Symptoms of hyperactivity and inattention can mediate deficits of postural stability in developmental dyslexia

Motor skills and capacities in developmental dyslexia: A systematic review and meta-analysis

In recent decades, the connections between academic skills, such as reading, writing, and calculation, and motor skills/capacities have received increasing attention. Many studies provided evidence for motor difficulties in children and adolescents with dyslexia, prompting the need for a meta-analysis to combine these multiple findings. Therefore, we conducted a meta-analysis using PsycINFO, Pubmed, and SportDiscus as scientific databases. A total of 572 studies were analyzed following several stringent inclusion criteria, resulting in the inclusion of 23 peer-reviewed studies in the final analysis. Our results showed that children and adolescents with dyslexia displayed significant different performances in multiple motor tasks and these differences persisted also when the type of motor task was considered as moderator in the analysis. The present findings are in accordance with the literature that supports a close connection between reading disabilities and difficulties in motor skills/capacities.

Dysgraphia Differs Between Children With Developmental Coordination Disorder and/or Reading Disorder

Handwriting deficits, or dysgraphia, are present in several neurodevelopmental disorders. To investigate whether dysgraphia differs according to the associated disorder, we performed a detailed analysis of handwriting in children with developmental coordination disorders (DCD), reading disorder (RD), or comorbid RD and DCD. Handwriting deficits were investigated at the product (quality of the trace) and the process (movement that generates the trace) levels. Nineteen children with singular RD (among which eight with dysgraphia), 13 children with singular DCD (among which seven with dysgraphia), 16 children with comorbid RD+DCD (among which 11 with dysgraphia), and 20 typically developing children, age 7 to 12, performed the BHK (Brave Handwriting Kinder) test, a standardized assessment of handwriting, on a graphic tablet. Developmental coordination disorders primarily affected handwriting quality, while RD affected slowness and, to a lesser extent, quality. Children with RD, solely or comorbid with DCD, wasted time by lifting and stopping the pen when writing. The comorbidity added to but did not worsen, handwriting difficulties. These results reflect distinct motor impairments and/or strategies in children with DCD or RD. We identified subtypes of dysgraphia and advocated for a fine-grained analysis of the writing process and the assessment of motor and reading skills when studying dysgraphia.

Is part-time special education beneficial for children at risk for reading difficulties? An example from Estonia

This longitudinal quasi-experimental study examined the general efficiency of part-time special education for students at risk for reading difficulties in Estonian primary schools. Participants were selected from 464 students whose pre-reading and reading skills were assessed for the study at the beginning of school. Eighty-four of these children received part-time special education support throughout the first grade (treatment group). Statistical matching was used to find a control group similar to the treatment group on pre-reading skills and parental educational level but who did not receive extra help (control group; 84 children). Students' reading fluency and task persistence were assessed at the end of Grade 1 and Grade 2. Neither group differed in reading fluency nor task persistence at the end of either grade. Developmental trajectories of those treatment group children who received additional support only for reading and spelling difficulties did not differ from those who received this support for concurrent developmental disorders in addition to reading and spelling difficulties. Our findings indicate that a full-year of special education support in the form of extra lessons without a prior diagnostic assessment, frequent progress monitoring, or focused interventions might not be an effective way to support children with reading difficulties.

Quantitative assessment of drawing tests in children with dyslexia and dysgraphia

Drawing tests in children diagnosed with dyslexia and dysgraphia were quantitatively compared. Fourteen children with dysgraphia, 19 with dyslexia and 13 normally developing were asked to copy 3 figures: a circle, a square and a cross. An optoelectronic system allowed the acquisition of the drawing track in three-dimensions. The participants' head position and upper limb movements were measured as well. A set of parameters including movement duration, velocity, length of the trace, Range of Motion of the upper limb, was computed and compared among the 3 groups. Children with dyslexia traced the circle faster than the other groups. In the cross test, dyslexic participants showed a reduced execution time and increased velocity while drawing the horizontal line. Children with dyslexia were also faster in drawing certain sides of square with respect to the other groups.

Examining links between cognitive markers, movement initiation and change, and pedestrian safety in older adults

OBJECTIVE

The purpose of this study was to determine the extent to which mobility indices (such as walking speed and postural sway), motor initiation, and cognitive function, specifically executive functions, including spatial planning, visual attention, and within participant variability, differentially predicted collisions in the near and far sides of the road with increasing age.

METHODS

Adults aged over 45 years participated in cognitive tests measuring executive function and visual attention (using Useful Field of View; UFoV(®)), mobility assessments (walking speed, sit-to-stand, self-reported mobility, and postural sway assessed using motion capture cameras), and gave road crossing choices in a two-way filmed real traffic pedestrian simulation.

RESULTS

A stepwise regression model of walking speed, start-up delay variability, and processing speed) explained 49.4% of the variance in near-side crossing errors. Walking speed, start-up delay measures (average and variability), and spatial planning explained 54.8% of the variance in far-side unsafe crossing errors. Start-up delay was predicted by walking speed only (explained 30.5%).

CONCLUSION

Walking speed and start-up delay measures were consistent predictors of unsafe crossing behaviours. Cognitive measures, however, differentially predicted near-side errors (processing speed), and far-side errors (spatial planning). These findings offer potential contributions for identifying and rehabilitating at-risk older pedestrians.

The distinctive vertical heterophoria of dyslexics

In this study, we looked for the presence of vertical heterophoria (VH) in 42 dyslexic children (22 males and 20 females) aged 118.5±12.9 months who were compared with a control group of 22 nondyslexic children (eleven males and eleven females) aged 112±9.8 months. Dyslexics presented a low-level (always <1 prism diopter) VH combined with torsion. This oculomotor feature clearly separates the dyslexic group from the normal readers group. It is independent of the type of dyslexia. The essential feature of this VH is a lability that appears during specific stimulation of sensory receptors involved in postural regulation. This lability is demonstrated using a vertical Maddox test conducted under very specific conditions in which postural sensors are successively stimulated in a predetermined order. A quantitative variation in this VH may be seen during the Bielchowsky Head Tilt Test, which reveals hypertonia of the lower or upper oblique muscles. Vertical orthophoria can be achieved by placing low-power prisms asymmetrically within the direction of action of the superior or inferior oblique muscles. The selection of power and axis is not only guided by elements of the eye examination but also from observation of postural muscle tone. All these elements suggest that the VH could be of postural origin and somehow related to the vertical action of the oblique muscles. VH and torsion are not harmful per se. There is no statistical relationship between their level and the various parameters used to assess the reading skills of dyslexic children. VH and torsion could be a clinical marker of global proprioceptive dysfunction responsible for high-level multisensory disturbances secondary to poor spatial localization of visual and auditory information. This dysfunction might also explain the motor disorders concomitant to dyslexia.

Adults with dyslexia demonstrate large effects of crowding and detrimental effects of distractors in a visual tilt discrimination task

Previous research has shown that adults with dyslexia (AwD) are disproportionately impacted by close spacing of stimuli and increased numbers of distractors in a visual search task compared to controls [1]. Using an orientation discrimination task, the present study extended these findings to show that even in conditions where target search was not required: (i) AwD had detrimental effects of both crowding and increased numbers of distractors; (ii) AwD had more pronounced difficulty with distractor exclusion in the left visual field and (iii) measures of crowding and distractor exclusion correlated significantly with literacy measures. Furthermore, such difficulties were not accounted for by the presence of covarying symptoms of ADHD in the participant groups. These findings provide further evidence to suggest that the ability to exclude distracting stimuli likely contributes to the reported visual attention difficulties in AwD and to the aetiology of literacy difficulties. The pattern of results is consistent with weaker and asymmetric attention in AwD.

Magnocellular-dorsal pathway and sub-lexical route in developmental dyslexia

Although developmental dyslexia (DD) is frequently associate with a phonological deficit, the underlying neurobiological cause remains undetermined. Recently, a new model, called "temporal sampling framework" (TSF), provided an innovative prospect in the DD study. TSF suggests that deficits in syllabic perception at a specific temporal frequencies are the critical basis for the poor reading performance in DD. This approach was presented as a possible neurobiological substrate of the phonological deficit of DD but the TSF can also easily be applied to the visual modality deficits. The deficit in the magnocellular-dorsal (M-D) pathway - often found in individuals with DD - fits well with a temporal oscillatory deficit specifically related to this visual pathway. This study investigated the visual M-D and parvocellular-ventral (P-V) pathways in dyslexic and in chronological age and IQ-matched normally reading children by measuring temporal (frequency doubling illusion) and static stimuli sensitivity, respectively. A specific deficit in M-D temporal oscillation was found. Importantly, the M-D deficit was selectively shown in poor phonological decoders. M-D deficit appears to be frequent because 75% of poor pseudo-word readers were at least 1 SD below the mean of the controls. Finally, a replication study by using a new group of poor phonological decoders and reading level controls suggested a crucial role of M-D deficit in DD. These results showed that a M-D deficit might impair the sub-lexical mechanisms that are critical for reading development. The possible link between these findings and TSF is discussed.

Postural control is not systematically related to reading skills: implications for the assessment of balance as a risk factor for developmental dyslexia

Impaired postural control has been associated with poor reading skills, as well as with lower performance on measures of attention and motor control variables that frequently co-occur with reading difficulties. Measures of balance and motor control have been incorporated into several screening batteries for developmental dyslexia, but it is unclear whether the relationship between such skills and reading manifests as a behavioural continuum across the range of abilities or is restricted to groups of individuals with specific disorder phenotypes. Here were obtained measures of postural control alongside measures of reading, attention and general cognitive skills in a large sample of young adults (n = 100). Postural control was assessed using centre of pressure (CoP) measurements, obtained over 5 different task conditions. Our results indicate an absence of strong statistical relationships between balance measures with either reading, cognitive or attention measures across the sample as a whole.

Comorbidities in preschool children at family risk of dyslexia

BACKGROUND

Comorbidity among developmental disorders such as dyslexia, language impairment, attention deficit/hyperactivity disorder and developmental coordination disorder is common. This study explores comorbid weaknesses in preschool children at family risk of dyslexia with and without language impairment and considers the role that comorbidity plays in determining children's outcomes.

METHOD

The preschool attention, executive function and motor skills of 112 children at family risk for dyslexia, 29 of whom also met criteria for language impairment, were assessed at ages 3½ and 4½ years. The performance of these children was compared to the performance of children with language impairment and typically developing controls.

RESULTS

Weaknesses in attention, executive function and motor skills were associated with language impairment rather than family risk status. Individual differences in language and executive function are strongly related during the preschool period, and preschool motor skills predicted unique variance (4%) in early reading skills over and above children's language ability.

CONCLUSION

Comorbidity between developmental disorders can be observed in the preschool years: children with language impairment have significant and persistent weaknesses in motor skills and executive function compared to those without language impairment. Children's early language and motor skills are predictors of children's later reading skills.

Cerebellar function in developmental dyslexia

Developmental dyslexia is a genetically based neurobiological syndrome, which is characterized by reading difficulty despite normal or high general intelligence. Even remediated dyslexic readers rarely achieve fast, fluent reading. Some dyslexics also have impairments in attention, short-term memory, sequencing (letters, word sounds, and motor acts), eye movements, poor balance, and general clumsiness. The presence of "cerebellar" motor and fluency symptoms led to the proposal that cerebellar dysfunction contributes to the etiology of dyslexia. Supporting this, functional imaging studies suggest that the cerebellum is part of the neural network supporting reading in typically developing readers, and reading difficulties have been reported in patients with cerebellar damage. Differences in both cerebellar asymmetry and gray matter volume are some of the most consistent structural brain findings in dyslexics compared with good readers. Furthermore, cerebellar functional activation patterns during reading and motor learning can differ in dyslexic readers. Behaviorally, some children and adults with dyslexia show poorer performance on cerebellar motor tasks, including eye movement control, postural stability, and implicit motor learning. However, many dyslexics do not have cerebellar signs, many cerebellar patients do not have reading problems, and differences in dyslexic brains are found throughout the whole reading network, and not isolated to the cerebellum. Therefore, impaired cerebellar function is probably not the primary cause of dyslexia, but rather a more fundamental neurodevelopmental abnormality leads to differences throughout the reading network.

Occlusal traits in developmental dyslexia: a preliminary study

AIM

The objective of the study reported here was to assess the orthodontic features in children affected by developmental dyslexia (DD).

PATIENTS AND METHODS

A total of 28 children affected by DD (22 boys, six girls; mean age: 9.78 ± 1.69 years) were compared with 51 healthy children (38 boys, 13 girls; mean age 9.41 ± 1.48; range 7-10 years). Reading and writing skills were evaluated along with orthodontic features.

RESULTS

The DD and control groups were not significantly different in terms of total intelligence quotient (P = 0.441) and writing skills (P = 0.805 and P = 0.240, respectively), whereas significant differences were observed between the DD group and control group in both word reading (2.018 ± 1.714 vs 0.917 ± 0.563; P = 0.000) and non-word reading (2.537 ± 1.543 vs 0.862 ± 0.244; P = 0.000). Moreover, for many orthodontic features, there was no significant difference between the two groups; only in prevalence of diastemas (57.14%, P = 0.006), midline diastemas (46.42%, P = 0.007), overbite > 4 mm (71.42%, P = 0.006) and overjet > 4 mm (53.57%, P = 0.001), was there a statistically significant difference. According to univariate logistic regression analysis, the presence of diastemas (odds ratio [OR] 4.33; 95% confidence interval [CI] 1.61-11.65), midline diastemas (OR 4.68; 95% CI 1.61-13.43), an overbite >4 mm (OR 1.75; 95% CI 0.64-4.71), or an overjet >4 mm (OR 2.76; 95% CI 1.06-7.20) seems to play a role in the relationship between occlusal abnormalities and DD in children.

CONCLUSION

Children with DD tend to present with altered dental features, particularly in the area of the incisors, suggesting that a persistently different tongue kinematic profile may thus affect both the developmental variability of the tongue and lip and the occlusion.

Spherical lenses and prisms lead to postural instability in both dyslexic and non dyslexic adolescents

There is controversy as to whether dyslexic children present systematic postural deficiency. Clinicians use a combination of ophthalmic prisms and proprioceptive soles to improve postural performances. This study examines the effects of convergent prisms and spherical lenses on posture. Fourteen dyslexics (13-17 years-old) and 11 non dyslexics (13-16 years-old) participated in the study. Quiet stance posturography was performed with the TechnoConcept device while subjects fixated a target at eye-level from a distance of 1_m. Four conditions were run: normal viewing; viewing the target with spherical lenses of -1 diopter (ACCOM1) over each eye; viewing with -3 diopters over each eye (ACCOM3); viewing with a convergent prism of 8 diopters per eye. Relative to normal viewing, the -1 lenses increased the surface of body sway significantly whereas the -3 diopter lenses only resulted in a significant increase of antero-posterior body sway. Thus, adolescents would appear to cope more effectively with stronger conflicts rather than subtle ones. The prism condition resulted in a significant increase in both the surface and the antero-posterior body sway. Importantly, all of these effects were similar for the two groups. Wavelet analysis (time frequency domain) revealed high spectral power of antero-posterior sway for the prism condition in both groups. In the ACCOM3 condition, the spectral power of antero-posterior sway decreased for non dyslexics but increased for dyslexics suggesting that dyslexics encounter more difficulty with accommodation. The cancelling time for medium range frequency (believed to be controlled by the cerebellum), was shorter in dyslexics, suggesting fewer instances of optimal control. We conclude that dyslexics achieve similar postural performances albeit less efficiently. Prisms and lenses destabilize posture for all teenagers. Thus, contrary to adults, adolescents do not seem to use efferent, proprioceptive ocular motor signals to improve their posture, at least not immediately when confronted to convergence accommodation conflict.

Project DyAdd: classical eyeblink conditioning in adults with dyslexia and ADHD

In this study of the project DyAdd (Adult Dyslexia and Attention Deficit Disorder in Finland), classical eyeblink conditioning (EBC) was investigated in both delay and trace paradigms in adults (18-55 years) with dyslexia (n = 37), attention deficit-hyperactivity disorder (ADHD; n = 21), their comorbid combination (n = 8), and healthy controls (n = 35). In addition, the profiles of three participants with a rare autosomal dominant cerebellar disease were assessed (episodic ataxia type 2, EA-2). We found that participants with dyslexia were overall slower learners than controls in eyeblink conditioning. Further, they were the only group that had a reduced number of CRs in mediotemporal-dependent trace paradigm compared to the more cerebellum-dependent delay paradigm. Second, ADHD was found to be related to larger CR amplitude. Third, those with a comorbid condition learned faster and manifested CRs that were not well timed. Fourth, the cerebellar patients showed nearly no conditioning at all. Correlations between EBC and various neuropsychological domains (phonological processing, reading, spelling, arithmetic, executive functions, attention, and fine motor control) over all participants resulted in significant relations only for the delay paradigm: Increased amount of reading errors related with later peak latency and increased amount of self-corrections in fine motor control related with larger response magnitude. Within those who conditioned, relations emerged only for the trace paradigm: better spelling was related to larger response magnitude. These results do not lend support to the cerebellar hypothesis of dyslexia. On the contrary, dyslexia in its pure form seems to be related to a relative dysfunction of a larger hippocampal-cerebellar network. Further, larger responses in the ADHD group are suggested to result from their lowered responding threshold.

Predictors of postural stability in children with ADHD

OBJECTIVE

As children with ADHD who have more inattention problems are more frequently with fine motor problems, it is not clear whether postural balance problems are associated with different subtypes of ADHD. This study investigates the predictors of postural stability in children with ADHD considering the covariant factors of age, gender, and comorbidities.

METHOD

A total of 103 children with ADHD are studied using Poor Postural Stability Questionnaire filled out by their parents.

RESULTS

Linear regression analysis indicates that only oppositional-defiant behavior score is the predictor of seeking-movement subscale score. ADHD type does not predict the score of avoiding-postural-instability subscale, whereas separation anxiety score did so.

CONCLUSION

ADHD subtypes do not have distinct clinical profiles of the balance problems. Postural stability in children with ADHD depends on the comorbid psychiatric disorders rather than ADHD subtypes.

Sensory processing problems in children with ADHD, a systematic review

One of the most common psychiatric disorders in children is attention deficit hyperactivity disorder (ADHD). Its course and outcome are heterogeneous. Sensory processing problems impact the nature of response to daily events. ADHD and sensory problems may occur together and interact. No published review article about sensory processing problems in children with ADHD were found. A systematic search, conducted on Pub-Med (up to January 2010), and Google Scholar, yielded 255 abstracts on sensory processing problems in children including 11 studies about sensory problems in children with ADHD. Sensory processing problems in children with ADHD is not a well studied area. Sensory processing problems in children with ADHD are more common than in typically developing children. Findings do not support that ADHD subtypes are distinct disorders with regard to sensory processing problems. However, co-morbidity with oppositional defiant disorder and anxiety are predictors of more severe sensory processing problems in children with ADHD.

Postural control during the Stroop test in dyslexic and non dyslexic teenagers

Postural control in quiet stance although simple still requires some cognitive resources; dual cognitive tasks influence further postural control. The present study examines whether or not dyslexic teenagers experience postural instability when performing a Stroop dual task for which their performances are known to be poor. Fifteen dyslexics and twelve non-dyslexics (14 to 17 years old) were recruited from the same school. They were asked to perform three tasks: (1) fixate a target, (2) perform an interference Stroop test (naming the colour or the word rather than reading the word), (3) performing flexibility Stroop task: the subject performed the interference task as in (2) except when the word was in a box, in which case he had to read the word. Postural performances were measured with a force platform. The results showed a main task effect on the variance of speed of body sway only: such variance was higher in the flexibility task than for the other two tasks. No group effect was found for any of the parameters of posture (surface, mediolateral and anteroposterior sway, variance of speed). Further wavelet analysis in the time-frequency domain revealed an increase in the spectral power of the medium frequency range believed to be related to cerebellum control; an accompanying increase in the cancellation time of the high frequency band related to reflexive loops occurred for non-dyslexics only. These effects occurred for the flexibility task and could be due to its high cognitive difficulty. Dyslexics displayed shorter cancellation time for the medium frequency band for all tasks, suggesting less efficient cerebellar control, perhaps of eye fixation and attention influencing body sway. We conclude that there is no evidence for a primary posture deficit in 15 year old teenagers who come from the general population and who were recruited in schools.

Are balance problems connected to reading speed or the familial risk of dyslexia?

AIM

The aim of this study was to examine the connection between balance problems and reading speed in children with and without a familial risk of dyslexia by controlling for the effects of attention, hyperactivity, and cognitive and motor functioning.

METHOD

The prevalence of balance problems was studied in 94 children (48 females, 46 males) with a familial risk of dyslexia (at-risk group) and 85 children (38 females, 47 males) without a risk of dyslexia (comparison group). Further, the relationships between balance problems (at age 8y 6mo), reading proficiency (at age 9y), attention-deficit-hyperactivity disorder (at age 8y), and cognitive (at age 8y 6mo) and motor functioning (at age 6y 6mo) were examined. Inclusion criteria for the at-risk group were that at least one parent had a confirmed reading problem and one or more of the parents' close relatives also had a reading problem. The Good Balance System was used to assess static standing balance, word-list and text reading tasks were used to measure reading proficiency. The Behavioural Assessment System for Children - Parent Rating Scale was used to assess attention-deficit-hyperactivity disorder, the Wechsler Intelligence Scale for Children was used to assess cognitive functioning, and the Movement Assessment Battery for Children was used to measure motor functioning.

RESULTS

Balance (F((1,177)) =4.82; p=0.029; =0.027) and reading (F((1,176)) =11.95; p=0.001; =0.064) problems were more common in the at-risk group than in the comparison group. Furthermore, attention, hyperactivity, IQ, and motor functioning were not related to balance problems. However, attention (F((1,154)) =10.80; p=0.001; =0.066) and IQ (F((1,170)) =22.08; p<0.001; =0.115) were individually connected to reading speed.

INTERPRETATION

Balance problems alone could not produce any differences in reading skills. Instead, both balance problems and reduced reading skills were mainly associated separately with a familial risk of dyslexia. This indicates that there may be a shared genetic mechanism between balance and reading problems.

Striking the right balance: motor difficulties in children and adults with dyslexia

Balance difficulties are an enduring feature of dyslexia research, however results have been inconsistent. We propose that between-study heterogeneity may be attributable to variability in balance tasks, balance measurement, participant age, and inclusion of comorbid disorders such as ADHD. This study attempted to clarify these issues, employing quantitative, continuous measures of balance and blindfolded balance, and using both adult and child participants without comorbid ADHD. Eighty-seven individuals participated: dyslexic adults (n = 17), matched adult controls (n = 30), dyslexic children (n = 16) and matched child controls (n = 24). The study found significant balance deficits for the child dyslexic group in the eyes-open task and a result approaching significance in the blindfolded task. By contrast, the adult dyslexic group showed significant deficits in the blindfolded task only. This result is interpreted in terms of lack of sensitivity of the non-blindfolded balance task for adults, owing to ceiling effects. This highlights the need for the use of age-appropriate tests, and may explain some of the heterogeneity in the literature. It is concluded that there is a significant incidence of balance difficulties in children and adults with dyslexia, even for those without comorbid attention deficit.

Effects of dyslexia on postural control in adults

Dyslexia has been shown to affect postural control. The aim of the present study was to investigate the difference in postural stability measured as torque variance in an adult dyslexic group (n=14, determined using the Adult Dyslexia Checklist (ADCL) and nonsense word repetition test) and an adult non-dyslexic group (n=39) on a firm surface and on a foam block and with eyes open and eyes closed. Another aim was to investigate the correlation between ADCL scores and postural stability. Findings showed that ADCL scores correlated with torque variance in the anteroposterior direction on foam with eyes closed (p=0.001) and in the lateral direction on the foam surface with eyes closed (p=0.040) and open (p=0.010). General Linear Model analysis showed that high dyslexia scores were associated with increased torque variance (p<0.001). However, we found no significant difference between dyslexics and non-dyslexics, though there were indications of larger torque variance in the dyslexics. The findings suggest that adults with high dyslexic ADCL scores may experience sub-clinical balance deficits. Hence, assessing motor ability and postural control in those with high ADCL scores is motivated.