What develops in working memory? A life span perspective.

This study investigated whether working-memory (WM) span differences across age are attributable to specific or general processing functions. The study compared 9 age groups (6, 8, 10, 13, 16, 24, 35, 45, 57 years) on verbal and visuospatial WM performance under initial (no probes or cues), gain (cues that bring performance to an asymptotic level), and maintenance conditions (asymptotic conditions without cues). (a) Age-related performance differences in WM were found across all conditions and were not isolated to specific processes, (b) significant performance differences remained among age groups on gain and maintenance conditions, and (c) the gain (accessing new information) and maintenance conditions (maintenance of old information) for verbal and visuospatial WM tasks contributed independent variance to age-related performance. The results support a general capacity explanation of age-related differences. These differences in capacity reflect demands placed on both the accessing of new information and the maintenance of old information.

Learning disabilities, distinctive encoding, and hemispheric resources.

The purpose of this study was to isolate possible sources of learning ability differences in distinctive encoding of item-specific and relational information. Two mechanisms postulated as underlying ability group differences were attentional capacity (as inferred from the magnitude and direction of correlations between primary and secondary recall) and resource monitoring strategies (as reflected in measures of selective attention and laterality). In Experiment 1, learning disabled and nondisabled childrens' word recall was compared on dichotic listening recall tasks that included nonorienting instructions, and orienting instructions that directed children's attention toward semantic, phonemic, or structural word features. Disabled children showed lower recall and more diffuse selective attention to word features than nondisabled children. Reciprocity (negative correlations) between targeted and background words within and between ability groups was comparable, except when targeted word features were phonemically organized. Experiment 2 indicated that disabled childrens' cued recall was inferior to that of nondisabled children, even though both ability groups produced comparable symmetrical recall patterns related to ear presentations. Taken together, the results suggest that the locus of disabled childrens' distinctive encoding deficiencies is related to resource monitoring strategies during interhemispheric processing.

Developmental recall lag in learning-disabled children: perceptual deficit or verbal mediation deficiency?

To investigate the development of mediational deficiencies in verbal and nonverbal visual short-term memory of learning-disabled children, the recall task of Atkinson, Hansen, and Bernback was administered to learning-disabled children in two experimental conditions. In Experiment 1 no significant differences on nonverbal short-term memory recall between normal and learning-disabled children were found. Similar recall responses (e.g., middle response bias, primacy effects, and recency effects) were found for both groups. Nonverbal recall was comparable for disabled and normal children as suggested by stimulus content and association scores. Experiment 2 found that while the effects of overt rehearsal on pretrained labels on learning-disabled children's recall was negligible, labels provided superior recall for normal children. Results suggested that learning-disabled children suffer from a verbal mediational deficiency consistent with Flavell's (1970) mediation deficiency hypothesis.

What learning-disabled readers fail to retrieve on verbal dichotic tests: a problem of encoding, retrieval, or storage?

Three theoretical models were assessed as a framework for capturing learning-disabled readers' faulty word retrieval. To this end, learning-disabled and skilled readers were compared on verbal dichotic listening tasks for free recall and cued recall of word lists organized by semantic, phonemic, and structural features. The results indicated that disabled readers were comparable on free recall but were inferior to skilled readers on cued recall. No ability group differences were found for categorical and noncategorical recall intrusions during the cued recall phase. Cued recall performance was further analyzed for individual differences in memory trace structure (via the Tulving & Watkins, 1975, reduction method), ear asymmetry, and the allocation of attention to word features prior to cuing. Results indicated that during the cued recall phase, disabled readers' memory traces were inferior in structure to those of skilled readers, even though the two ability groups produced comparable symmetrical recall patterns for the ear presentations. Further, disabled readers had lower selective attention scores for the interhemispheric processing of information prior to cuing than did skilled readers. Taken together, the results suggest that, prior to cued recall, disabled readers suffer from attentional difficulties during interhemispheric processing, which in turn influences the structural formation of their memory trace.

Executive processing differences between learning-disabled, mildly retarded, and normal achieving children.

This study examined possible executive processing differences between mildly retarded, learning-disabled, and normal achieving children. To this end, the groups were compared as to their ability to recall central and secondary words from base and elaborative sentences under conditions of high and low encoding effort. Executive processing was inferred from the children's ability to maintain optimal recall performance for central and secondary words. Groups were comparable in central recall, but differences in secondary recall occurred for the high-effort encoding condition. Qualitative differences related to the prioritizing of resources (as reflected in the correlation between central and secondary recall) and monitoring the transfer of information (as reflected from central and secondary recall insertions) were found between groups. The results were discussed in terms of an executive processing framework that views retarded children as suffering from inefficiencies related to the sharing of resources, whereas the learning-disabled children's inefficiencies were related to the discrimination of resources.

A developmental study of vigilance in learning-disabled and nondisabled children.

To test the proposition that learning-disabled children manifest a sustained attentional deficit, the Continuous Performance Test was administered to learning-disabled and nondisabled children at three age levels. Children were tested on three task lengths (5, 10, and 15 minutes) and two modalities (auditory and visual) in which dependent measures were correct detections and false responses, d' and B values. As expected, learning-disabled children male fewer correct detections and more false responses and were less sensitive (d') to critical stimuli than were nondisabled children at all ages. There was also evidence to indicate that learning-disabled children apply different response criteria across age when compared to nondisabled children. B values varied significantly across age, group, modality, and time on task; d' remained relatively unchanged across time periods. The popular notion that learning-disabled and younger subjects start a vigilance task with the same capacity as nondisabled older children but show a decline in attention as time on task increases was not supported.

The relationship between intelligence and vigilance in children at risk.

The purpose of this study was to compare two competing models as an explanation of the relationship between intelligence and sustained attention in educationally at-risk kindergarten children. One model assumes that lower-IQ subjects allocate greater amounts of attentional resource of information-processing tasks than higher-IQ subjects, whereas the other model assumes that a "less-than" optimal level of arousal is associated with decrements in task performance across time. Twenty-nine teacher-nominated at-risk and 29 normal achieving kindergarten students were administered the Wechsler Preschool and Primary Scale of Intelligence-Revised (WPPSI-R) and vigilance taks. Signal detection measures of stimulus detectability (d'), decision criterion (beta), correct detections, and false alarms were used to assess children's sustained attention across three time periods (2, 4, and 6 min). The important results were (a) high-risk children were inferior on d' measures when compared to normal achieving children, (b) vigilance measures did not vary over time in either group, and (c) intelligence and vigilance shared a common factor in high-risk, but not low-risk, children. The results suggest that children educationally at risk suffer deficits related to attentional capacity for processing information.

Naturalistic memory in learning-disabled and skilled readers.

Three experiments compared learning-disabled and skilled readers' performance on naturalistic memory measures, as well as investigated the relationship between memory performance on everyday and laboratory tasks. In Experiment 1, the laboratory task (sentence span task) and everyday memory measures were correlated moderately for both ability groups. Compared to skilled readers, disabled readers performed poorly on the sentence span task, and were less likely than skilled readers to remember information related to common objects and consequential events. Disabled readers were also less likely to rely on external prompts to help them recall everyday information. Experiment 2 extended the previous findings to older subjects and found that the majority of significant correlations between the laboratory (word span task) and everyday memory tasks were isolated to disabled readers. When compared to chronological-age-matched subjects, disabled readers were inferior in recency performance on the laboratory (word span) and natural serial recall (e.g., recall of U.S. presidents) tasks. Experiment 3 showed that under conditions that facilitate item accessibility, ability group differences in recall were comparable. Taken together, the findings indicate that disabled readers' memory deficits are pervasive across naturalistic and laboratory measures at the younger age, but these deficits diminish for older students. Further, the deficits that occur at the older age are due to problems in accessing knowledge.

Working memory in skilled and less skilled readers.

This study assessed skilled and less skilled readers' working memory performance. Fifty skilled and less skilled readers at two age levels were presented with sentence span and concurrent memory tasks. The span task results indicated that working memory differences exist between reading groups. The concurrent task revealed performance deficits for less skilled readers across verbal and nonverbal conditions, suggesting a central processing deficiency. Age differences were isolated to skilled readers. It was concluded that less skilled readers' working memory deficiencies were pervasive in the sense that they involve deficiencies in memory components related to central executive processing.

A case of Peters' anomaly in a springer spaniel.

An 8-week-old springer spaniel presented with a large central corneal opacity of the left globe, which was accompanied by cords of tissue spanning from the iris collarette to the posterior cornea. A posterior cortical cataract was noted in the right eye. At the owner's request the puppy was humanely destroyed, and a necropsy was performed. Upon sectioning the left globe in the vertical plane, a circle of pigmented strands of tissue was observed spanning the anterior chamber from the iris to the posterior aspect of the cornea. The right globe appeared normal when inspected grossly. Histologically, a membrane of pigmented tissue covered the posterior aspect of the broad central corneal leukoma of the left globe. This membrane and the cords traversing the anterior chamber were composed of vascular uveal tissue. Descemet's membrane and the corneal endothelium were reduced or absent in the zone of corneal opacity. Other than the changes associated with cataract, the right globe was histologically normal. The clinical and histological findings in the left globe were identical with those described for Peters>> anomaly in human beings.

Are working memory deficits in readers with learning disabilities hard to change?

This study investigated whether changes in the working memory (WM) performance of readers with learning disabilities (LD) is related to a general or domain-specific system. The study compared readers with LD, chronologically age-matched (CA-M), and reading level-matched (RL-M) children's WM performance for phonological, visual-spatial, and semantic information under initial (no probes or cues), gain (cues that bring performance to an asymptotic level), and maintenance (asymptotic conditions without cues) conditions. The main findings indicated that (a) CA-M children were superior in performance to readers with LD across initial, gain, and maintenance conditions, (b) readers with LD showed less change (as reflected in effect size scores, slopes for the quadratic curve) on both visual-spatial and verbal (phonological and semantic) WM tasks across gain and maintenance conditions than the CA-matched children, and (c) the performance of readers with LD was superior to the RL-M children's performance on initial conditions, but inferior on gain and maintenance conditions. Taken together, the results suggest that a general system moderated the changes in retrieval of phonological, visual-spatial, and semantic information in readers with LD.

Short-term memory and working memory: do both contribute to our understanding of academic achievement in children and adults with learning disabilities?

Seventy-five children and adults with learning disabilities (age range = 5.0 to 42.10 yrs.) and 86 normally achieving children and adults (age range = 5.11 to 58.0 yrs.) were compared on short-term memory (STM) and working memory (WM) tasks to assess the relationship between STM and WM, and to test whether these measures independently relate to achievement. For both ability groups, the factor analyses indicated that STM and WM loaded on different factors, and the regressions and partial correlations showed that these different factors accounted for separate variance in reading comprehension and mathematics. Both STM and WM are important in understanding reading comprehension and mathematics performance in children and adults with learning disabilities; however, WM is more important for children and adults without learning disabilities. In contrast to WM, STM contributed minimal variance to word recognition in both ability groups. Overall, it was concluded that STM and WM do reflect different processes, both of which seem to separate the two ability groups. However, models of memory that view STM and WM as interchangeable, or STM in isolation, do not provide an adequate framework for capturing academic performance in children and adults with learning disabilities.

Reading research for students with LD: a meta-analysis of intervention outcomes.

The present article provides a meta-analysis of instructional research with samples of children and adolescents with learning disabilities in the domains of word recognition and reading comprehension. The results of the synthesis showed that a prototypical intervention study has an effect size (ES) of .59 for word recognition and .72 for reading comprehension. Four important findings emerged from the synthesis: (a) Effect sizes for measures of comprehension were higher when studies included derivatives of both cognitive and direct instruction, whereas effect sizes were higher for word recognition when studies included direct instruction; (b) effect sizes related to reading comprehension were more susceptible to methodological variation than studies of word recognition; (c) the magnitude of ES for word recognition studies was significantly related to samples defined by cutoff scores (IQ > 85 and reading < 25th percentile), whereas the magnitude of ES for reading comprehension studies was sensitive to discrepancies between IQ and reading when compared to competing definitional criteria; and (d) instructional components related to word segmentation did not enter significantly into a weighted least square hierarchical regression analysis for predicting ES estimates of word recognition beyond an instructional core model, whereas small-group interactive instruction and strategy cuing contributed significant variance beyond a core model to ES estimates of reading comprehension. Implications related to definition and instructional components that optimize the magnitude of outcomes are discussed.

A meta-analysis of single-subject-design intervention research for students with LD.

This article summarizes single-subject-design intervention studies that include students with learning disabilities. Effect sizes of 85 studies were analyzed across instructional domains (e.g., reading, mathematics); sample characteristics (e.g., age, intelligence); intervention parameters (e.g., number of instructional sessions, instructional components); and methodological procedures (e.g., internal validity, treatment integrity, sample representation). The major findings were as follows: (a) All domain areas except handwriting yielded effect sizes at or above Cohen's .80 threshold for a substantial finding; (b) instructional components related to drill-repetition-practice-review, segmentation, small interactive groups, and the implementation of cues to use strategies contributed significant variance (15%) to estimates of effect size; (c) strategy instruction (SI) models better predicted effect size estimates than direct instruction (DI) models when the results were qualified by the reported intellectual and reading levels of the participants; (d) high-IQ discrepancy groups yielded lower effect sizes compared to low-IQ discrepancy groups in the domain of reading, whereas the reverse effect occurred when treatment outcomes were not reading measures; and (e) the low-IQ discrepancy groups yielded higher effect sizes for a Combined DI and SI Model when compared to competing models. The results are supportive of the pervasive influence of cognitive strategy and direct instruction models across treatment domains and of the notion that variations in sample definition moderate treatment outcomes.

The relationship between phonological codes on memory and spelling tasks for students with and without learning disabilities.

The purpose of the study was to determine the degree to which 31 (23 boys and 8 girls) 13-year-old children with learning disabilities from Grades 7, 8, and 9 were comparable to younger (9-year-old) reading- and spelling-matched controls in (a) phonological similarity effects, (b) phonetically based misspellings, and (c) relationships between memory and spelling performance. Children with reading disabilities and reading-recognition-matched controls, subgrouped by spelling ability, were compared on their memory for phonetically similar and dissimilar word lists and types of spelling errors. The results indicate that children with reading disabilities who are matched to younger children on both reading recognition and spelling ability exhibit normal phonological effects on memory and spelling measures. Within each reading group, low spellers produced more semiphonetic errors than high spellers, and high spellers produced more phonetic errors than low spellers. Significant correlations between memory and spelling error measures were more frequent for children with reading disabilities when compared to controls matched on reading and spelling ability. It was concluded that the phonological performance of reading/spelling-matched children with reading disabilities is characterized by an overreliance on phonological codes, whereas their counterparts' performance reflects independent and less generalizable use of phonological substrates across tasks.

Treatment outcomes for students with learning disabilities: how important are internal and external validity?

This study analyzed the magnitude of experimental intervention outcomes as a function of violations in internal and external validity for studies that included students with learning disabilities. The results indicated that treatment outcomes were significantly affected by the following violations: teacher effects, establishing criterion levels of instructional performance, reliance on experimental measures, using different measures between pretest and posttest, using a sample heterogenous in age, and using incorrect units of analysis. Furthermore, the underreporting of information related to ethnicity, locale of the study, psychometric data, and teacher applications positively inflated the magnitude of treatment outcomes. A weighted hierarchical regression analysis revealed that composite scores of the aforementioned high-risk variables accounted for 16% of the total variance in effect size. The implications for interpreting intervention research to practice are discussed.

Are mathematics disabilities due to a domain-general or a domain-specific working memory deficit?

The relationship between verbal and visual-spatial working memory and mathematical computation skill was examined in children and adults with and without disabilities in mathematics. A hierarchical regression analysis showed that, when partialing for the influence of reading ability, age, and gender, mathematical computation was better predicted by verbal than by visual-spatial working memory. Furthermore, the results showed that the relationship between mathematics ability and working memory were not significantly moderated by age but were stable across a broad age span. We concluded that, regardless of age, deficits in mathematics are mediated by both a domain-general and a domain-specific working memory system.

A subgroup analysis of working memory in children with reading disabilities: domain-general or domain-specific deficiency?

The purpose of this study was to investigate whether changes in working memory (WM) of children with reading disabilities (RD) were related to a domain-specific or a domain-general system. Based on Daneman and Carpenter's (1980) Sentence Listening Span task, children were subgrouped into a group of high executive processing (high listening span) children without RD, a group of low executive processing (low listening span) children with RD, and a group of children with and without RD matched on executive processing (moderate listening span). Subgroups were compared on phonological, visual-spatial, and semantic WM tasks across initial (no probes or cues), gain (cues that bring performance to an asymptotic level), and maintenance conditions (asymptotic conditions without cues). The results showed that (a) children without RD high in executive processing ability outperformed all other subgroups, (b) the RD subgroup low in executive processing performed poorly relative to all other subgroups across task and memory conditions, (c) children with and without RD matched on executive processing were comparable in WM span and changes in WM for all tasks, and (d) WM performance of children with RD was a strong linear function of the high executive processing group, suggesting that the nature or the specific componential makeup of the tasks are not the main contributors to WM performance. Taken together, the results suggest that a domain-general system may partially contribute to poor WM in children with RD, and that this system may operate independently of their reading deficits.

Does strategy knowledge influence working memory in children with mathematical disabilities?

This study investigated the relationship between working memory (WM), declarative strategy knowledge, and math achievement in children with and without mathematical disabilities (MD). Experiment 1 examined the relationship between strategy knowledge, verbal WM, and visual-spatial WM in children with MD as a function of initial, gain, and maintenance conditions. The results showed that after partialing the influence of reading, stable strategy choices rather than specific strategy knowledge was related to verbal and visual-spatial WM span in high demand (maintenance) conditions. Experiment 2 compared children with MD to a group of chronological age-matched children and a group of math ability-matched children on the same conditions as Experiment 1. Age-matched children's verbal and visual-spatial WM performance was superior to that of children with MD, whereas WM performance was statistically comparable between children with MD and younger children matched on math ability. The selection of expert strategies was related to high WM span scores in the initial conditions. After controlling for reading achievement in a regression analysis, verbal and visual-spatial WM, stable verbal strategy choices, and expert strategy choices related to visual-spatial processing all contributed independent variance to math achievement. Overall, these results suggest that WM and math achievement are related to strategy knowledge.

A comparison of two reading interventions for children with reading disabilities.

This study compared the effectiveness of two reading interventions in a public school setting. Forty-five second-grade children with reading disabilities were randomly assigned to a 6-week phonological awareness, word analogy, or math-training program. The two reading interventions differed from each other in (a) the unit of word analysis (phoneme versus onset-rime), (b) the approach to intervention (contextualized versus decontextualized), and (c) the primary domain of reading instruction (oral versus written language). Results indicate that children in both reading programs achieved significant gains in beginning reading skills, learning the specific skills taught in their respective programs, and applying what they had learned to uninstructed material on several transfer-of-learning measures, in comparison to children in the control group. For children in both reading intervention groups, the most significant mediator of growth in oral reading fluency was a child's initial level of word identification skill. Implications of these findings are that systematic, high quality reading intervention can occur in a small group, public school setting and that there are several different paths to the remediation of children with reading disabilities.