The genetic aspects of developmental dyslexia.

Discusses evidence concerning genetic influences on developmental dyslexia, a disorder characterized by difficulty in learning to read despite adequate opportunity and intelligence. Research on familial incidence, concordance in twins, the influence of parental age at the child's birth, and the subtyping of dyslexics is summarized. It is concluded that there is strong evidence for the heritability of a subtype based on verbal/language deficiency, perhaps reflecting reversed cerebral asymmetry, for which a genetic marker has been found. It is uncertain whether this subtype is caused by left hemispheric impairment or immaturity. There is somewhat weaker evidence for the heritability of a subtype based on visual/spatial deficiencies and a mixed subtype. (French abstract) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Development of bilateral motor control in children with developmental coordination disorders

This research examined behavioral (i.e. movement time) and neuromuscular (EMG) characteristics of unilateral and bilateral aiming movements of children with normal motor development and children with developmental coordination disorders (DCD). Two age groups of children were studied: 6 to 7, and 9 to 10 year olds. Bilateral aiming movements involved moving the two hands to targets of either (1) the same amplitude--symmetrical bilateral movements, or (2) different amplitudes--asymmetrical bilateral movements. Unilateral aiming movements involved moving one hand to either near or far targets associated with that hand. In general, unilateral and bilateral movement times were slower in younger than older children, and in children with DCD than children with normal motor development. Our neuromuscular data suggest that the faster movement times that typically accompany increasing age in children may be the result of a change in the capacity to initiate antagonist muscle contractions. The prolonged burst of agonist activity and delayed onset of antagonist activity observed in children with DCD may contribute to their inability to produce fast, accurate unilateral movements. On both symmetrical and asymmetrical bilateral aiming movements, children with DCD had more performance errors and greater temporal inconsistencies between neuromuscular (EMG) parameters and behavioral (movement time) parameters than children with normal motor development. These new neuromuscular data suggest that there are important differences in the way the motor control systems of children with and without DCD organize bilateral aiming responses.     

Double dissociation of functions in developmental dyslexia and dyscalculia.

This work examines the association between symbols and their representation in adult developmental dyscalculia and dyslexia. Experiment 1 used comparative judgment of numerals, and it was found that in physical comparisons (e.g., 3-5 vs. 3-5) the dyscalculia group showed a significantly smaller congruity effect than did the dyslexia and the control groups. Experiment 2 used Navon figures (D. Navon, 1977) in Hebrew, and participants were asked to name the large or the small letters. Phoneme similarity modulated performance of the control and the dyscalculia groups and showed a very small effect in the dyslexia group. This suggests that the dyscalculia population has difficulties in automatically associating numerals with magnitudes but no problems in associating letters with phonemes, whereas the dyslexia population shows the opposite pattern. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A test of motor (not executive) planning in developmental coordination disorder and autism.

Grip selection tasks have been used to test “planning” in both autism and developmental coordination disorder (DCD). We differentiate between motor and executive planning and present a modified motor planning task. Participants grasped a cylinder in 1 of 2 orientations before turning it clockwise or anticlockwise. The rotation resulted in a comfortable final posture at the cost of a harder initial reaching action on 50% of trials. We hypothesized that grip selection would be dominated by motoric developmental status. Adults were always biased towards a comfortable end-state with their dominant hand, but occasionally ended uncomfortably with their nondominant hand. Most 9- to 14-year-olds with and without autism also showed this “end-state comfort” bias but only 50% of 5- to 8-year-olds. In contrast, children with DCD were biased towards selecting the simplest initial movement. Our results are best understood in terms of motor planning, with selection of an easier initial grip resulting from poor reach-to-grasp control rather than an executive planning deficit. The absence of differences between autism and controls may reflect the low demand this particular task places on executive planning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

M-stream deficits and reading-related visual processes in developmental dyslexia.

Some visual processing deficits in developmental dyslexia have been attributed to abnormalities in the subcortical M stream and/or the cortical dorsal stream of the visual pathways. The nature of the relationship between these visual deficits and reading is unknown. The purpose of the present article was to characterize reading-related perceptual processes that may link the visual deficits to reading problems. We identified contrast sensitivity, position encoding, oculomotor control, visual attention, parafoveal/foveal interactions, and saccadic suppression as potential reading-related dorsal stream processes. We then evaluated the role of each process in reading and the status of each process in dyslexia. In theory, a number of dorsal stream processes (e.g., oculomotor control and visual attention) might contribute to reading problems in developmental dyslexia. More work is needed to demonstrate the connection empirically. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The cognitive profile and multiple-deficit hypothesis in Chinese developmental dyslexia.

The present study was conducted to examine the cognitive profile and multiple-deficit hypothesis in Chinese developmental dyslexia. Thirty Chinese dyslexic children in Hong Kong were compared with 30 average readers of the same chronological age (CA controls) and 30 average readers of the same reading level (RL controls) in a number of rapid naming, visual, phonological, and orthographic tasks. Chinese dyslexic children performed significantly worse than the CA controls but similarly to the RL controls on most of the cognitive tasks. The rapid naming deficit was found to be the most dominant type of cognitive deficit in Chinese dyslexic children. Over half of the dyslexic children exhibited deficits in 3 or more cognitive areas, and there was a significant association between the number of cognitive deficits and the degree of reading and spelling impairment. The present findings support the multiple-deficit hypothesis in Chinese developmental dyslexia. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects and timing of developmental peer appraisals in self-managing work groups.

This study used a repeated measures time-series design to examine the immediate and longer term impact of a structured, face-to-face developmental peer appraisal on 294 undergraduates in 44 self-managing work groups (SMWGs) and 217 MBA students in 36 SMWGs. Results revealed an immediate positive impact on perceptions of open communication, task motivation, social loafing, group viability, cohesion, and satisfaction. Also, the effects of the peer appraisal were not dependent on the perceived ratio of positive to negative feedback, and the enduring impact of the appraisal was influenced by its timing relative to task deadline. Overall, results emphasized that peer appraisals can have a positive effect on relationships and task focus, are influenced by temporal context, and have great potential for work teams. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Word recognition in developmental dyslexia: a connectionist interpretation

We present a study of the accuracy, consistency, and speed of word naming in a dyslexic boy, JM, who has severe impairments in the ability to use sub-lexical, phonological reading strategies. For words that he can recognise, JM's naming latencies do not differ from those of control subjects matched for reading age, and he is generally consistent from one occasion to the next. He can also match printed homophones with their definitions--a skill that requires access to well-specified orthographic representations. The data are interpreted as evidence for the creation of efficient recognition devices for words within JM's sight vocabulary. However, he shows a continuing inability to use phonological decoding strategies to deal with words that he cannot recognize by sight. Overall we argue our results pose problems for stage models of reading development, and that they may best be interpreted within a connectionist framework of the development of word recognition skills.     

On subtypes of developmental dyslexia: Evidence from processing time and accuracy scores.

Determined the proportion of phonological dyslexics (Ph-DYS) and surface dyslexics (S-DYS) in a population of French dyslexics by applying A. Castles and M. Coltheart's (1993) regression method to 2 diagnostic measures: pseudo-word and irregular-word processing time. 31 dyslexics were matched to 19 average readers of the same age (aged 10 yrs, CA controls) and to 19 younger children of the same reading level (aged 8 yrs, RL controls). Compared to CA controls, there were more Ph-DYS than S-DYS. Compared to RL controls, there were still a high number of Ph-DYS. The reliability of these subtypes across different measures of phonological and orthographic skills was also examined. Compared to RL controls, both groups of dyslexics were found to be impaired only in phonological skills. The moment at which the 2 dissociated profiles emerged in the course of cognitive development was assessed by examining data that was collected when the children were 7 and 8 yrs old. The results show that only the S-DYS's orthographic deficit increased with development. The authors also looked at whether the Ph-DYS and S-DYS profiles were associated with other specific cognitive deficits. Specific deficits in phonemic awareness and in phonological short-term memory were found for both Ph-DYS and S-DYS. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Bimanual motor coordination in agenesis of the corpus callosum.

The nature and extent of deficiencies in bimanual motor coordination in individuals with agenesis of the corpus callosum (ACC) was studied using the computerized Bimanual Coordination Test (cBCT). Compared with previous bimanual tasks, the cBCT is more specifically reliant on interhemispheric interactions of lateralized motor control, allows more precise measurement, and permits examination of performance over a wider range of bimanual challenges. The cBCT performance of 13 high-functioning individuals with complete ACC was compared to 21 age- and IQ-matched controls. The groups did not differ in unimanual response speed. On trials involving angled paths that require bimanual coordination, the ACC group performed significantly slower and less accurately across all angles. The largest group differences in speed occurred on trials where the hands must respond symmetrically, while mirror-image (vs. parallel) responding produced the greatest deficits in accuracy. These data confirm previous findings of deficits in bimanual coordination in callosal absence, but using significantly improved measurement technology. Deficits in bimanual coordination in ACC are present across different demands for interhand interactions in the speed and direction of movement. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Neural systems affected in developmental dyslexia revealed by functional neuroimaging

Spiral ganglion neurones in rat cochlea express three different isoforms of the P2X2 receptor subunit which assemble into ATP-gated ion channels. Two of these P2X2R subunit isoforms have previously been detected in other auditory tissues. The third isoform (designated P2X2-3R) has not been described. This isoform lacks 39 bp immediately prior to the stop codon, corresponding to a 13 amino acid deletion of the extreme C-terminus domain. Using direct in situ RT-PCR, expression of P2X2R mRNA was confined to a subpopulation of type I spiral ganglion neurones. This study supports a role for extracellular ATP as a neurotransmitter for a discrete population of auditory neurones where variation in P2X2R isoform assembly may confer functional heterogeneity, including enhanced desensitization.     

Understanding chinese developmental dyslexia: Morphological awareness as a core cognitive construct.

Tasks representing 9 cognitive constructs of potential importance to understanding Chinese reading development and impairment were administered to 75 children with dyslexia and 77 age-matched children without reading difficulties in 5th and 6th grade. Logistic regression analyses revealed that dyslexic readers were best distinguished from age-matched controls with tasks of morphological awareness, speeded number naming, and vocabulary skill; performance on tasks of visual skills or phonological awareness failed to distinguish the groups. Path analyses further revealed that a construct of morphological awareness was the strongest consistent predictor of a variety of literacy-related skills across both groups. Findings suggest that morphological awareness may be a core theoretical construct necessary for explaining variability in reading Chinese. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Perceptual learning immediately yields new stable motor coordination.

Coordinated rhythmic movement is specifically structured in humans. Movement at 0° mean relative phase is maximally stable, 180° is less stable, and other coordinations can, but must, be learned. Variations in perceptual ability play a key role in determining the observed stabilities so we investigated whether stable movements can be acquired by improving perceptual ability. We assessed movement stability in Baseline, Post Training, and Retention sessions by having participants use a joystick to coordinate the movement of two dots on a screen at three relative phases. Perceptual ability was also assessed using a two-alternative forced choice task in which participants identified a target phase of 90° in a pair of displays. Participants then trained with progressively harder perceptual discriminations around 90° with feedback. Improved perceptual discrimination of 90° led to improved performance in the movement task at 90° with no training in the movement task. The improvement persisted until Retention without further exposure to either task. A control group's movement stability did not improve. Movement stability is a function of perceptual ability, and information is an integral part of the organization of this dynamical system. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The developmental origins of bimanual coordination: A dynamic perspective.

Patterns of interlimb coordination associated with infant reaching fluctuate frequently over developmental time. This study investigated whether these fluctuations are related to coordination tendencies. Interlimb patterns were studied in reaching and nonreaching movements in 4 infants, which were followed through their 1st year. Each week, reaching and nonreaching endpoint kinematics were recorded in both arms during multiple 14-s trials. It was found that patterns of interlimb coordination in reaching matched coordination tendencies in nonreaching. Reaching fluctuated between uni- and bimanual periods. During the bimanual periods, nonreaching interlimb activity tended to be synchronous. During the unimanual periods, nonreaching activity revealed no predominant form of interlimb coordination. It is argued that changing coordination tendencies may influence the organization of specific goal-oriented behaviors from early in life. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Transfer of learning among motor patterns with different relative timing.

The generalized motor program concept with invariant relative timing leads one to expect nearly perfect transfer of training to a motor pattern with another duration and considerably less transfer to a pattern with a different relative timing. In two experiments, subjects were asked to learn spatial–temporal patterns of limb action at the elbow. These expectations about differential transfer were examined by the use of two target patterns that differed only by a nonlinear transformation of the time scale. Both experiments failed to provide evidence that transfer breaks down if relative timing is changed. These outcomes are taken to suggest that the often observed invariant relative timing might not be a mandatory phenomenon due to the restriction of a generalized motor program to one particular temporal pattern. Rather, this invariance could perhaps be thought of as a strategic phenomenon caused by preferences for certain temporal organizations contingent upon particular spatial patterns. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Proprioception versus motor outflow in timing: A reply to Jones.

Discusses B. Jones's (see record 1973-20006-001) argument that the motor outflow hypothesis should be considered a rival to the proprioceptive feedback interpretation of the motor response timing data reviewed by Schmidt. However, with no data ruling in favor of motor outflow over proprioceptive feedback for timing, and with other peripheral feedback channels (e.g., vision) known to be mechanisms for timing, the proprioceptive feedback explanation is favored over motor outflow. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Metabolic abnormalities in developmental dyslexia detected by 1H magnetic resonance spectroscopy

BACKGROUND: Neurological and physiological deficits have been reported in the brain in developmental dyslexia. The temporoparietal cortex has been directly implicated in dyslexic dysfunction, and substantial indirect evidence suggests that the cerebellum is also implicated. We wanted to find out whether the neurological and physiological deficits manifested as biochemical changes in the brain. METHODS: We obtained localised proton magnetic resonance spectra bilaterally from the temporo-parietal cortex and cerebellum of 14 well-defined dyslexic men and 15 control men of similar age. FINDINGS: We found biochemical differences between dyslexic men and controls in the left temporo-parietal lobe (ratio of choline-containing compounds [Cho] to N-acetylaspartate [NA] p< or =0.01) and right cerebellum (Cho/NA, p< or = 0.01; creatine [Cre] to NA p< or =0.05; (not significant). We found lateral biochemical differences in dyslexic men in both these brain regions (Cho/NA in temporo-parietal lobe, left vs right, p< or =0.01; Cre/NA in cerebellum, left vs right, p< or =0.001). We found no such lateral differences in controls. There was no significant relation between the degree of contralateral chemical difference and handedness in dyslexic or control men. INTERPRETATION: We suggest that the observed differences reflect changes in cell density in the temporo-parietal lobe in developmental dyslexia and that the altered cerebral structural symmetry in dyslexia is associated with abnormal development of cells or intracellular connections or both. The cerebellum is biochemically asymmetric in dyslexic men, indicating altered development of this organ. These differences provide direct evidence of the involvement of the cerebellum in dyslexic dysfunction.     

Impaired motor coordination in mice lacking prion protein

1. Prion protein (PrPC) is a host-encoded glycoprotein constitutively expressed on the neuronal cell surface. Accumulation of its protease-resistant isoform is closely related to pathologic changes and prion propagation in the brain tissue of a series of prion diseases. However, the physiological role of PrPC remains to be elucidated. 2. After long-term observation, we noted impaired motor coordination and loss of cerebellar Purkinje cells in the aged mice homozygous for a disrupted PrP gene, a finding which strongly suggests that PrPC plays a role in the long-term survival of Purkinje cells. 3. We also describe the resistance of the PrP null mice to the prion, indicating the requirement of PrPC for both the development of prion diseases and the prion propagation.     

Primary motor cortex is involved in bimanual coordination

Many voluntary movements involve coordination between the limbs. However, there have been very few attempts to study the neuronal mechanisms that mediate this coordination. Here we have studied the activity of cortical neurons while monkeys performed tasks that required coordination between the two arms. We found that most neurons in the primary motor cortex (MI) show activity specific to bimanual movements (bimanual-related activity), which is strikingly different from the activity of the same neurons during unimanual movements. Moreover, units in the supplementary motor area (SMA; the area of cortex most often associated with bimanual coordination) showed no more bimanual-related activity than units in MI. Our results challenge the classic view that MI controls the contralateral (opposite) side of the body and that SMA is responsible for the coordination of the arms. Rather, our data suggest that both cortical areas share the control of bilateral coordination.     

The timing of color and location processing in the motor context

The contribution of migratory and resident birds to the introduction of Lyme disease will vary with the degree to which various species expose themselves to, and are infested by, juvenile vector ticks, and their ability to support and transmit the infectious agent. To examine the relative contribution of various passerine species during the emergence of this disease, we compared the abundance and infection rates of the blacklegged tick, Ixodes scapularis Say, removed from mist-netted birds with those from live-trapped mice at a coastal study site in southern Maine, collected during an 8-yr period in which the range of this tick and the incidence of Lyme disease increased in the state. Weekly bird-banding sessions using six 12-m Japanese mist nets were carried out from May through August 1989-1996. In 1989, 1991 and 1993, mice were live-trapped in a Sherman trap grid (7 by 7 m) during five 3-night sessions, June through August; in 1994-1996, 2 such grids were similarly trapped. Annual adult tick abundance was estimated by flagging vegetation. We removed 2,633 juvenile deer ticks from 1,713 of 1,972 birds examined. Twenty-five of 64 bird species were infested. The percentages of birds infested and the rate of infection among removed larvae and nymphs increased over the years, but species varied markedly in their ability to infect ticks. No infected larvae were removed from catbirds or towhees. The larval to nymphal ratio was higher in mice than in birds. Infection rates among bird-derived larvae were less than among mice-derived larvae, but increased with time. Because of the different ways in which individual species of passerine birds contribute to the availability of vector ticks and respond to the agent of Lyme disease in emerging areas, further research into host competency and borreliacidal mechanisms is needed.