Expressive versus receptive language skills in specific reading disorder

Despite ample research into the language skills of children with specific reading disorder no studies so far have investigated whether there may be a difference between expressive and receptive language skills in this population. Yet, neuro-anatomical models would predict that children who have specific reading disorder which is not associated with movement or attention difficulties, would have lower receptive language skills than expressive. This study investigates the difference between expressive and receptive language skills in a sample of 17 children with specific reading difficulty aged between 7 and 12 years. They were administered a battery of two receptive and two expressive language measures. The results showed that as the neuro-anatomical model would predict, the children scored significantly lower on tests of receptive than on tests of expressive language skills.

Binocular coordination of the eyes during reading

Saccadic eye movements and fixations are the behavioral means by which we visually sample text during reading. Human oculomotor control is governed by a complex neurophysiological system involving the brain stem, superior colliculus, and several cortical areas [1, 2]. A very widely held belief among researchers investigating primate vision is that the oculomotor system serves to orient the visual axes of both eyes to fixate the same target point in space. It is argued that such precise positioning of the eyes is necessary to place images on corresponding retinal locations, such that on each fixation a single, nondiplopic, visual representation is perceived [3]. Vision works actively through a continual sampling process involving saccades and fixations [4]. Here we report that during normal reading, the eyes do not always fixate the same letter within a word. We also demonstrate that saccadic targeting is yoked and based on a unified cyclopean percept of a whole word since it is unaffected if different word parts are delivered exclusively to each eye via a dichoptic presentation technique. These two findings together suggest that the visual signal from each eye is fused at a very early stage in the visual pathway, even when the fixation disparity is greater than one character (0.29 deg), and that saccade metrics for each eye are computed on the basis of that fused signal.

Receding and disparity cues aid relaxation of accommodation

Purpose. Accommodation can mask hyperopia and reduce the accuracy of non-cycloplegic refraction. It is, therefore, important to minimize accommodation to obtain a measure of hyperopia as accurate as possible. To characterize the parameters required to measure the maximally hyperopic error using photorefraction, we used different target types and distances to determine which target was most likely to maximally relax accommodation and thus more accurately detect hyperopia in an individual. Methods. A PlusoptiX SO4 infra-red photorefractor was mounted in a remote haploscope which presented the targets. All participants were tested with targets at four fixation distances between 0.3 and 2 m containing all combinations of blur, disparity, and proximity/looming cues. Thirty-eight infants (6 to 44 weeks) were studied longitudinally, and 104 children [4 to 15 years (mean 6.4)] and 85 adults, with a range of refractive errors and binocular vision status, were tested once. Cycloplegic refraction data were available for a sub-set of 59 participants spread across the age range. Results. The maximally hyperopic refraction (MHR) found at any time in the session was most frequently found when fixating the most distant targets and those containing disparity and dynamic proximity/looming cues. Presence or absence of blur was less significant, and targets in which only single cues to depth were present were also less likely to produce MHR. MHR correlated closely with cycloplegic refraction (r = 0.93, mean difference 0.07 D, p = n.s., 95% confidence interval +/-<0.25 D) after correction by a calibration factor. Conclusions. Maximum relaxation of accommodation occurred for binocular targets receding into the distance. Proximal and disparity cues aid relaxation of accommodation to a greater extent than blur, and thus non-cycloplegic refraction targets should incorporate these cues. This is especially important in screening contexts with a brief opportunity to test for significant hyperopia. MHR in our laboratory was found to be a reliable estimation of cycloplegic refraction. (Optom Vis Sci 2009;86:1276-1286)

A novel experimental method for measuring vergence and accommodation responses to the main near visual cues in typical and atypical groups

Binocular disparity, blur, and proximal cues drive convergence and accommodation. Disparity is considered to be the main vergence cue and blur the main accommodation cue. We have developed a remote haploscopic photorefractor to measure simultaneous vergence and accommodation objectively in a wide range of participants of all ages while fixating targets at between 0.3 and 2 m. By separating the three main near cues, we can explore their relative weighting in three-, two-, one-, and zero-cue conditions. Disparity can be manipulated by remote occlusion; blur cues manipulated by using either a Gabor patch or a detailed picture target; looming cues by either scaling or not scaling target size with distance. In normal orthophoric, emmetropic, symptom-free, naive visually mature participants, disparity was by far the most significant cue to both vergence and accommodation. Accommodation responses dropped dramatically if disparity was not available. Blur only had a clinically significant effect when disparity was absent. Proximity had very little effect. There was considerable interparticipant variation. We predict that relative weighting of near cue use is likely to vary between clinical groups and present some individual cases as examples. We are using this naturalistic tool to research strabismus, vergence and accommodation development, and emmetropization.

Gender differences in early accommodation and vergence development

A remote haploscopic photorefractor was used to assess objective binocular vergence and accommodation responses in 157 full-term healthy infants aged 1-6 months while fixating a brightly coloured target moving between fixation distances at 2, 1, 0.5 and 0.33 m. Vergence and accommodation response gain matured rapidly from 'flat' neonatal responses at an intercept of approximately 2 dioptres (D) for accommodation and 2.5 metre angles(MA) for vergence, reaching adult-like values at 4 months. Vergence gain was marginally higher in females (p = 0.064), but accommodation gain (p = 0.034) was higher and accommodative intercept closer to zero (p = 0.004) in males in the first 3 months as they relaxed accommodation more appropriately for distant targets. More females showed flat accommodation responses (p = 0.029). More males behaved hypermetropically in the first two months of life, but when these hypermetropic infants were excluded from the analysis, the gender difference remained. Gender differences disappeared after three months. Data showed variable responses and infants could behave appropriately and simultaneously on both, neither or only one measure at all ages. If accommodation was appropriate (gain between 0.7 and 1.3; r(2) > 0.7) but vergence was not, males over- and under-converged equally, while the females who accommodated appropriately were more likely to overconverge (p = 0.008). The apparent earlier maturity of the male accommodative responses may be due to refractive error differences but could also reflect gender-specific male preference for blur cues while females show earlier preference for disparity, which may underpin the earlier emerging, disparity dependent, stereopsis and full vergence found in females in other studies.

Can misalignments in typical infants be used as a model for infantile esotropia?

PURPOSE. To investigate the nature of early ocular misalignments in human infants to determine whether they can provide insight into the etiology of esotropia and, in particular, to examine the correlates of misalignments. METHODS. A remote haploscopic photorefraction system was used to measure accommodation and vergence in 146 infants between 0 and 12 months of age. Infants underwent photorefraction immediately after watching a target moving between two of five viewing distances (25, 33, 50, 100, and 200 cm). In some instances, infants were tested in two conditions: both eyes open and one eye occluded. The resultant data were screened for instances of large misalignments. Data were assessed to determine whether accommodative, retinal disparity, or other cues were associated with the occurrence of misalignments. RESULTS. The results showed that there was no correlation between accommodative behavior and misalignments. Infants were more likely to show misalignments when retinal disparity cues were removed through occlusion. They were also more likely to show misalignments immediately after the target moved from a near to a far position in comparison to far-to-near target movement. DISCUSSION. The data suggest that the prevalence of misalignments in infants of 2 to 3 months of age is decreased by the addition of retinal disparity cues to the stimulus. In addition, target movement away from the infant increases the prevalence of misalignments. These data are compatible with the notion that misalignment are caused by poor sensitivity to targets moving away from the infant and support the theory that some forms of strabismus could be related to failure in a system that is sensitive to the direction of motion.

Mind-reading difficulties in the siblings of people with Asperger's syndrome: evidence for a genetic influence in the abnormal development of a specific cognitive domain

Background: Previous research suggests that the phenotype associated with Asperger's syndrome (AS) includes difficulties in understanding the mental states of others, leading to difficulties in social communication and social relationships. It has also been suggested that the first-degree relatives of those with AS can demonstrate similar difficulties, albeit to a lesser extent. This study examined 'theory of mind' (ToM) abilities in the siblings of children with AS relative to a matched control group. Method: 2 7 children who had a sibling with AS were administered the children's version of the 'Eyes Test'(Baron-Cohen, Wheelwright, Stone, & Rutherford, 1999). The control group consisted of 27 children matched for age, sex, and a measure of verbal comprehension, and who did not have a family history of AS/autism. Results: A significant difference was found between the groups on the Eyes Test, the 'siblings' group showing a poorer performance on this measure of social cognition. The difference was more pronounced among female siblings. Discussion: These results are discussed in terms of the familial distribution of a neuro-cognitive profile associated with AS, which confers varying degrees of social handicap amongst first-degree relatives. The implication of this finding with regard to the autism/AS phenotype is explored, with some discussion of why this neuro-cognitive profile (in combination with corresponding strengths) may have an evolutionary imperative.

Involuntary inhibition of movement initiation alters oculomotor competition resolution

Identifying a stimulus as the target for a goal-directed movement involves inhibiting competing responses. Separable inhibitory interconnections bias local competition to ensure only one stimulus is selected and to alter movement initiation. Behavioural evidence of these inhibitory processes comes from the effects of distracters on oculomotor landing positions and saccade latencies. Here, we investigate the relationship between these two sources of inhibition. Targets were presented with or without close and remote distracters. In separate experiments the possible position and identity of the target and distracters were manipulated. In all cases saccade landing position was found to be less affected by the presence of the close distracter when remote distracters were also present. The involuntary increase in the latency of saccade initiation caused by the presence of the remote distracters alters the state of competitive processes involved in selecting the saccade target thus changing its landing position.

Attention processes in children with movement difficulties, reading difficulties or both

Reading difficulties (RD) and movement difficulties (MD) co-occur more often in clinical populations than expected for independent disorders. In this study, we investigated the pattern of association between attentional processes, RD and MD in a population of 9 year old school children. Children were screened to identify index groups with RD, MD or both, plus a control group. These groups were then tested on a battery of cognitive attention assessments (TEA-Ch). Results confirmed that the occurrence of RD and MD was greater than would be predicted for independent disorders. Additionally, children with MD, whether or not combined with RD, had poor performance on all attention measures when compared with typically developing children. Children with RD only, were no poorer on measures of attention than typical children. The results are discussed with respect to approaches proposed to account for the co-occurrence of disorders.

Case study: object and ground point separation on a river bank using airborne based LIDAR data

In the past decade, airborne based LIght Detection And Ranging (LIDAR) has been recognised by both the commercial and public sectors as a reliable and accurate source for land surveying in environmental, engineering and civil applications. Commonly, the first task to investigate LIDAR point clouds is to separate ground and object points. Skewness Balancing has been proven to be an efficient non-parametric unsupervised classification algorithm to address this challenge. Initially developed for moderate terrain, this algorithm needs to be adapted to handle sloped terrain. This paper addresses the difficulty of object and ground point separation in LIDAR data in hilly terrain. A case study on a diverse LIDAR data set in terms of data provider, resolution and LIDAR echo has been carried out. Several sites in urban and rural areas with man-made structure and vegetation in moderate and hilly terrain have been investigated and three categories have been identified. A deeper investigation on an urban scene with a river bank has been selected to extend the existing algorithm. The results show that an iterative use of Skewness Balancing is suitable for sloped terrain.

Optimization algorithms in FMRF model-based segmentation for LIDAR data and co-registered bands

In this paper, a fuzzy Markov random field (FMRF) model is used to segment land-objects into free, grass, building, and road regions by fusing remotely, sensed LIDAR data and co-registered color bands, i.e. scanned aerial color (RGB) photo and near infra-red (NIR) photo. An FMRF model is defined as a Markov random field (MRF) model in a fuzzy domain. Three optimization algorithms in the FMRF model, i.e. Lagrange multiplier (LM), iterated conditional mode (ICM), and simulated annealing (SA), are compared with respect to the computational cost and segmentation accuracy. The results have shown that the FMRF model-based ICM algorithm balances the computational cost and segmentation accuracy in land-cover segmentation from LIDAR data and co-registered bands.