and third graders (WRT 2+, Birkel, 1994a; WRT 3+, Birkel, 1994b) and the Westermann spelling test for fourth graders (WRT 4/5, Rathenow, 1980). In both of these standardized German achievement tests, children insert dictated words into given sentences. Reading speed abilities were classified on the basis of scores on two subtests of the Salzburg reading test (SLT; Landerl, Wimmer, & Moser, 1997): the word reading subtest Textlesen (short or long version, depending on grade level) and the nonword reading subtest Wortunähnliche Pseudowörter. Based on the test battery described previously, the operational criteria for the learning disorder subgroups in this study were as follows: (a) IQ 80; (b) below-average reading, spelling, and/or arithmetic scores (T < 40 [i.e., T scores: mean of 50 and SD of 10] or percentile < 16); and (c) a critical discrepancy of at least 1.2 SDs between IQ and overall performance on the standardized tests of school achievement (DYS groups: discrepancy between tests of reading and spelling and intelligence; CDSS groups: discrepancy between tests of reading, spelling, and arithmetic compared with intelligence). The criteria for the control group of typically developing children were normal intelligence (IQ > 85) and performance at average in all standardized tests of school achievement (T 40 in reading, spelling, arithmetic). Table 1 summarizes the five groups descriptive statistics. On average, the CDSS and SLI + CDSS groups performed significantly lower on the mathematics abilities test than did the C, DYS, and SLI + DYS groups. At the same time, the DYS, SLI + DYS, CDSS, and SLI + CDSS groups scored significantly lower on spelling and reading tests than the C group did. Inspection of gender distribution patterns across learning disorder groups showed that more (60%) children with CDSS were female, whereas more children with DYS (60%), SLI + DYS (81%), and SLI + CDSS (61%) were male. Analysis of variance revealed that the five experimental groups did not differ significantly in terms of age, F (4, 107) = 1.17, η 2 =.04, p =.329. The groups differed significantly in terms of intelligence, F (4, 107) = 8.11, η 2 =.23, p =.001. We, therefore, included general intelligence as covariate in all subsequent analyses. All of the children receiving SLE completed additional language measures. For receptive and expressive vocabulary, we carried out the computerized German vocabulary and word finding test for 6- to 10-year-old children (WWT 6 10; Glück, 2007). For grammar, we used the subtests of plural formation

6 Working Memory Functioning in Children With Learning Disorders and SLI 303 Table 1. Means (SDs) for descriptive characteristics of subgroups: sex, age, IQ, DEMAT mathematic T scores, WRT spelling T scores, and SLT word and nonword reading T scores DYS (n = 30) SLI + DYS (n = 16) CDSS (n = 19) SLI + CDSS (n = 18) C (n = 30) Sex (male/female) 18/12 13/3 8/11 11/7 15/15 Age (months) IQ (7.31) (9.65) (6.93) (7.67) (6.41) Mathematic (8.19) (8.60) (5.77) (5.74) (5.51) Spelling (4.83) (3.83) (6.30) (3.62) (6.42) Word reading (7.02) (7.96) (8.32) (8.03) (8.42) Nonword reading (8.06) (10.37) (11.42) (11.34) (7.51) Note. C= normally performing control children matched for chronological age; CDSS = children with combined disorder of scholastic skills; DYS = children with dyslexia; SLI + CDSS = children with specific language impairment and combined disorder of scholastic skills; SLI + DYS = children with specific language impairment and dyslexia. (Plural-Singular bildung) and imitation of grammatical structures (Imitation grammatischer Strukturformen); and for language comprehension, we used the subtest understanding of grammatical structures (Verstehen grammatischer Strukturformen). These measures are all part of the Heidelberger Sprachentwicklungstest (H-S-E-T; Grimm & Schöler, 1991). Table 2 illustrates our findings that both the SLI + DYS and SLI + CDSS groups performed below average on language tasks (exception: receptive vocabulary of the SLI + DYS group). All children in the SLE subgroups met the diagnostic criteria for SLI: (a) IQ 80 and (b) below-average language scores (T <40) for vocabulary, grammar, and language comprehension. Working memory assessment Working memory was assessed by a battery of 16 tasks: 7 phonological tasks (memory spans for digits, one-syllable and threesyllable words, one-syllable and three-syllable nonwords, and images; nonword repetition), 5 visual spatial tasks (memory span for locations, matrix span, corsi-block), and 4 central executive tasks (double span, backward spans for one-syllable words and digits, counting span). A detailed description of all tasks follows below. Table 2. Means (SDs) for language characteristics of SLI subgroups: expressive and receptive vocabulary T scores, imitation of grammatical structures and plural-forming T scores, and language comprehension T scores Vocabulary Grammar Expressive Receptive Imitation Of Grammatical Structures Plural Forming Language Comprehension SLI + DYS (17.27) (19.10) (4.39) (8.22) (6.75) SLI + CDSS (18.52) (10.96) (0.00) (8.36) (4.34) Note. SLI+ CDSS = children with specific language impairment and combined disorder of scholastic skills; SLI + DYS = children with specific language impairment and dyslexia.

7 304 TOPICS IN LANGUAGE DISORDERS/OCTOBER DECEMBER 2013 Phonological loop The digit span task is one of the conventional measures used to assess phonological short-term capacity. A series of one to nine digits was presented acoustically at a rate of one digit per second, starting with two and continuing up to a maximum of eight digits. Participants had to repeat the digits immediately in the presented order. The one-syllable and threesyllable word span tasks and the onesyllable and three-syllable nonword span tasks were presented in the same manner as the digit span measure. In the one-syllable and three-syllable word span tasks, familiar German nouns (e.g., Stern = star, Fisch = fish, Erdbeere = strawberry, Briefkasten = letterbox) were used; the one-syllable and three-syllable nonword span tasks are wordlike nonwords (e.g., fen, sim, bestrugeln, reseubelt). In the images span task, participants were presented a series of pictures of easily recognizable objects (e.g., sun, umbrella, door, car) on a computer screen and were asked to recall them in the order of presentation. This is considered a phonological loop task in which the phonological information is presented visually instead of acoustically because the pictures had to be named internally in order to recall them and report them by name. The German nonword repetition task was developed by Hasselhorn and Körner (1997). Children had to repeat 24 word-like nonwords of 2, 3, or 4 syllables immediately after their presentation. Nonwords of different lengths were presented acoustically in random order. The number of correctly repeated nonwords was taken as the score for this task. This task is not a span task, as there was an immediate repetition after each word. Visual spatial sketchpad In the location span task, children were shown a series of green dots at different locations on a 3 3 matrix and asked to recall these locations in the correct order. Corsiblock tasks were used to assess the dynamic spatial component of visual spatial memory. Nine red blocks were nailed in random positions on a gray board ( cm). The experimenter tapped a sequence of blocks at therateofonepersecond.thechildthen attempted to reproduce the sequence of taps in the correct order. We used two variations of the Corsi-block task: simple sequences involving short distances between blocks without path crossings, and complex sequences involving long distances between blocks with path crossings. A matrix span task was incorporated in the battery as well to measure the static component of the visual spatial sketchpad. This task assesses memory for random visual spatial patterns of increasing complexity. Patterns of white and black boxes in a 4 4 matrix were presented on the computer, beginning with two black boxes and continuing up to a maximum of eight black boxes. Immediately after presentation, children were asked to reproduce the pattern in a blank matrix. Two variations of this task were implemented as well: a simple matrix span with the black boxes arranged in simple patterns and a complex matrix span with the black boxes located at some distance from one another. Central executive Measures of the central executive are those that require remembering and processing at the same time. The same items were used for the backward digit and word span tasks as for the forward spans, the only difference being that participants were required to recall the sequences of items in reverse order. In addition, a double span task was implemented to assess the children s ability to coordinate the functioning of the phonological loop and the visual spatial sketchpad. The same pictures as in the images span task were presented but this time in different locations on a3 3 matrix. Children had to recall the pictures simultaneously by verbally recoding the semantic content (phonological demand) and their location (visual spatial demand) in the order of presentation. Thus, this task is properly viewed as a central executive task

8 Working Memory Functioning in Children With Learning Disorders and SLI 305 because of its coordinative requirements. It is not a dual task because there is only one reaction required: remember the correct pictures in the correct order and location. The complex counting span task, a measure of storage and processing efficiency, was based on a task designed by Case, Kurland, and Goldberg (1982). A series of yellow circles (target items) and squares (distractor items) was presented in a random, computergenerated pattern. Children were instructed to count the number of circles. Subsequently, another map was presented and children again had to count the number of circles. Finally, the experimenter asked the child to recall the number of circles counted on each map. The number of maps presented per sequence was steadily increased up to a maximum of eight. Stop criterion We used the same stop criterion for all span tasks. The length of the sequences presented was increased gradually, beginning with a minimum of two, and increasing to a maximum of eight items. There were four trials at each sequence length. If an error was made, the child was given a second attempt at an item of the same length. If a child succeeded on two successive trials of the same length, the task continued with the next span length. If a child failed on two successive trials of the same length, he or she was not presented with any further sequences of the same length, but with a sequence of one item shorter. The dependent measure for all span tasks was the longest sequence of items repeated in correct order. Children were credited an extra onefourth point (0.25) if they repeated a further sequence of the same length correctly (e.g., a score of 5.25 was awarded if two of four 5-item sequences were recalled correctly, 5.5 if three of four sequences, and 5.75 if all four sequences were recalled correctly). Procedure We administered standardized tests for spelling, reading, arithmetic, intelligence, and working memory individually in two separate sessions with children with SLI and children with learning disabilities. The DEMAT and WRT measures were carried out with control group children in classroom learning groups. All other tests were conducted individually within a period of 3 weeks. Except for the corsi-block task, all working memory tasks were administered by computer. The order of presentation of the working memory tasks was the same for all children (images span, location span, double span, one-syllable word span, three-syllable word span, corsi-block, nonword repetition, backward word span, backward digit span, counting span, digit span, matrix span, one-syllable nonword span, and three-syllable nonword span) and was carried out in one session. RESULTS The first question of our study targeted working memory functioning of children with DYS with and without SLI. To answer this question, we compared children in the DYS, SLI + DYS, and control groups for each working memory subsystem separately. Table 3 presents means and standard deviations for all working memory measures by the three groups. The scores of the seven tasks assessing the phonological loop functioning were entered into a multivariate analysis of variance (MANCOVA). The multivariate main effect proved to be significant, F (14, 136) = 7.53, η 2 =.437, p <.001. The univariate tests also showed significant differences between groups for all phonological tasks (images span, F (2, 73) = 12.51, η 2 =.255, p <.001; digit span, F (2, 73) = 20.26, η 2 =.357, p <.001; one-syllable word span, F (2, 73) = 14.00, η 2 =.277, p <.001; three-syllable word span, F (2, 73) = 12.85, η 2 =.260, p <.001; one-syllable nonword span, F (2, 73)= 21.43, η 2 =.370, p <.001; three-syllable nonword span, F (2, 73) = 12.53, η 2 =.255, p <.001; nonword repetition, F (2, 73) = 82.44, η 2 =.693, p <.001). In the same way, the scores of the five tasks assessing the visual spatial sketchpad were entered into a second MANCOVA. In this case,

9 306 TOPICS IN LANGUAGE DISORDERS/OCTOBER DECEMBER 2013 Table 3. Means (SDs) for working memory measures of subgroups and post hoc tests DYS SLI + DYS C DYS/C Post Hoc Test, p SLI + DYS/C Post Hoc Test, p DYS/SLI + DYS Post Hoc Test, p Phonological loop Images span 4.22 (0.77) 3.41(0.61) 4.60 (0.84).151 < Digit span 4.63 (0.64) 3.88 (0.83) 5.19 (0.61).005 < One-syllable word span 4.28 (0.74) 3.50 (0.60) 4.62 (0.66).149 < Three-syllable word span 3.64 (0.47) 3.35 (0.45) 3.86 (0.43).154 < One-syllable nonword span 3.47 (0.89) 2.92 (0.60) 4.27 (0.50) <.001 < Three-syllable nonword span 1.33 (1.22) 1.06 (1.10) 2.42 (0.74) <.001 < Nonword repetition (3.13) 9.56 (3.86) (1.78) <.001 <.001 <.001 Visual spatial sketchpad Location span 5.27 (1.00) 5.50 (1.31) 4.98 (0.80) Corsi-block simple 5.68 (1.34) 6.08 (1.05) 5.77 (1.36) Corsi-block complex 4.80 (0.85) 5.17 (0.91) 4.98 (1.08) Matrix span simple 6.72 (1.11) 6.61 (1.62) 6.53 (1.29) Matrix span complex 4.45 (1.63) 4.23 (1.97) 4.72 (1.52) Central executive Backward digit span 3.45 (0.66) 3.31 (0.64) 3.90 (0.68) Backward word span 3.58 (0.56) 3.23 (0.54) 3.82 (0.63) Double span 3.78 (0.76) 3.33 (0.55) 4.04 (0.72) Counting span 3.81 (0.89) 3.08 (0.46) 4.45 (0.97).013 < Note. C= normally performing control children matched for chronological age; DYS = children with dyslexia; SLI + DYS = children with specific language impairment and dyslexia.

10 Working Memory Functioning in Children With Learning Disorders and SLI 307 the multivariate group effect was not significant, F (10, 140) < 1, η 2 =.060 (univariate tests: location span, F (2, 73) = 1.56, η 2 =.041; corsi-block simple task, F (2, 73) < 1, η 2 =.014; corsi-block complex, F (2, 73) < 1, η 2 =.022; matrix span simple, F (2, 73) < 1, η 2 =.004; matrix span complex, F (2, 73) < 1, η 2 =.013). Third, the scores of the four tasks assessing the central executive were entered into a MANCOVA: here, the multivariate group effect, F (8, 142) = 3.69, η 2 =.172, p =.001, proved to be significant. Univariate tests showed significant differences between groups on all central executive memory tasks (digit backward span, F (2, 73) = 5.37, η 2 =.128, p =.007; word backward span, F (2, 73) = 5.24, η 2 =.126, p =.007; double span, F (2, 73) = 5.38, η 2 =.128, p =.007; counting span, F (2, 73) = 13.71, η 2 =.273, p <.001). Post hoc tests (Tukey, Table 3) for further analysis of group differences revealed that the DYS and control groups differed in phonological loop and central executive functioning for most tasks (forward and backward digit span, one- and three-syllable nonword span, nonword repetition, counting span). The SLI + DYS group exhibited deficits in all phonological and central executive tasks compared with group C. Here, we presume a broad deficit concerning all tasks. These deficits became even more evident in tasks assessing phonological loop and in aspects of central executive compared with children with isolated DYS (images span, digit span, one- and three-syllable word span, one-syllable nonword span, nonword repetition, counting span). Just as we expected, no differences appeared between the groups on tasks assessing the visual spatial sketchpad. In a second step, we compared working memory performance of children who met criteria for learning disorder in reading, writing, and arithmetic only (CDSS) with those who had an additional diagnosis of SLI (SLI + CDSS) with controls (C). Table 4 presents mean scores on all working memory tasks by subgroup. The scores of the tasks assessing the phonological loop were entered into a MANCOVA. The multivariate main effect proved to be significant, F (14, 116) = 11.84, η 2 =.588, p <.001. The univariate tests also showed significant differences between groups for all phonological tasks (images span, F (2, 63) = 20.08, η 2 =.389, p <.001; digit span, F (2, 63) = 41.85, η 2 =.571, p <.001; one-syllable word span, F (2, 63) = 30.69, η 2 =.493, p <.001; three-syllable word span, F (2, 63) = 28.26, η 2 =.473, p <.001; one-syllable nonword span, F (2, 63) = 26.63, η 2 =.458, p <.001; three-syllable nonword span, F (2, 63) = 27.70, η 2 =.468, p <.001; nonword repetition, F (2, 63) = 90.73, η 2 =.472, p <.001). Second, the scores of the five tasks assessing the visual spatial sketchpad were entered into a second MANCOVA: the multivariate group effect, F (10, 122) = 2.65, η 2 =.179, p =.006, and all univariate tests (location span, F (2, 64) = 3.06, η 2 =.087, p =.047; corsi-block simple task, F (2, 64) = 3.27, η 2 =.093, p =.045; corsi-block complex, F (2, 64) = 7.93, η 2 =.199, p =.001; matrix span simple, F (2, 64) = 6.52, η 2 =.169, p =.003; matrix span complex, F (2, 64) = 6.71, η 2 =.137, p =.002) proved to be significant. In the same way, the scores of the four tasks assessing the central executive were entered into a MANCOVA. Here, the multivariate group effect proved to be significant, F (8, 124) = 6.10, η 2 =.282, p <.001. Univariate tests showed significant differences between groups on all central executive memory tasks (digit backward span, F (2, 64) = 8.48, η 2 =.209, p =.001; word backward span, F (2, 64) = 14.13, η 2 =.306, p <.001; double span, F (2, 64) = 13.90, η 2 =.303, p <.001; counting span, F (2, 64) = 28.94, η 2 =.475, p <.001). Post hoc tests (Tukey), illustrated in Table 4, demonstrate that both clinical groups (CDSS and SLI + CDSS) displayed phonological working memory deficits compared with controls (all phonological tasks). Deficits were more pronounced for children with

11 308 TOPICS IN LANGUAGE DISORDERS/OCTOBER DECEMBER 2013 Table 4. Means (SDs) for working memory measures of subgroups and post hoc tests CDSS SLI + CDSS C CDSS/C Post Hoc Test p SLI + CDSS/C Post Hoc Test, p SLI + CDSS/CDSS Post Hoc Test, p Phonological loop Images span 3.68 (0.56) 3.34 (0.54) 4.60 (0.84) <.001 < Digit span 4.21 (0.50) 3.65 (0.60) 5.19 (0.61) <.001 < One-syllable word span 3.43 (0.60) 3.22 (0.44) 4.62 (0.66) <.001 < Three-syllable word span 3.24 (0.47) 2.92 (0.38) 3.86 (0.43) <.001 < One-syllable nonword span 3.21 (0.98) 2.88 (0.55) 4.27 (0.50) <.001 < Three-syllable nonword span 1.22 (0.83) 0.36 (0.83) 2.42 (0.74) <.001 < Nonword repetition (4.57) 7.35 (3.93) (1.78).018 <.001 <.001 Visual spatial sketchpad Location span 4.36 (0.78) 4.90 (1.18) 4.98 (0.80) Corsi-block simple 4.95 (1.13) 5.81 (1.01) 5.77 (1.36) Corsi-block complex 3.80 (1.23) 4.97 (0.39) 4.98 (1.08) Matrix span simple 5.26 (1.16) 6.08 (1.04) 6.53 (1.29) Matrix span complex 3.22 (1.03) 4.01 (1.73) 4.77 (1.52) Central executive Backward digit span 3.26 (0.47) 3.07 (1.01) 3.90 (0.68) Backward word span 3.20 (0.32) 3.10 (0.47) 3.82 (0.63) <.001 < Double span 3.34 (0.55) 3.14 (0.54) 4.04 (0.72).001 < Counting span 3.22 (0.73) 2.82 (0.34) 4.45 (0.97) <.001 < Note. C= normally performing control children matched for chronological age; CDSS = children with combined disorder of scholastic skills; SLI + CDSS = children with specific language impairment and combined disorder of scholastic skills.

12 Working Memory Functioning in Children With Learning Disorders and SLI 309 SLI + CDSS in comparison with children with CDSS only (digit span, one-syllable word span, three-syllable nonword span, nonword repetition). In contrast, only children with CDSS (without SLI) showed deficits associated with visual spatial sketchpad compared with controls (all visual spatial tasks), whereas children with SLI + CDSS did not. With regard to central executive functioning, both disability groups differed from the control group but not from each other (CDSS and SLI + CDSS: deficits in all central executive tasks). DISCUSSION Researchers currently regard deficits in working memory functioning as one major characteristic for language impairment and learning disorders (Archibald & Gathercole 2006a, 2006b; Schuchardt et al., 2008). Our study investigated the question of whether children with learning disorders and language impairment present with the same working memory deficits. Comparing working memory profiles of children with learning disorders (DYS or CDSS) only with profiles for children with additional language impairment (SLI) was intended to help us to discover whether patterns of working memory deficits are disorder-specific. In summary, our results suggested that learning disorders (in reading, spelling, and calculating) and learning disorders combined with SLI share some deficits in underlying working memory and are also associated with distinct patterns of working memory difficulties. Deficits with regard to the phonological loop and central executive were found for learning disorders both with and without SLI; however, the phonological impairment was more severe and broader in children who met criteria for SLI. In fact, all clinical groups displayed significant deficits in tasks involving the phonological loop. Children with combined language and learning impairment (SLI + DYS and SLI + CDSS) performed even worse, however, on the majority of phonological tasks than children with isolated DYS or CDSS. Incidentally, we found that the threesyllable nonword span did not differentiate the groups because of significant floor effects. On the contrary, we detected the highest difference in performance on nonword repetition tasks for measuring the phonological store. The finding that children with additional known SLI scored even lower on phonological loop tasks than children with DYS and CDSS who had not been referred for SLE is partly in line with results of other studies (Archibald & Gathercole, 2006c; Archibald & Gathercole, 2007; Baird et al., 2011; de Bree et al., 2010). Nonword repetition is viewed as a rather pure indicator for the phonological store, because the task does not imply retrieval from long-term memory. Thus, children with the additional diagnosis of SLI seem to be more likely to exhibit a particularly pronounced storage impairment. Extending these findings, Hasselhorn and Werner (2000) conducted a study in which they varied acoustic presentation as well as syllable length in nonwords. They highlighted half of the words with white noise to lead to acoustic distortion. In their extended model of the phonological loop, Hasselhorn, Grube and Mähler (2000) regarded the acoustic distortion effect as a marker for quality of the phonological store. Children with SLI and language-matched controls performed significantly worse with increasing syllable length on acoustically distorted tasks. The performance gap between the groups was reduced in a condition in which children had to repeat distorted three- or four-syllable nonwords. Hasselhorn and Werner (2000) concluded that children with SLI are disturbed less by white noise (with increasing syllable length) than language-matched controls, because children with SLI benefit less from accurate acoustic presentation. The authors concluded that working memory impairment in children with SLI, therefore, is due to reduced processing quality in the phonological store, especially when the soundscapes exceed a certain number of information units.

13 310 TOPICS IN LANGUAGE DISORDERS/OCTOBER DECEMBER 2013 In addition to the phonological working memory deficits, all four clinical groups displayed deficits in central executive functioning. Therefore, deficits in central executive functioning appear to be characteristic for children with DYS and CDSS (Schuchardt et al., 2008) as well as for children with SLI (Archibald & Gathercole, 2006b; Marton & Schwartz, 2003; Montgomery & Evans, 2009). Nevertheless, it should be considered that most of the central executive tasks used also involve the participation of the phonological loop to some extent because phonological information has to be processed. Therefore, we cannot rule out the possibility that the phonological deficit is the predominant impairment in children with learning disorders with or without additional SLI. When we look at the visual spatial sketchpad, we find different patterns of results. In line with earlier studies, we could observe that children with CDSS exhibit deficits in this domain (Maehler & Schuchardt, 2009; Schuchardt et al., 2008). Interestingly, we could not provide evidence for disadvantages in visual-spatial working memory for the children with CDSS + SLI (see Nithart et al., 2009). As only children with combined learning disorder (CDSS) showed deficits in the visual spatial working memory, it may be that visual spatial malfunctions influence arithmetic problems of these children. In contrast, we assume that children with additional language problems (CDSS + SLI) could exhibit arithmetic problems because of language problems, as their visual spatial working memory turned out to be unimpaired. Findings of Donlan et al. (2007) and Fazio (1999) point to the same line of argument. Thus, we would expect mathematical problems in children with SLI especially on tasks that severely depend on language comprehension but not on tasks that can be solved by intact visual spatial perception and memory. In summary, we would conclude that analyzing working memory functioning in-depth could help us to differentiate between various disorders according to underlying cognitive deficits. Certainly, the assessed patterns of deficits in different clinical groups do not allow for distinct diagnoses of specific disorders. Furthermore, other disorders besides the ones included in this study are associated with working memory problems. But at least we could become more precise in recommending intervention measures that rely on different strengths and difficulties of the children. According to the results of this study, phonological and central executive problems must be expected in children with learning disorders with or without SLI. Therefore, teaching should take these deficits into account and try to reduce the task demands with regard to the amount of information to be processed or integrated. And children with SLI should be supported to profit from their apparently intact visual spatial memory, for example, by providing training on relevant memory strategies or visual supports to language intervention activities. Future research is needed to evaluate working memory training programs in order to explore the possibility to overcome working memory deficits. REFERENCES Archibald, L. M., & Gathercole, S. E. (2006a). Visuospatial immediate memory in language impairment. Journal of Speech, Language, and Hearing Research, 49, Archibald, L. M., & Gathercole, S. E. (2006b). Shortterm and working memory in specific language impairment. International Journal of Language & Communication Disorders, 41, Archibald, L. M., & Gathercole, S. E. (2006c). Nonword repetition in specific language impairment. Psychonomic Bulletin & Review, 14, Archibald, L. M., & Gathercole, S. E. (2007). Nonword repetition in specific language impairment: More than a phonological short-term memory deficit. Psychonomic Bulletin & Review, 14, Baddeley, A. D. (1986). Working memory. Oxford: University Press.

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