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Page 1: Learning About Learning Disabilities || Learning Disabilities and Memory

27Learning about Learning Disabilities© 2012 Elsevier Inc.

All rights reserved.2012

Learning Disabilities and MemoryH. Lee Swanson, and Danielle StomelGraduate School of Education, Educational Psychology/Special Education, University of California, CA 92521, USA

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Chapter Contents

Introduction 27A Historical Perspective 28Understanding Memory Differences for Students with LD 31

Parallels to Normal Memory Development 32Mapping Memory Components that Might Be Deficient for Students with LD 33

Everyday Memory 43Memory Intervention 44

Memory Strategies Serve Different Purposes 45Good Memory Strategies for NLD Students are not Necessarily Good Strategies

for Students with LD and Vice Versa 45Effective Memory Strategies do not Necessarily Eliminate Processing Differences 46The Strategies Taught are not Necessarily the Ones Used 46Memory Strategies in Relation to a Student’s Knowledge Base and Capacity 47Comparable Memory Strategy May not Eliminate Performance Differences 47Memory Strategies Taught do not Necessarily become Transformed into Expert

Strategies 48Strategy Instruction Must Operate on the Law of Parsimony 48Training WM Directly 49

Summary and Conclusions 51References 52

CHAPTER

INTRODUCTION

Memory is the ability to encode, process, and retrieve information that one has been exposed to. As a skill, it is inseparable from intellectual function-ing and learning. Individuals deficient in memory skills, such as children and adults with learning disabilities (LD), would be expected to have difficulty on a number of academic and cognitive tasks. Although memory is linked to performance in several academic (e.g., reading) and cognitive areas (e.g., problem solving), it is a critical area of focus in the field of LD for three rea-sons. First, it reflects applied cognition; that is, memory functioning reflects

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all aspects of learning. Second, several studies suggest that the memory skills used by students with LD do not appear to exhaust, or even to tap, their ability, and therefore we need to discover instructional procedures that capi-talize on their potential. Finally, several intervention programs that attempt to enhance the overall cognition of children and adults with LD rely on principles derived from memory research. This chapter characterizes and selectively reviews past and current research on memory skills, describes the components of processing that influence memory performance, and dis-cusses the implications of memory research for the instruction of children and adults with LD. A more comprehensive, historical review and analy-sis of contemporary memory research on LD is reported elsewhere (e.g., Swanson, 2011; Swanson, Cooney, & McNamara, 2004).

A HISTORICAL PERSPECTIVE

The earliest link between LD and memory was established in the litera-ture on reading disabilities in the works of Kussmaul. In 1877, Kussmaul called attention to a disorder he labeled “word blindness”, which was characterized as an inability to read, although vision, intellect, and speech were normal. Following Kussmaul’s contribution, several cases of read-ing difficulties acquired by adults due to cerebral lesions, mostly involving the angular gyri of the left hemisphere, were reported (see Hinshelwood, 1917, for a review). In one important case study published by Morgan (1896), a 14-year-old boy of normal intelligence had difficulty recall-ing letters of the alphabet. He also had difficulty recalling written words, which seemed to convey “no impression to this mind”. Interestingly, the child appeared to have good memory for oral information. This case study was important because word blindness did not appear to occur as a result of a cerebral lesion. After Morgan’s description of this condition, desig-nated as a specific reading disability, research on memory was expanded to include children of normal intelligence who exhibited difficulties in read-ing. Hinshelwood’s (1917) classic monograph presents a number of case studies describing reading disabilities in children of normal intelligence with memory problems. On the basis of these observations, Hinshelwood inferred that reading problems of these children were related to a “patho-logical condition of the visual memory center” (p. 21).

At the same time Hinshelwood’s monograph appeared, a little known text by Bronner (1917) reviewed case studies linking memory difficulties to children of normal intelligence. For example, consider Case 21:

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A majority of case studies reviewed in Bronner’s text suggested that immediate (short-term) memory of children with reading disabilities was deficient and that remote (long-term) memory was intact. Bronner also noted that little about memory and its application to complex learning activities was known. For example, the author stated:

Very many practically important laws of memory have not yet been determined; those most firmly established concern themselves mainly with nonsense or other type of material quite unlike the activities of everyday life. In a common sense way we are aware that both immediate and remote memory are essential, that we need to remember what we see and hear … that to remember an idea is probably more useful in general, than to have a good memory for rote material, but a defect for the latter may be of great significance in some kinds of school work.

(Bronner, 1917, p. 110)

Researchers from the 1920s to the 1950s generally viewed reading dif-ficulties as being associated with structural damage to portions of the brain that support visual memory (e.g., see Geschwind, 1962, for a review; also see Monroe, 1932). A contrasting position was provided by Orton (1925, 1937), who suggested that reading disorders were reflective of a neurologi-cal maturational lag resulting from a delayed lateral cerebral dominance for language. Orton described the phenomenon of a selective loss or dimin-ished capacity to remember words as strephosymbolia (twisted symbols). Orton (1937) noted that:

Although these children show many more errors of a wide variety of kinds it is clear that their difficulty is not in hearing and not in speech mechanism … but in recalling words previously heard again or used in speech, and that one of the outstanding obstacles to such recall is remembering (emphasis added) all of the sounds in their proper order.

(Orton, 1937, p. 147)

Henry J., 16 years old, was seen after he had been in court on several occa-sions. The mental examination showed that the boy was quite intelligent and in general capable, but had a very specialized defect. The striking feature of all the test work with this boy was the finding that he was far below his age in the matter of rote memory. When a series of numerals was presented to him auditorially, he could remember no more than four. His memory span for numerals presented visually was not much better … he succeeded here with five. Memory span for syllables was likewise poor … On the other hand when ideas were to be recalled, that is, where memory dealt with logical material, the results were good. (Bronner, 1917, p. 120)

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In cases of visual memory, Orton stated that such children with read-ing disabilities have major difficulties in “recalling the printed word in terms of its spatial sequence of proper order in space” (p. 148). Thus, for Orton, reading disabled children’s memory difficulties were seen as reflect-ing spatial sequences in visual memory or temporal sequences in auditory memory. Although the conceptual foundation of much of Orton’s research was challenged in the 1970s (see Vellutino, 1979, for a review), much of the clinical evidence for linking LD and memory processes was established from the earlier clinical studies of Morgan, Hinshelwood, and Orton.

It was not until the late 1960s and early 1970s that experimental (non-clinical) studies appeared comparing children with LD and nondisabled (NLD) children’s performance on memory tasks. The majority of these studies focused on modality-specific memory processes (i.e., auditory vs. visual memory) and cross-modality (e.g., visual recognition of auditori-ally presented information) instructional conditions. For example, Senf and Feshbach (1970) found differences between good and poor readers’ memory on cross-modality presentation conditions. That is, students were compared on their recall of digits presented auditorially, visually, and audio-visually and retrieval responses were verbal or written. The sample with LD exhibited poor recall of stimuli organized into audiovisual pairs, which was attributed to problems of cross-modality matching. Older, normal achiev-ing children recalled the digits in audiovisual pairs more accurately than their younger counterparts, whereas older children with LD recalled no bet-ter than younger children with LD. The sample with LD also exhibited a higher prevalence of visual memory errors. The implication of this research was that some prerequisite skills of pairing visual and auditory stimuli had not developed in the children with LD, and the possession of these skills was essential for reading. In contrast to this study, Denckla and Rudel (1974) found that poor recall of children with LD was not related to visual encod-ing errors, but rather to temporal sequencing. Their results suggested that children who had difficulties in temporal sequencing would have difficulty recalling information from spatial tasks or tasks that required matching of serial and spatial stimuli (as in the study of Senf & Feshbach, 1970). To sum-marize, studies in the late 1960s and early 1970s, although contradictory, did establish that children with LD experienced memory difficulties on labo-ratory tasks that required the sequencing of information presented visually and auditorially. Differences in results were most likely due to variations in how the ability groups were defined and selected.

We now turn to a discussion of the conceptualizations related to mem-ory problems of children and adults with LD from the mid 1970s to the

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mid 1980s. During this time period, memory performance of children and adults with LD was strongly influenced by the hypothesis that variations in memory performance are partly rooted in children’s acquisition of mne-monic strategies. Strategies are deliberate, consciously applied procedures that aid in the storage and subsequent retrieval of information. Studies dur-ing this time period focused on memory activities such as clustering, elabo-ration, and rehearsal. The emphasis in these studies was on teaching children with LD under various conditions or with different types of memory strate-gies how to remember presented material (e.g., see Scruggs & Mastroperi, 2000, for a review). In general, earlier studies showed that children with LD could be taught through direct instructions (e.g., Gelzheiser, 1984), mod-eling (e.g., Dawson, Hallahan, Reaves, & Ball, 1980), and reinforcement (e.g., Bauer & Peller-Porth, 1990) to use some simple strategies that they do not produce spontaneously (e.g., Dallego & Moely, 1980). Further, the strategy hypothesis was generalized into other areas beside memory, such as reading comprehension (e.g., Wong & Jones, 1982), writing (e.g., Graham & Harris, 2003), mathematics (e.g., Montague, 1992), and problem solving (e.g., Borkowski, Estrada, Milstead, & Hale, 1989).

Since the 1990s, the majority of memory research has moved in a different direction, towards an analysis of nonstrategic processes that are not necessarily consciously applied. Many of these studies are framed within Baddeley’s (Baddeley, 1986, 2000, 2007; Baddeley & Logie, 1999) multiple component model (to be discussed; see Alloway, 2007; Alloway & Passolunghi, 2009; Berg, 2008; Gathercole, Alloway, Willis, & Adams, 2006; Swanson, Howard, & Sáez, 2006). The major motivation behind this movement has been that important aspects of memory performance are often disassociated with changes in mnemonic strategies, and that signifi-cant differences remain in performance between children with and with-out LD after using optimal strategies (a strategy shown advantageous in the majority of studies). Prior to reviewing this current focus of mem-ory research, however, an understanding of the research conducted on the development of memory in children with LD during the late 1970s to the early 1990s is necessary.

UNDERSTANDING MEMORY DIFFERENCES FOR STUDENTS WITH LD

When accounting for where, how and why students with LD’s memory is deficient in comparison to peers, two broad perspectives have been adopted, reflected in: (a) studies that parallel normal child development

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in memory and (b) studies that identify memory components in which children or adults with LD are deficient.

Parallels to Normal Memory DevelopmentThere is some agreement among researchers that what we know about the memory of children with LD is somewhat paralleled by what we know about the differences between older and younger children’s memory (e.g., Jarrold & Bayless, 2007; Swanson, 1999a, 2003; Swanson, Jerman, & Zheng, 2008). Such parallels in performance do not mean that children with LD experience a lag in all memory processes or that faulty mem-ory performance is primarily related to immature development. Rather, faulty memory performance reflects overt performance in some memory areas that is comparable to young children. The research on chronologi-cally age matched children with and without LD parallels the research on younger versus younger NLD children and shows that performance differ-ences (a) emerge on tasks that require the use of cognitive strategies (e.g., rehearsal and organization); (b) emerge on effortful memory tasks, but not for tasks requiring automatic processing; (c) are influenced by the individ-ual’s knowledge base; and (d) are influenced by the individuals’ awareness of their own memory processes (metacognition).

Perhaps one of the most significant studies in terms of bringing research in memory on students with LD into a developmental perspec-tive was conducted by Tarver, Hallahan, Kauffman, and Ball (1976). In a first study, they compared children with LD of approximately 8 years of age to normally-achieving boys of the same age on a serial recall task of pictures that included central and incidental information. They found that the serial position curve of NLD children revealed the common primacy-recency effect (remembering the first and last presented items better than the middle items), whereas the performance of children with LD revealed a recency effect only. In a second study, they compared boys with LD who were 10 and 13 years of age on the same tasks. They found that the 10 and 13-year-old children with LD exhibited both a primacy and recency effect for nonrehearsal and rehearsal conditions. For both studies, an analysis of central recall (children attend to specific items based on experimenter instructions) in the three age groups revealed a con-stant age related increase in overall recall and in primacy (recalling the first few items presented) performance. The normal achievers recalled more information that was central to the task when compared to children with LD, whereas children with LD recalled more incidental information

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than normal achievers. Thus, although children with LD were deficient in selective attention, their selective attention improved with age. These results were interpreted as reflecting a developmental lag, in that students with LD were viewed as delayed in their utilization of the strategies for serial recall (verbal rehearsal) and selective attention. Earlier studies that covered some of the same developmental themes as the Tarver et al. (1976) study were Torgesen and Goldman (1977) in which they investigated the role of rehearsal on serial and free recall performance, Swanson (1977) in which he investigated the role of primacy performance on the non-verbal serial recall of visual information, Bauer (1977) in which he investigated the role of rehearsal and serial recall, and Wong (1978), in which she inves-tigated the effect of cued recall and organization on children with LD.

Mapping Memory Components that Might Be Deficient for Students with LDThus, earlier research established some parallels between the performance of younger children and those of older children with LD. Emerging research also showed that performance of children with LD may reflect deficits and not necessarily immature development. One popular means of explaining the cognitive performance of students with LD was by drawing upon fundamental constructs that are inherent in most models of infor-mation processing. Three constructs are fundamental: (1) a constraint or structural component, akin to the hardware of a computer, which defines the parameters within which information can be processed at a particu-lar stage (e.g., sensory storage, STM, working memory, long-term mem-ory); (2) a strategy component, akin to the software of a computer system, which describes the operations of the various stages; and (3) an executive component, by which learners’ activities (e.g., strategies) are overseen and monitored, particularly in association with WM.

Briefly, the structural components are sensory, short-term, working, and long-term memory. Sensory memory refers to the initial represen-tation of information that is available for processing for a maximum of 3–5 seconds; STM processes information between 3 and 7 seconds and is primarily concerned with storage, via rehearsal processes. Working memory also focuses on the storage of information as well as the active interpretation of newly presented information plus information from long-term memory, whereas long-term memory is a permanent storage with unlimited capacity. The executive component monitors and coordi-nates the functioning of the entire system. Some of this monitoring may

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be automatic, with little awareness on the individual’s part, whereas other types of monitoring require effortful and conscious processing.

Earlier research relied on a multistore model of memory that viewed information as flowing through these component stores in a well-regulated fashion, progressing from the sensory register, to STM, and finally to long-term memory. These stores can be differentiated in children’s func-tioning by realizing that (a) STM has a limited capacity, and thus makes use of rehearsal and organizing mechanisms; (b) storage in long-term memory is mostly semantic; and (c) two critical determinants of forgetting in long-term memory are item displacement and interference, possibly as a result of a lack of retrieval strategy.

In general, research on the sensory register for children with LD suggests it is somewhat intact (see Eden, Stein, Wood, & Wood, 1995; Santiago & Matos, 1994 for review). Some earlier reviews (e.g., see Worden, 1986) have also suggested that the long-term memory of children with LD is intact, but the strategies necessary to gain access to this information are impaired. However, a good deal of research has focused on ways in which STM, as well as WM and associated processes, might be problematic. Thus, attention in the remainder of this section focuses primarily in these two areas.

Short-Term Memory (STM)One area that has received some consensus is that STM for verbal infor-mation is deficient in children and adults with LD (Swanson & Hsieh, 2009; Swanson & Jerman, 2006; Swanson, Zheng, & Jerman, 2009). The majority of this research has suggested that, for children with LD, the lack or inefficient use of a phonological code (sound representation within the child’s mind) impairs reading development (e.g., Siegel, 1993a,b). Several researchers have found that good and poor readers differ in the way they access phonological information in memory (see Siegel, 2003, for a review).

An earlier seminal study by Shankweiler, Liberman, Mark, Fowler, and Fischer (1979) compared the ability of superior, marginal, and poor sec-ond grade readers to recall rhyming and nonrhyming letter strings. The superior readers were found to have more difficulty recalling the rhyming letter strings than the nonrhyming strings. Poor readers, however, appeared to perform comparably on rhyming and nonrhyming tasks. The authors suggested that the phonological confuseability created by the rhyming let-ters interfered with good readers’ recall because these readers relied on phonological information to a greater degree than poor readers.

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Thus, an interaction is usually found, in which poor readers perform better on “rhyming-word and similar letter-sounding tasks” because they have poor access to a phonological code (e.g., Shankweiler et al., 1979). That is, good readers recall more information for words or letters that have distinct sounds (e.g., mat vs. book, A vs. F) than words or letters that sound alike (mat vs. cat, b vs. d). In contrast, poor readers are more com-parable in their recall of similar and dissimilar words or sounds than skilled readers. This finding suggests that good readers are disrupted when words or sounds are alike because they process information in terms of sound (phonological) units. In contrast, poor readers are not efficient in process-ing information into sound units (phonological codes) and, therefore, are not disrupted in performance if words or letters sound alike.

Because STM is clearly the most widely researched area related to the cognitive processing problems of students with LD, a comprehensive meta-analysis (quantitative synthesis) was conducted comparing the per-formance of students with and without LD on STM tasks (O’Shaughnessy & Swanson, 1998). The analysis covered articles published in a 20-year period. To be included in the analysis, each study must have: (a) directly compared readers with LD to average readers, as identified on a standard-ized reading measure, on at least one short-term measure; (b) reported standardized reading scores which indicated that students with LD were at least 1 year below grade level; and (c) reported intelligence scores for stu-dents with LD which were in the average range (85 to 115). Although the search resulted in approximately 155 articles on memory and LD, only 38 studies met the criteria for inclusion (24.5%). Effect sizes (ESs) were com-puted for each experiment to reflect the relationship between the mean memory score of the learning disabled group as compared to the mean memory score of the NLD group. Negative values for ES represented poorer immediate memory performance in the learning disabled group (e.g., an ES of −0.50 suggested that the mean score of students with LD was ½ standard deviation below the mean score for normally-achieving students). For comparisons, an ES magnitude of 0.20, in absolute value, is considered small, 0.50 is moderate, and 0.80 is considered large (Cohen, 1988).

Based on a review of the studies included in this analysis, two broad categories were developed to organize the results: studies that used: (1) verbal stimuli and/or (2) nonverbal stimuli. In addition, the following sub-categories were developed to organize each of the broad categories: (a) free recall and serial recall memory tasks; (b) with and without instruction

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in mnemonic strategies; (c) auditory and visual presentation; and (d) age (7–8 years, 9–11 years, 12–13 years, 14–17 years, and 18 years and older). The majority of studies involved 4th, 5th, and 6th grade students. The important findings of the synthesis were as follows:1. The learning disabled group performed more poorly on tasks requir-

ing memorization of verbal information in comparison to the NLD group (an overall mean ES of −0.68).

2. Memory tasks that employed stimuli that could not easily be named, such as abstract shapes, did not produce large differences between good and poor readers (ES = −0.15).

3. Memory tasks that required readers with LD to recall exact sequences of verbal stimuli, such as words or digits, immediately after a series was presented yielded a much greater overall mean ES (ES = −0.80) than nonverbal serial recall tasks (ES = −0.17). Thus, compared to average readers, the relative serial recall performance of students with read-ing disabilities was much poorer with verbal material than it was with nonverbal stimuli.

4. The overall mean ES for studies which provided instructions in mne-monic strategies for verbal stimuli (e.g., rehearsal and sorting items into groups) was −0.54; which was lower, but not much, when compared to studies that did not provide instructions (ES = −0.71). This indicates that although the memory performance of students who are reading disabled improved with training in mnemonic strategies, their perfor-mance was still well below that of average readers.

5. Memory tasks that involved the auditory presentation of verbal stimuli resulted in an overall mean ES of −0.70, while those that involved a visual presentation of verbal stimuli resulted in an overall mean ES of −0.66. Thus, the inferior verbal memory performance of reading dis-abled students appears unrelated to the modality in which a stimulus is received.

6. Memory tasks that involved the visual presentation of nonverbal stim-uli, such as abstract shapes, resulted in an overall mean ES of −0.15. This can be interpreted as a small difference between the average and learning disabled reading groups.

In summary, this quantitative analysis of the literature indicates that chil-dren and adults with LD are inferior to their counterparts on measures of STM. Most critically, students with LD are at a distinct disadvantage com-pared to their normal achieving peers when they are required to mem-orize verbal information. Students with LD have difficulty remembering

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familiar items such as letters, words, and numbers, and unfamiliar items such as abstract shapes that can be named and stored phonetically in mem-ory. Moreover, when a task demands that verbal information be recalled in sequential order, the memory performance of students with LD declines even farther. Because skillful reading involves processing ordered informa-tion (i.e., words are written from left to right and comprised of specific sequences of letters) it seems likely that memory deficits could play a role in reading disabilities. For example, beginning readers must obtain the sounds of words from their written representations. These print-to-sound codes must be stored in memory in order and then blended together, while simultaneously searching LTM for a word that matches the string of sounds. Because low verbal materials (e.g., Geometric Shapes) produce small differences between skilled and learning disabled readers in recall, the memory deficits of readers with LD do not appear to involve general memory ability.

Working MemoryCurrent perspectives on the study of memory in learning disabled sam-ples focus on working memory. Working memory has been applied to poor performance in such academic areas as reading comprehen-sion (e.g., Carretti, Borella, Cornoldi, & De Beni, 2009; De Jong, 1998; Savage, Lavers & Pilly, 2007; Swanson, 1999b), math (Berg, 2008; Geary, Hoard, Bryd-Craven, Nugent, & Numtee, 2007; Swanson & Beebe-Frankenberger, 2004), and writing (Richards et al., 2009; Swanson & Berninger, 1996), as well as general educational attainment (Gathercole, Durling, Evans, Jeffcock, & Stone, 2008; Gathercole, Pickering, Knight, & Stegman, 2004). More recent work has focused on the relationship between working memory and reading disabilities in English language learners (e.g., Swanson, Orosco, Lussier, Gerber, & Guzman-Orth, 2011; Swanson, Sáez, & Gerber, 2006).

The most popular framework used to describe working memory is Baddeley’s multi-component model (1986, 1996, 2000, 2007). Baddeley (1986; Baddeley & Logie, 1999) describes WM as a limited central-executive system that interacts with a set of two passive storage systems used for temporary storage of different classes of information: the speech-based phonological loop and the visual sketchpad. The phonological loop is responsible for the temporary storage of verbal information; items are held within a phonological store of limited duration, and the items are maintained within the store via the process of articulation. The visual

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sketchpad is responsible for the storage of visual-spatial information over brief periods and plays a key role in the generation and manipulation of mental images. Both storage systems are in direct contact with the central executive system. The central executive system is considered to be primar-ily responsible for coordinating activity within the cognitive system, but also devotes some of its resources to increasing the amount of information that can be held in the two subsystems (Baddeley & Logie, 1999). A recent formulation of the model (Baddeley, 2000) also includes a temporary mul-timodal storage component called the episodic buffer. However, the three factor structure has an excellent fit to the WM performance of children (Alloway et al., 2004; Gathercole, Pickering, Ambridge, & Wearing, 2004; Swanson, 2008).

There are correlates in the neuropsychological literature that comple-ment the tripartite structure, suggesting that some functional indepen-dence exists among the systems (e.g., Jonides, 2000; Ruchkin, Berndt, Johnson, Grafman, Rotter, & Canoune, 1999). Functional magnetic res-onance imaging (fMRI) studies suggest separate neural circuitry for the storage and rehearsal components of both the phonological and the visual-spatial system, with phonological system activity mainly located in the left hemisphere and visual-spatial system activity located primar-ily in the right hemisphere (Smith & Jonides, 1997). Executive control processes, on the other hand, are associated primarily with the prefron-tal cortex (e.g., Reichle, Carpenter, & Just, 2000; Smith & Jonides, 1999). Neuropsychological evidence also suggests that children with LD in the areas of reading (RD) and/or math (MD) experience difficulties related to these structures. Based on the type of task, of course, studies suggest that children with RD have processing difficulties related to regions of the frontal lobe (e.g., Lazar & Frank, 1998), left parietal lobe (e.g., Pugh et al., 2000; Shaywitz et al., 1998), as well as problems related to the interhemi-spheric transfer and coordination of information across the corpus callo-sum (e.g., Swanson & Mullen, 1983; Swanson & Obrzut, 1985). Likewise, a casual review of the literature shows that MD has been associated with the left basal ganglia, thalamus, and the left parieto-occipito-temporal areas (e.g., Dehaene & Cohen, 1995, 1997). Damage to these regions may be associated with difficulties in accessing number facts. Clearly, the biologi-cal correlates of the various subcomponents in WM in RD and/or MD samples are just beginning to be identified with advances in technology.

How does this WM formulation help us understand LD better than the concept of STM? First, it suggests that strategies play a smaller role

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in learning and memory than previously thought. This is an important point because some studies do show that performance deficits of chil-dren with LD are not related to rehearsal, per se (e.g., Swanson, 1983a,b). Second, the idea of a WM system is useful because it is viewed as an active memory system directed by a central executive. This is important because the central executive can become a focus of instruction and influence on academic performance. Finally, and most importantly, WM processes are highly related to achievement (e.g., Daneman & Merikle, 1996), whereas with STM less so (Daneman & Carpenter, 1980).

We will briefly review the psychological evidence on those com-ponents of WM that underlie LD (however also see Swanson & Siegel, 2001a,b, for an earlier review).

Executive SystemThe central executive monitors the control processes in WM. There have been a number of cognitive activities assigned to the central executive, including coordination of subsidiary memory systems, control of encoding and retrieval strategies, switching of attention in manipulation of material held related to the verbal and visual spatial systems, and the retrieval of information from LTM (e.g., Baddeley, 1996; Miyake, Friedman, Emerson, Witzki, & Howerter, 2000). Although the executive function has separable operations (e.g., inhibition, updating), these operations share some under-lying commonality (e.g., see Miyake et al., 2000, for a review). Several of these activities have been reduced to three functions: (a) inhibition of irrelevant responses; (b) updating and monitoring of working memory representations; and (c) shifting between mental sets (Miyake et al., 2000). The research appears to support the notion that children with LD suffer from problems with two processes of the executive system: the suppression of irrelevant information and updating.

One activity related to the central executive that has been implicated as a deficit in children with LD is their ability to suppress irrelevant infor-mation under high processing demand conditions (e.g., Chiappe, Hasher, & Siegel, 1999; De Beni, Palladino, Pazzaglia, & Cornoldi, 1998; Swanson & Cochran, 1991). These studies have investigated whether children with LD had greater trade-offs and weaker inhibition strategies than aver-age achievers on divided attention tasks. For example, Swanson designed three experiments to reflect attentional demands on both the verbal and visual-spatial system. In one of the experiments (Swanson, 1993b, Exp. 1), a concurrent memory task, adapted from Baddeley (Baddeley, Eldridge,

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Lewis, & Thomas, 1984) was administered to LD and skilled readers. The task required subjects to remember digit strings (e.g., 9, 4, 1, 7, 5, 2) while they concurrently sorted blank cards, cards with pictures of nonverbal shapes, and cards with pictures of items that fit into semantic categories (e.g., vehicles—car, bus, truck; clothing—dress, socks, belt). Demands on the central executive capacity system were manipulated through the level of difficulty (three vs. six digit strings) and type of sorting required (e.g., nonverbal shapes, semantic categories, blank cards). The results showed that readers with LD could perform comparably to chronological age (CA)-matched peers on verbal and visual-spatial sorting conditions that involved low demands (i.e., three digit strings), and that only when the coordina-tion of tasks became more difficult (e.g., six digit strings) did ability group differences emerge. More important, the results for the high memory load condition indicated less recall for readers with LD than for CA-matched (and achievement-matched) peers during both verbal and nonverbal sort-ing. Because recall performance was not restricted to a particular stor-age system (i.e., verbal storage), one can infer that processes other than a language-specific system accounted for the results.

Several studies (e.g., Swanson, 1994, 1993a,b; Swanson & Ashbaker, 2000; Swanson, Ashbaker, & Lee, 1996; Swanson & Sachse-Lee, 2001b) on executive processing have focused on updating. Updating requires moni-toring and coding of information for relevance to the task at hand, and then appropriately revising items held in WM. Thus, studies have included tasks that follow the format of Daneman and Carpenter’s Sentence Span measure, a task strongly related to student achievement (see Daneman & Merikle, 1996, for a review) that requires simultaneous juggling of stor-age and processing requirements. For example, in the reading span task by Daneman and Carpenter (1980), participants are required to read sen-tences and verify their truthfulness (processing requirement) while trying to remember the last word of each sentence (storage requirement). These studies have consistently found LD readers to be more deficient than skilled readers in WM performance using this task format, which taps cen-tral executive processes related to updating (Miyake, Friedman, Emerson, Witzki, & Howerter, 2000).

In general, a number of studies show that some participants with LD matched to NLD participants on IQ are deficient on tasks that measure specific components of executive processing. For example, a cross-sectional study (Swanson, 2003) compared skilled readers and LD readers across four age groups (7, 10, 13, 20) on phonological, semantic and visual-spatial

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WM measures administered under conditions referred to in Swanson et al. (1996): initial (no probes or cues), gain (cues that bring performance to an asymptotic level), and maintenance conditions (asymptotic conditions without cues). The results clearly showed that the LD readers had less WM recall than skilled readers for all task conditions, tasks that involved the processing of phonological, visual-spatial, and semantic information. Further, the study provided no evidence that LD readers’ WM skills “catch up” with skilled readers as they age, suggesting that a deficit model rather than a developmental lag model best captures such readers’ age-related performance. Further studies (Swanson, 1992, 1993b; Swanson et al., 1996) have found evidence of domain general processing deficits in children and adults with LD, suggestive of executive system involvement.

Those components of the executive system deficient in individu-als with LD are related to updating (e.g., Siegel & Ryan, 1989; Swanson, Ashbaker & Lee, 1996) and the inhibition of irrelevant responses (e.g., Chiappe, Hasher, & Siegel, 2000; Carretti et al., 2009). Some alternative explanations to these findings on executive processing (Swanson, 2001a,b), for example that deficits are due to ADHD, domain specific knowledge, and/or low-order processes (such as phonological coding), have been addressed elsewhere (see Swanson, 2005, 2011; for a review of studies).

Phonological LoopIn Baddeley and Logie’s model (1999), the phonological loop is special-ized for the retention of verbal information over short periods of time. It is composed of both a phonological store, which holds information in phonological form, and a rehearsal process, which serves to main-tain representations in the phonological store (see Baddeley, Gathercole, & Papagno, 1998, for an extensive review). Thus, the ability to retain and access phonological representations has been associated with verbal STM—but more specifically the phonological loop. The phonological loop has been referred to as STM because it involves two major com-ponents discussed in the STM literature: a speech-based phonological input store and a rehearsal process (see Baddeley, 1986, for review). Thus, although phonological loop is viewed as a component of Baddeley mul-tiple component model, its activities and functions fit our previous discus-sion on STM.

A substantial number of studies support the notion that children with RD experience deficits in phonological processing (e.g., see Stanovich & Siegel, 1994), such as forming or accessing phonological representations

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of information. This difficulty in forming and accessing phonological representations impairs their ability to retrieve verbal information from STM.

In general, several studies suggest that difficulties in forming and access-ing phonological representations impair the ability to learn new words in individuals with RD. A recent quantitative synthesis (Swanson, Zheng, & Jerman, 2009) shows that deficits in STM emerge across a host of measures. Our analysis shows that these deficits are primarily related to verbal infor-mation (also see O’Shaughnessy & Swanson, 1998, for an earlier synthesis) and persist across age.

Visual-Spatial Sketch PadThe visual-spatial sketch pad is specialized for the processing and storage of visual material, spatial material, or both, and for linguistic information that can be recoded into imaginable forms (see Baddeley, 1986, 2007, for a review). Measures of visual-spatial WM have primarily focused on mem-ory for visual patterns (e.g., Logie, 1986). A major study by Gathercole and Pickering (2000a,b) found that visual-spatial WM abilities, as well as mea-sures of central executive processing, were associated with attainment lev-els on a national curriculum for children aged 6 to 7 years. Children who showed marked deficits in curriculum attainment also showed marked deficits in visual-spatial WM.

Thus, there is a strong relationship between visual-spatial WM and aca-demic performance in the younger grades. However, the literature linking RD to visual-spatial memory deficits is mixed. For example, as described earlier, several studies in the STM literature suggest RD children’s visual STM is intact (see O’Shaughnessy & Swanson, 1998, for a comprehen-sive review). When visual-spatial WM (combined storage and processing demands) performance is considered, however, while some studies, again, find that visual-spatial WM in students with RD is intact when compared with their same age counterparts (e.g., Swanson, Ashbaker, & Lee, 1996, Exp. 1), others suggest problems in various visual-spatial tasks (Swanson et al., 1996, Exp. 2). Most studies suggest, however, that depending on the type of academic disability, greater problems in performance are more likely to occur on verbal than visual-spatial WM tasks.

We found that the evidence on whether children with RD have any particular advantage on visual-spatial WM when compared to their nor-mal achieving counterparts fluctuates with processing demands. Swanson (2000) proposed a model that may account for these mixed findings. There are two parts to this model. The first part of the model assumes that

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executive processes (domain general system) are used to maintain associ-ations across high demand processing conditions. A child with a reading disability has difficulty efficiently maintaining these associations. The pre-dictions of the first part of the model are consistent with current models of executive functions that are called into play only when the activities of multiple components of the cognitive architecture must be coordi-nated (e.g., Baddeley, 1996; Engle, Cantor, & Carullo, 1992). The second part of the model assumes that when excessive demands are not made on the executive system, performance differences between children with RD and without RD are limited to the verbal system. The second part of the model is consistent with earlier work suggesting that the visual-spatial system of RD readers is generally intact, but when excessive demands are placed on the executive system, their visual-spatial performance is depressed compared with chronological age-matched readers (Swanson et al., 1996). Taken together, there is evidence that children with RD (and to some degree MD) have problems in various components of the WM system.

EVERYDAY MEMORY

Although a consistent finding in the literature is that children with LD suffer deficiencies on verbal memory tasks as well as complex tasks that exceed the processing capacity of WM, conclusions are open to question because most of the findings are related to laboratory tasks. Thus, we have little understanding of how the memory of children and adults with LD operates in everyday life. Only two studies were identified in the memory literature that linked laboratory measures of memory to everyday cogni-tion in children with LD.

Swanson, Reffel, and Trahan (1991) assessed naturalistic memory of 10-year-old children with LD in three experiments. In Experiment 1, readers with and without LD were compared on their recall of com-mon objects and events, such as the name of their kindergarten teacher, items on a telephone and a penny, as well as information related to the 1986 space shuttle disaster. (These children had watched the Space Shuttle Disaster 2 years earlier on television in a classroom setting.) Also studied, via questionnaire, was the relationship between the children’s memory and their strategies for recalling activities of their daily life.

There were three important findings when the ability groups were compared. First, recall differences on the coin task (recalling information

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on a penny) indicated that children with LD were poorer than skilled readers in their recall of common visual and verbal information. Second, children with LD were less likely to remember facts about a consequen-tial event (e.g., date of the space shuttle disaster) or facts that include their earlier experiences in school (e.g., name of their kindergarten teacher). Finally, the results from the questionnaire suggested that LD readers were less likely to report using an external memory aid (e.g., write a note to themselves) so they would remember information than skilled readers.

A more recent study by McNamara and Wong (2003) compared 11-year-old children with and without LD on their recall of complex aca-demic information and information encountered in children’s everyday lives. As the researchers were interested in WM, children with LD were screened to include those with poor verbal WM skills. The academic recall measures included a sentence listening span test, a rhyming words WM test, and a visual matrix WM task. The everyday WM tasks included recall of an experienced event (a dance workshop), recall of an everyday proce-dure (checking a book out of the school library), and recall of common objects (information on the face of a coin, the components of a telephone, and the features of a McDonald’s sign). Additionally, children’s cued recall of all the tasks was measured. Compared to children without LD, those children with LD performed poorly on both the academic recall tasks as well as the everyday recall tasks. Results support the notion that some stu-dents with LD may have WM problems that affect their performance on tasks beyond reading. Further, results of the cued recall condition showed that the availability of cues decreased significantly the ability group dif-ferences on many of the academic and everyday tasks. Taken together, the results of this type of research suggest that memory deficits in children with LD are pervasive across everyday and laboratory measures.

MEMORY INTERVENTION

Based on this extensive literature on memory function in children and adults with LD, some very practical concepts and principles from memory research can serve as guidelines for instruction. We can assume that effec-tive instruction must entail information (a) about a number of strategies; (b) about how to control and implement those strategies; and (c) about the importance of effort and personal causality in producing successful performance. Furthermore, any of these components taught in isolation is likely to have diminished value in the classroom context. The following

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section describes eight major principles that must be considered if strategy instruction is to be successful (also see Montague, 1993; for further appli-cation of these principles).

Memory Strategies Serve Different PurposesOne analysis of the memory strategy research suggests there is no single best strategy for children with LD. A number of studies, for example, have looked at enhancing these children’s performance by using advanced orga-nizers, skimming, questioning, taking notes, summarizing, and so on. But apart from the fact that students with LD have been exposed to various types of strategies, the questions of which strategies are the most effective is not known. We know in some situations, such as remembering facts, the key word approach appears to be more effective than direct instruction models (Scruggs & Mastropieri, 2000), but, of course, the rank ordering of different strategies changes in reference to the different types of learn-ing outcomes expected. For example, certain strategies are better suited to enhancing students’ understanding of what they previously read, whereas other strategies are better suited to enhancing students’ memory of words or facts. The point is that different strategies can affect different cognitive outcomes in a number of ways.

Good Memory Strategies for NLD Students are not Necessarily Good Strategies for Students with LD and Vice VersaStrategies that enhance access to knowledge for normally developing stu-dents will not be well suited for all children with LD. For example, Wong and Jones (1982) trained LD and NLD adolescents in a self-questioning strategy to monitor reading comprehension. Results indicated that although the strategy training benefited the adolescents with LD, it actu-ally lowered the performance of NLD adolescents. To illustrate this point further, Swanson (1989) presented students with LD, intellectual disabili-ties, giftedness, and average development a series of tasks that involved base and elaborative sentences. Their task was to recall words embedded in a sentence. The results of the first experiment suggested that children with LD differ from the other groups in their ability to benefit from elabora-tion. That is, while the other groups clearly benefited from the elaborative when compared to the base sentence condition, there was no clear advan-tage for either type of sentence for participants with LD. In sum, these results suggest that strategies that are effective for NLD students may be less effective for students with LD.

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Effective Memory Strategies do not Necessarily Eliminate Processing DifferencesIt appears logical that if children with LD use a strategy that allows them to process information efficiently, then improvement in performance is due to the strategies’ affecting the same processes that they do in NLD students. This assumption has emanated primarily from studies that have imposed organization on seemingly unorganized material. For example, considerable evidence indicates that readers with LD do not initially take advantage of the organizational features of material (e.g., Lee & Obrzut, 1994). However, the notion that readers with disabilities process the orga-nizational features of information in the same manner as NLD students is questionable (Swanson, 1986). For example, Swanson and Rathgerber (1986) found in categorization tasks that readers with disabilities can retrieve information without interrelating superordinate, subordinate, and coordinate classes of information, as the NLD children do. Thus, chil-dren with LD can learn to process information in an organizational sense without knowing the meaning of the material. The point is that simply because children with LD are sensitized to internal structure of material via some strategy (e.g., by cognitive strategies that require the sorting of material) it does not mean they will make use of the material in a manner consistent with what was intended from the instructional strategy.

The Strategies Taught are not Necessarily the Ones UsedThe previous principle suggests that during intervention different pro-cesses may be activated that are not necessarily the intent of the instruc-tional intervention. It is also likely that students with disabilities use different strategies on tasks in which they seem to have little difficulty and these tasks will likely be overlooked by the teacher for possible interven-tion. It is commonly assumed that although students with LD may have isolated memory deficits (verbal domain) and require general learning strategies to compensate for these processing deficits, their processing of information is comparable with that of their normal counterparts on tasks with which they have little trouble. Several authors suggest, however, that there are a number of alternative ways for achieving successful perfor-mance, and some indirect evidence indicates that students with LD may use qualitatively different mental operations (Shankweiler et al., 1979) and processing routes (e.g., Swanson, 1988) from their NLD counterparts.

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Memory Strategies in Relation to a Student’s Knowledge Base and CapacityOne important variable that has been overlooked in the LD intervention literature is the notion of processing constraints. Memory capacity seems to increase with development, with a number of factors potentially con-tributing to the overall effect. STM capacity increases with age (Case, Kurland, & Goldberg, 1982). A number of component processes increase in speed with development, with faster processes generally consuming less effort than slow processes and thus the same amount of capacity can seem greater (i.e., there is a functional increase of capacity with increasing effi-ciency of processing). Older children are likely to have more organized prior knowledge which can reduce total number of chunks of informa-tion that are processed and decrease the amount of effort to retrieve infor-mation from LTM. These developmental relationships may play a role in strategy effectiveness. To test this possibility, Pressley, Cariglia-Bull, and Schneider (1987) studied children’s ability to execute a capacity demand-ing imagery representation strategy for the learning of sentences. Children in an experimental condition were presented a series of highly concrete sentences (e.g., the angry bird shouted at the white dog, the turkey pecked the coat). They were asked to imagine the meanings of these sentences. Control condition participants were given no instruction. Children ben-efited from imagery instruction. However, performance depended on the child’s functional STM capacity, as reflected by individual differences in performance on classic memory span task. That is, the imagery versus con-trol difference in performance was only detected when functional STM was relatively high.

Comparable Memory Strategy May not Eliminate Performance DifferencesSeveral studies earlier have indicated that residual differences remain between ability groups even when ability groups are instructed and/or prevented from strategy use. For example, in a study by Gelzheiser et al. (1987), discussed earlier, children with and without LD were compared on their ability to use organizational strategies. After instruction in orga-nizational strategies, the two groups were compared on their abilities to recall information on a posttest. The results indicated that children with LD were comparable in strategy use to NLD children, but were deficient in overall performance.

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Memory Strategies Taught do not Necessarily become Transformed into Expert StrategiesChildren who become experts at certain tasks often have learned simple strategies and, through practice, discover ways to modify them into more efficient and powerful procedures. In particular, the proficient learner uses higher-order rules to eliminate unnecessary or redundant steps to hold increasing amounts of information. A child with LD, in contrast, may learn most of the skills related to performing an academic task and per-form appropriately on that task by carefully and systematically following prescribed rules or strategies. Although children with LD can be taught strategies, some studies suggest that the difference between NLD (experts in this case) and children with LD is that the former have modified such strategies to become more efficient (Swanson & Cooney, 1985). It is plau-sible that a child with LD remains a novice in learning new information because he or she fails to transform memory strategies into more efficient forms (see Swanson & Rhine, 1985).

Strategy Instruction Must Operate on the Law of ParsimonyA number of multiple-component packages of strategy instruction have been suggested for improving LD children’s functioning. These compo-nents have usually encompassed some of the following: skimming, imagin-ing, drawing, elaborating, paraphrasing, using mnemonics, accessing prior knowledge, reviewing, orienting to critical features, and so on. No doubt there are some positive aspects to these strategy packages in that:1. These programs are an improvement over some of the strategies seen

in LD literature to be rather simple or ‘quick-fix’ strategies (e.g., rehearsal or categorization to improve performances).

2. These programs promote a domain skill and have a certain metacogni-tive embellishment about them.

3. The best of these programs involve (a) teaching a few strategies well rather than superficially; (b) teaching students to monitor their perfor-mance; (c) teaching students when and where to use the strategy to enhance generalization; (d) teaching strategies as an integrated part of an existing curriculum; and (e) teaching that includes a great deal of supervised student practice and feedback.

The difficulty of such strategy packages, however, at least in terms of theory, is that little is known about which components best predict stu-dent performance, nor do they readily permit one to determine why the

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strategy worked. The multiple-component approaches that are typically found in a number of strategy intervention studies must be carefully con-trasted with a component analysis approach that involves the systematic combination of instructional components known to have an additive effect on performance.

Training WM DirectlyBefore leaving research linking performance instruction to memory, there is a question as to whether WM can be trained directly. As reviewed, most memory training interventions for children focus on teaching mem-ory strategies (e.g., keyword method, rehearsal, clustering, elaboration). However, the effects of these training studies remain task specific and usu-ally are not transferable to a wide variety of classroom or academic tasks. A promising alternative towards providing strategy interventions is a process specific approach, such as WM training. With WM training, the goal is not to train additional processes in the sense of strategies, such as the mne-monics or rehearsal, but instead to train the WM system directly. In one of the few studies on the effects of training on the WM performance in children, Klingberg, Fernell, Olsen, Johnson, Gustafsson, Dahlstrom et al. (2005) found that when children with ADHD were exposed to a com-puterized WM training program that significant improvements emerged on measures of verbal and visual-spatial memory and complex reasoning (Raven Colored Progressive Matrices Test) relative to the control condi-tions. Improvements in WM and their links to reasoning were attributed to activities of the central executive system (e.g., response inhibition). However, the study did not address whether the treatment effects influ-enced academic performance.

A recent study by Swanson, Kehler and Jerman (2010) addressed the question as to whether direct strategy instruction can improve WM per-formance between children with and without reading difficulties. All chil-dren were randomly assigned clinical trials that involved rehearsal training or nontraining. Swanson et al. (2008) found that the use of rehearsal strat-egy instruction positively influenced post-test span scores on a WM task (Operation Span task). Both groups in this study (children with and with-out reading problems) benefited from strategy instruction. However, the WM gains were no greater for children with reading difficulties than chil-dren without reading problems. These findings are comparable to Engle et al. (1992) showing that strategies do not drive the relationship between WM and reading ability.

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Testing-the-Limits StudiesAnother approach to directly improving WM performance is through a dynamic testing procedure referred to as testing-the-limits. This procedure has found that performance conditions that include simple feedback and memory cues contribute unique variance to reading and math beyond tra-ditional testing conditions (e.g., Swanson, 1999a, 2003). For these studies, WM tasks were presented to the same children under three conditions: initial (no probes or cues), gain (cues that bring performance to an asymp-totic level), and maintenance conditions (asymptotic conditions without cues). Previous studies (Swanson, 1992, 1999a, 2003, 2010; Swanson et al., 1996) have shown that the gain conditions improve WM performance by as much as 1 standard deviation. This occurred because the systematic cuing procedures emphasized sequential processing strategies and thereby reduced the number of competing strategies employed. The maintenance condition allowed for the examination as to whether WM difficulties in children reflected capacity constraints in accessing what had been previ-ously stored (as well as retrieved) in the gain condition. For the main-tenance condition, the same WM tasks that matched each participant’s highest WM span level (gain score) were again administered, but without cues. The general findings across several studies (Swanson, 1992, 2003; Swanson & Howard, 2005) have been that skilled readers performed bet-ter than children with reading difficulties in all processing conditions and that concurrent reading comprehension performance was best predicted by the maintenance testing than the other WM testing conditions. Further, the magnitude of the difference (effect size) between high and low read-ers increased on gain and maintenance testing conditions when compared with the initial conditions, suggesting that the performance gap between ability groups was increased by using testing-the-limits procedures.

In general, a number of studies have shown that WM can be improved upon. In addition, simple feedback on WM performance adds significant variance with predicting academic outcomes. However, few studies have shown that WM training directly influences performance on academic measures, such as reading and math. Some studies have found some generalization to nontargeted related processes (visual WM train-ing was related to recognizing visual spatial patterns), but WM training to date has not been shown at this point to make substantial improve-ment on important classroom tasks such as reading comprehension and/or math performance.

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SUMMARY AND CONCLUSIONS

In summary, we have briefly characterized research on memory and LD. Our knowledge of the memory of individuals with LD somewhat par-allels our knowledge about the differences between older and younger children’s memory. The parallel relies in effortful processing, the focus on cognitive strategies, the development of a knowledge base, and the awareness of one’s own memory processes. Most memory research ema-nates from an information-processing framework. Earlier research tended to emphasize the integration of information across modalities (visual-auditory) and perception (visual memory), whereas more recent studies have tended to focus on the representation, control, and executive process (e.g., strategies) of memory. Current research on memory is beginning to examine the interaction of structures and process on performance. Most of the current research is occurring in the area of WM. The limitations of previous models are highlighted as well as recent trends in memory research on students with LD. A number of principles related to mem-ory strategy instruction have emerged that have direct application to the instruction of children and adults with LD. Some of these principles are related to the purposes of strategies, parsimony with regard to the number of processes, individual differences in strategy use and performance, learner constraints, and the transfer of strategies into more efficient processes.

The important conclusion from this review is that children and adults with LD, who have normal intelligence but experience difficulties in spe-cific academic areas (e.g., reading, math), suffer memory difficulties. These memory difficulties are not pervasive but are related to two components of working memory: the phonological loop and the executive system. The phonological loop specializes in the retention of speech-based informa-tion. The research also finds that situations that place high demands on processing (e.g., comprehension), which in turn exert demands on con-trolled attentional processing (such as monitoring limited resources, sup-pressing conflicting information, updating information), place children and adults with LD at a clear disadvantage when compared with their chron-ological aged counterparts. Children and adults with LD executive pro-cessing difficulties may include (a) maintaining task relevant information in the face of distraction or interference; and (b) suppressing and inhibit-ing information irrelevant to the task if necessary. We also find evidence that the WM of children and adults with LD can be improved (i.e., with dynamic testing).

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