Biomedical subjects

Jack M Fletcher

Publications and source records attributed to Jack M Fletcher.

At least 37 records · Page 2Linked to original sources

PubMed2003

Neural systems for compensation and persistence: young adult outcome of childhood reading disability.

BACKGROUND: This study examined whether and how two groups of young adults who were poor readers as children (a relatively compensated group and a group with persistent reading difficulties) differed from nonimpaired readers and if there were any factors distinguishing the compensated from persistently poor readers that might account for their different outcomes. METHODS: Using functional magnetic resonance imaging, we studied three groups of young adults, ages 18.5-22.5 years, as they read pseudowords and real words: 1) persistently poor readers (PPR; n = 24); 2) accuracy improved (compensated) readers (AIR; n = 19); and 3) nonimpaired readers (NI, n = 27). RESULTS: Compensated readers, who are accurate but not fluent, demonstrate a relative underactivation in posterior neural systems for reading located in left parietotemporal and occipitotemporal regions. Persistently poor readers, who are both not fluent and less accurate, activate posterior reading systems but engage them differently from nonimpaired readers, appearing to rely more on memory-based rather than analytic word identification strategies. CONCLUSIONS: These findings of divergent neural outcomes as young adults are both new and unexpected and suggest a neural basis for reading outcomes of compensation and persistence in adults with childhood dyslexia.

Adult↗

PubMed2003

Abnormal activation of temporoparietal language areas during phonetic analysis in children with dyslexia.

Event-related magnetic fields were recorded using magnetoencephalography in children with (n=12) and without (n=11) dyslexia while they discriminated between pairs of syllables from a voice onset time series (/ga/-/ka/). Nonimpaired readers exhibited left-hemisphere predominance of activity after the resolution of the N1m, whereas children with dyslexia experienced a sharp peak of relative activation in right temporoparietal areas between 300 and 700 ms post-stimulus onset. Increased relative activation in right temporoparietal areas was correlated with reduced performance on phonological processing measures. Results are consistent with the notion that deficits in appreciating the sound structure of both written and spoken language are associated with abnormal neurophysiological activity in temporoparietal language areas in children with dyslexia.

Child↗

PubMed2003

Auditory temporal processing in children with specific reading disability with and without attention deficit/hyperactivity disorder.

The auditory temporal deficit hypothesis predicts that children with specific reading disability (RD) will exhibit a deficit in the perception of auditory temporal cues in nonspeech stimuli. Tasks assessing perception of auditory temporal and nontemporal cues were administered to children with (a) RD without attention-deficit/hyperactivity disorder (RD/no-ADHD, n = 40), (b) ADHD alone (ADHD/no-RD, n = 33), (c) RD and ADHD (RD/ADHD, n = 36), and (d) no impairment (NI, n = 41). The presence of RD was associated with a specific deficit in detection of a tone onset time asynchrony, but no reduction in performance on other tasks assessing perception of temporal or nontemporal acoustic cues. The presence of ADHD was associated with a general reduction in performance across tasks. The pattern of results did not indicate a pervasive deficit in auditory temporal function in children with RD, but did suggest a possible sensitivity to backward masking in this group. Results also indicated that the comorbid presence of ADHD is a significant factor in the performance of children with RD on psychoacoustic tasks.

Attention Deficit Disorder with Hyperactivity↗

PubMed2003

Brain mechanisms for reading in children with and without dyslexia: a review of studies of normal development and plasticity.

In this article we review our experience with the application of magnetic source imaging (MSI), the newest of the functional imaging methods, to the study of brain mechanisms for reading among children who read normally and among those with dyslexia. After giving a general description of MSI, we present evidence for reliable and valid maps of the brain mechanism for aural language comprehension as well as for reading. Next, we present data from 39 normal readers, 40 children with dyslexia, and 30 younger children at risk for developing a reading disability. These data show different brain activation maps for individual children with dyslexia and children at risk for dyslexia than for those of normal readers. Such differences most likely reflect aberrant brain organization underlying phonological decoding, rather than variables such as degree of effort. Finally, we present preliminary data demonstrating that the aberrant activation profiles of children with dyslexia may return to normative patterns as a result of a successful reading intervention that enables children to improve phonological decoding skills.

Adolescent↗

PubMed2003

Interventions aimed at improving reading success: an evidence-based approach.

There is a consensus among researchers about the critical elements for effective reading instruction. These elements are the integration of explicit instruction in the alphabetic principle, reading for meaning, and opportunity to learn. These critical elements are present in classroom instruction that prevents reading difficulties as well as effective small-group and one-on-one interventions. Research on effective classroom instruction and reading interventions is described, and the case is argued that the most effective intervention is provided early--in kindergarten through 2nd grade--rather than after 3rd grade, and allows for sufficient intensity, duration, and supportiveness that no child is left behind. Policy implications for changes in (a) the way learning disabilities are identified and (b) the content of professional development of teachers are discussed.

Child↗

PubMed2003

Early brain injury in children: development and reorganization of cognitive function.

Children who sustain congenital or acquired brain injury typically experience a diffuse insult that impacts many areas of the brain. Yet research has only recently begun to examine the development of these children, who often provide excellent examples of the presence or absence of neural plasticity. Development and recovery after such injuries reflects both restoration and reorganization of cognitive functions. To understand these processes, research should focus on questions and assessment paradigms oriented toward the acquisition (rather than the recovery) of cognitive functions. Outcomes may appear similar across types of insults, even when the sources of difficulties and their neural correlates are different. Comparisons of outcomes involving intellectual functions, memory and learning, reading, and language/discourse in children who sustain congenital injury (spina bifida meningomyelocele) and acquired injury (traumatic brain injury) illustrate these principles and the value of research on diffuse brain injury in children.

Brain Injuries↗

PubMed2002

Effects of event probability and sequence on children with attention-deficit/hyperactivity, reading, and math disorder.

BACKGROUND: We investigated the impact of stimulus probability and sequence on performance and event-related potentials of 310 children classified into 12 combinations of attention-deficit/hyperactivity disorder (Not-attention-deficit/hyperactivity disorder, Inattentive and Combined subtypes) with presence/absence of reading disorder and math disorder. METHODS: Subjects pressed buttons to displays of the letters O and X, which were presented with probabilities of either .17/.83 or .50/.50. Greater response selection was required in the .17/.83 condition. RESULTS: Stimulus probability had comparable effects on all diagnostic groups. The extent of mismatch between a stimulus and preceding events elicited less systematic increases in errors, P3b latency, and P3b amplitude among both attention-deficit/hyperactivity disorder subtypes than controls. Mismatch with preceding trials more greatly reduced math disorder and reading disorder + math disorder children's speed in the Rare task and accuracy in both conditions. Math disorder and reading disorder + math disorder subjects also registered less the effects of alternations of the infrequent O on N2 amplitude and on P3b latency. CONCLUSIONS: Math disorder and reading disorder + math disorder youngsters' lower sensitivity to sequence irregularity in their event-related potentials along with greater disruption of performance suggest working memory deficits that adversely affected response selection. Comorbidity of attention-deficit/hyperactivity disorder and reading disorder did not affect the results.

Adolescent↗

PubMed2002

Disruption of posterior brain systems for reading in children with developmental dyslexia.

BACKGROUND: Converging evidence indicates a functional disruption in the neural systems for reading in adults with dyslexia. We examined brain activation patterns in dyslexic and nonimpaired children during pseudoword and real-word reading tasks that required phonologic analysis (i.e., tapped the problems experienced by dyslexic children in sounding out words). METHODS: We used functional magnetic resonance imaging (fMRI) to study 144 right-handed children, 70 dyslexic readers, and 74 nonimpaired readers as they read pseudowords and real words. RESULTS: Children with dyslexia demonstrated a disruption in neural systems for reading involving posterior brain regions, including parietotemporal sites and sites in the occipitotemporal area. Reading skill was positively correlated with the magnitude of activation in the left occipitotemporal region. Activation in the left and right inferior frontal gyri was greater in older compared with younger dyslexic children. CONCLUSIONS: These findings provide neurobiological evidence of an underlying disruption in the neural systems for reading in children with dyslexia and indicate that it is evident at a young age. The locus of the disruption places childhood dyslexia within the same neurobiological framework as dyslexia, and acquired alexia, occurring in adults.

Adolescent↗

PubMed2002

Perception of speech and nonspeech stimuli by children with and without reading disability and attention deficit hyperactivity disorder.

The auditory temporal deficit hypothesis predicts that children with reading disability (RD) will exhibit deficits in the perception of speech and nonspeech acoustic stimuli in discrimination and temporal ordering tasks when the interstimulus interval (ISI) is short. Initial studies testing this hypothesis did not account for the potential presence of attention deficit hyperactivity disorder (ADHD). Temporal order judgment and discrimination tasks were administered to children with (1) RD/no-ADHD (n=38), (2) ADHD (n=29), (3) RD and ADHD (RD/ADHD; n=32), and (4) no impairment (NI; n=43). Contrary to predictions, children with RD showed no specific sensitivity to ISI and performed worse relative to children without RD on speech but not nonspeech tasks. Relationships between perceptual tasks and phonological processing measures were stronger and more consistent for speech than nonspeech stimuli. These results were independent of the presence of ADHD and suggest that children with RD have a deficit in phoneme perception that correlates with reading and phonological processing ability. (c) 2002 Elsevier Science (USA).

Adolescent↗

PubMed2002

Dissociation of sensitivity and response bias in children with attention deficit/hyperactivity disorder during central auditory masking.

Forty-three children (ages 7.0-14.5 years old) with and without attention deficit/hyperactivity disorder (ADHD), combined type had thresholds for detection of a 500-Hz pure tone estimated with and without a noise masker in the contralateral ear. The ear receiving the signal in the masked condition was varied randomly. A single-interval maximum-likelihood method estimated thresholds and false-alarm rate. Whereas the increase in threshold in children with ADHD in the presence of contralateral masking was comparable with controls, the increase in false-alarm rate was significantly greater. This dissociation between changes in sensitivity and response bias in the presence of masking noise supports suggestions that children with ADHD have difficulty inhibiting maladaptive responses and indicates that this deficit is quantifiable using psychoacoustic methods.

Adolescent↗

PubMed2002

Language development in children with spina bifida.

Spina bifida meningomyelocele (SBM) is the most common severely disabling birth defect in North America. It is a disorder of the central nervous system that includes, in addition to the defining spinal dysraphism, congenital malformations of the cerebellum and corpus callosum that, along with hydrocephalus, produces a range of cognitive and motor difficulties, including language. In the language domain, many children with SBM demonstrate adequate development of language at the level of form and content (grammar and lexicon). However, most children with SBM experience significant difficulties in the construction of meaning and in pragmatic communication, both of which require flexible language processing in real time. Assessment and intervention should specifically attend to the development of meaning construction and semantic-pragmatic communication.

Child↗

PubMed2002

Contributions of magnetic source imaging to the understanding of dyslexia.

The problem in dyslexia is difficulty learning how the printed word maps onto spoken language. Magnetic Source Imaging protocols were used in three studies. The first study with dyslexic children showed greater activity in the right temporoparietal region. The second study showed the aberrant neural circuit was present in initial stages of reading acquisition. The third study demonstrated that the aberrant profile could be normalized following intensive instruction. These findings suggest that dyslexia represents a functional deficit in the neural circuit that mediates the conversion of print to sound, which is amenable to change given adequate instruction.

Adolescent↗

PubMed2002

Brain mechanisms for reading words and pseudowords: an integrated approach.

The present study tested two predictions of dual-process models of reading: (i) that the brain structures involved in sublexical phonological analysis and those involved in whole-word phonological access during reading are different; and (ii) that reading of meaningful items, by means of the addressed phonology process, is mediated by different brain structures than reading of meaningless letter strings. We obtained brain activation profiles using Magnetic Source Imaging and, in addition, pronunciation latencies during reading of: (i) exception words (primarily involving addressed phonology and having meaning), (ii) pseudohomophones (requiring assembled phonology and having meaning), and (iii) pseudowords (requiring assembled phonology but having no meaning). Reading of meaningful items entailed a high degree of activation of the left posterior middle temporal gyrus (MTGp) and mesial temporal lobe areas, whereas reading the meaningless pseudowords was associated with much reduced activation of these two regions. Reading of all three types of print resulted in activation of the posterior superior temporal gyrus (STGp), inferior parietal and basal temporal areas. In addition, pronunciation speed of exception words correlated significantly with the onset of activity in MTGp but not STGp, whereas the opposite was true for pseudohomophones and pseudowords. These findings are consistent with the existence of two different brain mechanisms that support phonological processing in word reading: one mechanism that subserves assembled phonology and depends on the posterior part of STGp, and a second mechanism that is responsible for pronouncing words with rare print-to-sound correspondences and does not necessarily involve this region but instead appears to depend on MTGp.

Adult↗

PubMed2002

Brain activation profiles during the early stages of reading acquisition.

In the present study, we demonstrate for the first time the presence of an aberrant brain mechanism for reading in children who have just started acquiring reading skills. Children who, at the end of kindergarten, are found to be at risk for developing reading problems display markedly different activation profiles than children who have, at this stage, already mastered important prereading skills. This aberrant profile is characterized by the lack of engagement of the left-hemisphere superior temporal region, an area normally involved in converting print into sound, and an increase in activation in the corresponding right-hemisphere region. This finding is consistent with current cognitive models of reading acquisition and dyslexia, pointing to the critical role of phonologic awareness skills in learning to read.

Brain↗

PubMed2002

Object-based and action-based visual perception in children with spina bifida and hydrocephalus.

Children with spina bifida and hydrocephalus (SBH) have long been known to have difficulties with visual perception. We studied how children with SBH perform 12 visual perception tasks requiring object identification, multistable representations of visual space, or visually guided overt actions. Four tasks required object-based processing (visual constancy illusions, face recognition, recognition of fragmented objects, line orientation). Four tasks required the representation of visual space in egocentric coordinates (stereopsis, visual figure-ground identification, perception of multistable figures, egocentric mental rotation). Four tasks required the coupling of visual space to overt movement (visual pursuit, figure drawing, visually guided route finding, visually guided route planning). Effect sizes, measuring the magnitude of the difference between SBH children and controls, were consistently larger for action-based than object-based visual perception tasks. Within action-based tasks, effect sizes were large and roughly comparable for tasks requiring the representation of visual space and for tasks requiring visually guided action. The results are discussed in terms of the physical and brain problems of children with SBH that limit their ability to build effective situation models of space.

Adolescent↗

PubMedDate not supplied

Relationship of rapid automatized naming and phonological awareness in early reading development: implications for the double-deficit hypothesis.

It is widely accepted that deficits in phonological awareness skills are related to reading difficulties. Recently, another source of reading difficulty has been identified that involves naming speed, and combined impairments in phonological skills and naming speed will produce more severe reading deficits than single deficits in either of these cognitive skills. The purpose of this study was to investigate the consequences of grouping children based on the presence or absence of deficits in these skills. We demonstrate that the greater severity of reading impairment found in children with a double deficit could be due in part to a statistical artifact caused by grouping children based on their performance on two correlated continuous variables. This artifact also makes it difficult to establish the relative impact of deficits in naming speed on reading ability independent of deficits in phonological awareness.

Automation↗

PubMedDate not supplied

Psychometric approaches to the identification of LD: IQ and achievement scores are not sufficient.

Simulated data were used to demonstrate that groups formed by imposing cut-points based on either discrepancy or low-achievement definitions of learning disabilities (LD) are unstable over time. Similar problems were demonstrated in longitudinal data from the Connecticut Longitudinal Study, where 39% of the children designated as having LD in Grade 3 changed group placement with repeated testing in Grade 5. These results show that the practice of subdividing a normal distribution with arbitrary cut-points leads to instability in group membership. Approaches to the identification of children as having LD based solely on individual test scores not linked to specific behavioral criteria lead to invalid decisions about individual children. Low-achievement definitions are not a viable alternative to IQ-discrepancy definitions in the absence of other criteria, such as the traditional exclusions and response to quality intervention. If we accept the premise of multiple classes of low achievers, then we must develop identification systems that are valid and abandon systems whose only merits are their historical precedence and convenience.

Child↗

PubMedDate not supplied

Predicting math outcomes: reading predictors and comorbidity.

This commentary addresses issues concerning (a) the measurement of numbers, letters, and words versus cognitive processes in early screening batteries, and (b) comorbid associations of reading, math, and attention disorders. Based on reading prediction studies, assessments that include numbers should be most predictive of math outcomes. However, given the comorbid association of reading, math, and attention disorders, measures sensitive to reading and attention difficulties may be necessary in early screening batteries for math disabilities.

Attention Deficit Disorder with Hyperactivity↗