A test revealing the slow acquisition and the dorsal stream substrate of visuo-spatial perception

Visuospatial Perception in Prematurely Born Children Without Cerebral Palsy or Retinopathy but With Scholar Complaints

In the absence of any complaints in early childhood, preterm children remain more at risk of encountering academic difficulties, but their clinical picture remains not well characterized. We screened visuospatial perception in 70 children born preterm consulting for scholar complaints. Developmental Coordination Disorder (with or without comorbidities) was associated with high prevalence (27%) of impaired perception of spatial relationship. Prematurely born children who obtained no diagnosis of Neuro-Developmental Disorder exhibited a high prevalence (31%) of impaired perception of object magnitude. Regression revealed that low gestational age and fetal growth restriction significantly predicted the magnitude but not the spatial relationship perception.

Alteration of body representation in typical and atypical motor development

Developmental coordination disorder (DCD) impacts the quality of life and ability to perform coordinated actions in 5% of school-aged children. The quality of body representations of individuals with DCD has been questioned, but never assessed. We hypothesize that children with DCD have imprecise body representations in the sensory and motor domains. Twenty neurotypical children, seventeen children with DCD (8-12 years old) and twenty neurotypical adults (25-45 years old) performed both sensory and motor body representation tasks: a limb identification and a limb movement task. We observed lower accuracy in the sensory task but not in the motor task. In both tasks, we observe a larger amplitude of errors, or synkinesis, in children with DCD than in neurotypical children. In neurotypical children, accuracy was lower than in neurotypical adults in the motor and sensory task, and the amplitude of sensory errors and synkinesis was higher than in neurotypical adults. Using a linear regression model, we showed that sensory accuracy is a good predictor of synkinesis production, and that synkinesis production is a good predictor of sensory accuracy, as can be expected by the perception-action loop. Results support the hypothesis of an imprecision of body representation in DCD. We suggest that this imprecision arises from noise in the body representation used at the level of internal models of action. Future studies may assess whether slower plasticity of body representations, initial imprecision, or both may account for this observation. At the clinical level, prevention strategies targeting body representation in early childhood are strategically important to limit such impairments. RESEARCH HIGHLIGHTS: Body representation is impaired in children with DCD and has a significant cost in terms of the accuracy of sensory identification of body parts and associated movements. Inaccuracies in the body representation measured in perception and in action (error amplitude and synkinesis) are related in both NT children and adults. In typical development, we provide evidence of a strong link between body schema and body image.

Toward the characterization of a visual form of developmental dyslexia: Reduced visuo-attentional capacity for processing multiple stimuli made of separable features

Some dyslexics cannot process multiple letters simultaneously. It has been argued that this reduced visuo-attentional (VA) letter span could result from poor reading ability and experience. Here, moving away from reading context, we showed that dyslexic group exhibited slower visual search than normal readers group for "symbols", defined as graphic stimuli made up of separable visual features, but not for filled objects. Slowness in symbol visual search was explained by reduced VA field and atypical ocular behaviour when processing those letter-like stimuli and was associated with reduced VA letter span and impaired elementary visuo-spatial perception. Such a basic visual search deficit can hardly be attributed to poor reading ability and experience. Moreover, because it is specific to letter-like stimuli (i.e., "symbols"), it can specifically hinder reading acquisition. Symbol visual search can easily be tested in the pre-reading phase, opening up prospects for early risk detection and prevention of VA dyslexia.

Role of the Dorsal Posterior Parietal Cortex in the Accurate Perception of Object Magnitude in Peripheral Vision

Following superior parietal lobule and intraparietal sulcus (SPL-IPS) damage, optic ataxia patients underestimate the distance of objects in the ataxic visual field such that they produce hypometric pointing errors. The metrics of these pointing errors relative to visual target eccentricity fit the cortical magnification of central vision. The SPL-IPS would therefore implement an active “peripheral magnification” to match the real metrics of the environment for accurate action. We further hypothesized that this active compensation of the central magnification by the SPL-IPS contributes to actual object’ size perception in peripheral vision. Three optic ataxia patients and 10 age-matched controls were assessed in comparing the thickness of two rectangles flashed simultaneously, one in central and another in peripheral vision. The bilateral optic ataxia patient exhibited exaggerated underestimation bias and uncertainty compared to the control group in both visual fields. The two unilateral optic ataxia patients exhibited a pathological asymmetry between visual fields: size perception performance was affected in their contralesional peripheral visual field compared to their healthy side. These results demonstrate that the SPL-IPS contributes to accurate size perception in peripheral vision.

Elementary visuospatial perception deficit in children with neurodevelopmental disorders

AIM

To assess the prevalence of elementary visuospatial perception (EVSP) deficit in children with neurodevelopmental disorders.

METHOD

Using a screening test designed and validated to measure dorsal EVSP ability, 168 children (122 males, 46 females; mean age 10y [SD 1y 10mo], range 4y 8mo-16y 4mo) diagnosed with developmental coordination disorder (DCD), specific learning disorder (SLD), attention-deficit/hyperactivity disorder (ADHD), and/or oral language disorder were compared with a group of 184 typically developing children. We also tested 14 children with binocular vision dysfunction and no neurodevelopmental disorder.

RESULTS

Children with SLD scored below the interquartile range of typically developing children as frequently (59%) as children with DCD, but only 5% were severely impaired (i.e. scored as outliers). Children with DCD were the most severely impaired (22% of outliers), even more so when they exhibited a co-occuring disorder. Children with language disorder and those with binocular vision dysfunction scored similarly to the group of typically developing children.

INTERPRETATION

These results confirm the importance of assessing EVSP in the clinical evaluation of children with neurodevelopmental disorders, in particular those presenting with DCD or SLD. What this paper adds More than half of children with developmental coordination disorder (DCD) scored below the normal interquartile range on the elementary visuospatial perception (EVSP) test. More than half of children with specific learning disorder (SLD) scored below the normal interquartile range on the EVSP test. Twenty-two percent of children with DCD performed as outliers on the EVSP test. Children with language disorder and those with binocular vision dysfunction scored similarly to typically developing children.

[Long term outcome of perinatal stroke]

Neonatal Arterial Ischemic Stroke (NAIS) affects 6-17 newborns on 100 000-birth term neonates, most of these children keeping long-term motor and cognitive impairments. Based on a literature review, the objectives of this paper are to describe motor and cognitive outcomes after a NAIS and to propose a consensual monitoring of these children to improve their management. About 30 % of children after a NAIS will develop a unilateral cerebral palsy requiring a management by a team with expertise in physical medicine and rehabilitation. Unlike adults, especially after a left NAIS, children will not present aphasia but between 50 and 90 % will present disorders of speech and language in expression and/or reception. After NAIS, the global intellectual efficiency is usually preserved except when the size of the lesion is very important or when severe epilepsy occurs. Several studies are also in favor of vulnerability in visuospatial functions. To quantify impairments, activity limitations and participation restrictions resulting from this NAIS, early and at least yearly evaluations with reliable tools must be carried out systematically until puberty. A multidisciplinary team with a longitudinal follow-up, in all the different developmental dimensions, must conduct these evaluations in term of motor skills, cognitive impairment, behavior, autonomy, quality of life, and participation. Consequences on family functioning need to be evaluate in order to help children and family coping with this event.

Language disorders in victims of domestic violence in children's homes

Studies that deal with child maltreatment have become relevant during these past years. One important aspect to consider is the impact of maltreatment on the cognitive functioning and more precisely on language. Our objective is to analyze the different components in the comprehension and production of language in children victims of domestic abuse in Childreńs Homes.

PARTICIPANTS

The sample consists of 104 participants divided in two groups. A group of children who have just been institutionalized due to domestic abuse (VG) (Age: 8 years 2 months with a standard deviation of 1, 5 years) without previous treatment; a group of comparison (CG) made up by children who have not been victim of domestic violence (Age: 8 years 6 months with a standard deviation of 2 years and a month), with similar characteristics of gender, age and schooling.

MATERIAL

The Child Neuropsychological Assessment by Matute, Rosselli, Ardila and Ostrosky (2007) was applied. This test includes metalinguistic, oral and written comprehension and expression skills.

RESULTS

The VG group showed low scores in all components of the analyzed language with exception to the discourse, syllable and non-word dictation compared to the CG children.

CONCLUSIONS

The alterations of the language observed in these children semantic suggest a lack of consolidation of phonological coding and a low use of code. From our findings an early language evaluation in these children can be of especial interest to apply timely intervention programs with the aim of diminishing the impact caused by domestic violence on school failure which is a frequent trait in these children.

Basic visual perceptual processes in children with typical development and cerebral palsy: The processing of surface, length, orientation, and position

The present study aims to assess how the processing of basic visual perceptual (VP) components (length, surface, orientation, and position) develops in typically developing (TD) children (n = 215, 4-14 years old) and adults (n = 20, 20-25 years old), and in children with cerebral palsy (CP) (n = 86, 5-14 years old) using the first four subtests of the Battery for the Evaluation of Visual Perceptual and Spatial processing in children. Experiment 1 showed that these four basic VP processes follow distinct developmental trajectories in typical development. Experiment 2 revealed that children with CP present global and persistent deficits for the processing of basic VP components when compared with TD children matched on chronological age and nonverbal reasoning abilities.

Optic ataxia: beyond the dorsal stream cliché

This chapter reviews clinical and scientific approaches to optic ataxia. This double historic track allows us to address important issues such as the link between Bálint syndrome and optic ataxia, the alleged double dissociation between optic ataxia and visual agnosia, and the use of optic ataxia to argue for a specific vision-for-action occipitoposterior parietal stream. Clinical cases are described and reveal that perceptual deficits have been long shown to accompany ataxia. Importantly, the term ataxia appears to be misleading as patients exhibit a combination of visual and nonvisual perceptual, attentional, and visuomotor guidance deficits, which are confirmed by experimental approaches. Three major features of optic ataxia are described. The first is a spatial feature whereby the deficits exhibited by patients appear to be specific to peripheral vision, akin to the field effect. Visuomotor field examination allows us to quantify this deficit and reveals that it consists of a highly reliable retinocentric hypometria. The third is a temporal feature whereby these deficits are exacerbated under temporal constraints, i.e., when attending to dynamic stimuli. These two aspects combine in a situation where patients have to quickly respond to a target presented in peripheral vision that is experimentally displaced upon movement onset. In addition to the field effect, a hand effect can be described in conditions where the hand is not visible. Spatial and temporal aspects as well as field and hand effects may rely on several posterior parietal modules that remain to be precisely identified both anatomically and functionally. It is concluded that optic ataxia is not a visuomotor deficit and there is no dissociation between perception and action capacities in optic ataxia, hence a fortiori no double dissociation between optic ataxia and visual agnosia. Future directions for understanding the basic pathophysiology of optic ataxia are proposed.

Development of Visuospatial Attention in Typically Developing Children

The aim of the present study is to investigate the development of visuospatial attention in typically developing children and to propose reference values for children for the following six visuospatial attention tests: star cancellation, Ogden figure, reading test, line bisection, proprioceptive pointing and visuo-proprioceptive pointing. Data of 159 children attending primary or secondary school in the Fédération Wallonie Bruxelles (Belgium) were analyzed. Results showed that the children's performance on star cancellation, Ogden figure and reading test improved until the age of 13 years, whereas their performance on proprioceptive pointing, visuo-proprioceptive pointing and line bisection was stable with increasing age. These results suggest that the execution of different types of visuospatial attention tasks are not following the same developmental trajectories. This dissociation is strengthened by the lack of correlation observed between tests assessing egocentric and allocentric visuospatial attention, except for the star cancellation test (egocentric) and the Ogden figure copy (ego- and allocentric). Reference values are proposed that may be useful to examine children with clinical disorders of visuospatial attention.

Reachability judgement in optic ataxia: Effect of peripheral vision on hand and target perception in depth

The concept of peripersonal space was first proposed by Rizzolatti, Scandolara, Matelli, and Gentilucci (1981), who introduced the term to highlight the close links between somatosensory and visual processing for stimuli close to the body and suggested that this near-body space could in fact be characterized as an action space (Rizzolatti, Fadiga, Fogassi, & Gallese, 1997). Supporting this idea, patients with right hemisphere lesions have been described as impaired in performing actions towards objects and in perceiving their location - but only when the objects were presented within arm's reach (Bartolo, Carlier, Hassaini, Martin, & Coello, 2014; Brain, 1941). Whether the deficit of optic ataxia patients in processing target locations for action has an effect on the representation of peripersonal space has never been explored. The present study highlights optic ataxia patients' specific difficulties in processing hand-to-target distances in a motor task and in a perceptual task requiring identification of what is reachable in the visual environment. The difficulties are especially evident when both the target and the hand are perceived in the visual periphery. Indeed, when patient I.G. was able to fixate the target, her reaching accuracy and her perception of reachable space both largely improved. Furthermore, the difficulties were enhanced when the hand and the target were both in the lower visual field (in a fixed-far condition vs a fixed-near condition). This novel up-down dimension of optic ataxia fits with the larger representation of the lower visual field in the posterior parietal cortex (Pitzalis et al., 2013; Previc, 1990).

Two Visual Pathways in Primates Based on Sampling of Space: Exploitation and Exploration of Visual Information

Evidence is strong that the visual pathway is segregated into two distinct streams—ventral and dorsal. Two proposals theorize that the pathways are segregated in function: The ventral stream processes information about object identity, whereas the dorsal stream, according to one model, processes information about either object location, and according to another, is responsible in executing movements under visual control. The models are influential; however recent experimental evidence challenges them, e.g., the ventral stream is not solely responsible for object recognition; conversely, its function is not strictly limited to object vision; the dorsal stream is not responsible by itself for spatial vision or visuomotor control; conversely, its function extends beyond vision or visuomotor control. In their place, we suggest a robust dichotomy consisting of a ventral stream selectively sampling high-resolution/focal spaces, and a dorsal stream sampling nearly all of space with reduced foveal bias. The proposal hews closely to the theme of embodied cognition: Function arises as a consequence of an extant sensory underpinning. A continuous, not sharp, segregation based on function emerges, and carries with it an undercurrent of an exploitation-exploration dichotomy. Under this interpretation, cells of the ventral stream, which individually have more punctate receptive fields that generally include the fovea or parafovea, provide detailed information about object shapes and features and lead to the systematic exploitation of said information; cells of the dorsal stream, which individually have large receptive fields, contribute to visuospatial perception, provide information about the presence/absence of salient objects and their locations for novel exploration and subsequent exploitation by the ventral stream or, under certain conditions, the dorsal stream. We leverage the dichotomy to unify neuropsychological cases under a common umbrella, account for the increased prevalence of multisensory integration in the dorsal stream under a Bayesian framework, predict conditions under which object recognition utilizes the ventral or dorsal stream, and explain why cells of the dorsal stream drive sensorimotor control and motion processing and have poorer feature selectivity. Finally, the model speculates on a dynamic interaction between the two streams that underscores a unified, seamless perception. Existing theories are subsumed under our proposal.

The Pointing Errors in Optic Ataxia Reveal the Role of "Peripheral Magnification" of the PPC

Interaction with visual objects in the environment requires an accurate correspondence between visual space and its internal representation within the brain. Many clinical conditions involve some impairment in visuo-motor control and the errors created by the lesion of a specific brain region are neither random nor uninformative. Modern approaches to studying the neuropsychology of action require powerful data-driven analyses and error modeling in order to understand the function of the lesioned areas. In the present paper we carried out mixed-effect analyses of the pointing errors of seven optic ataxia patients and seven control subjects. We found that a small parameter set is sufficient to explain the pointing errors produced by unilateral optic ataxia patients. In particular, the extremely stereotypical errors made when pointing toward the contralesional visual field can be fitted by mathematical models similar to those used to model central magnification in cortical or sub-cortical structure(s). Our interpretation is that visual areas that contain this footprint of central magnification guide pointing movements when the posterior parietal cortex (PPC) is damaged and that the functional role of the PPC is to actively compensate for the under-representation of peripheral vision that accompanies central magnification. Optic ataxia misreaching reveals what would be hand movement accuracy and precision if the human motor system did not include elaborated corrective processes for reaching and grasping to non-foveated targets.

Reliability and validity of the Leuven Perceptual Organization Screening Test (L-POST)

Neuropsychological tests of visual perception mostly assess high-level processes like object recognition. Object recognition, however, relies on distinct mid-level processes of perceptual organization that are only implicitly tested in classical tests. Furthermore, the psychometric properties of the existing instruments are limited. To fill this gap, the Leuven perceptual organization screening test (L-POST) was developed, in which a wide range of mid-level phenomena are measured in 15 subtests. In this study, we evaluated reliability and validity of the L-POST. Performance on the test is evaluated relative to a norm sample of more than 1,500 healthy control participants. Cronbach's alpha of the norm sample and test-retest correlations for 20 patients provide evidence for adequate reliability of L-POST performance. The convergent and discriminant validity of the test was assessed in 40 brain-damaged patients, whose performance on the L-POST was compared with standard clinical tests of visual perception and other measures of cognitive function. The L-POST showed high sensitivity to visual dysfunction and decreased performance was specific to visual problems. In conclusion, the L-POST is a reliable and valid screening test for perceptual organization. It offers a useful online tool for researchers and clinicians to get a broader overview of the mid-level processes that are preserved or disrupted in a given patient.

Decoupled visually-guided reaching in optic ataxia: differences in motor control between canonical and non-canonical orientations in space

Guiding a limb often involves situations in which the spatial location of the target for gaze and limb movement are not congruent (i.e. have been decoupled). Such decoupled situations involve both the implementation of a cognitive rule (i.e. strategic control) and the online monitoring of the limb position relative to gaze and target (i.e. sensorimotor recalibration). To further understand the neural mechanisms underlying these different types of visuomotor control, we tested patient IG who has bilateral caudal superior parietal lobule (SPL) damage resulting in optic ataxia (OA), and compared her performance with six age-matched controls on a series of center-out reaching tasks. The tasks comprised 1) directing a cursor that had been rotated (180° or 90°) within the same spatial plane as the visual display, or 2) moving the hand along a different spatial plane than the visual display (horizontal or para-sagittal). Importantly, all conditions were performed towards visual targets located along either the horizontal axis (left and right; which can be guided from strategic control) or the diagonal axes (top-left and top-right; which require on-line trajectory elaboration and updating by sensorimotor recalibration). The bilateral OA patient performed much better in decoupled visuomotor control towards the horizontal targets, a canonical situation in which well-categorized allocentric cues could be utilized (i.e. guiding cursor direction perpendicular to computer monitor border). Relative to neurologically intact adults, IG's performance suffered towards diagonal targets, a non-canonical situation in which only less-categorized allocentric cues were available (i.e. guiding cursor direction at an off-axis angle to computer monitor border), and she was therefore required to rely on sensorimotor recalibration of her decoupled limb. We propose that an intact caudal SPL is crucial for any decoupled visuomotor control, particularly when relying on the realignment between vision and proprioception without reliable allocentric cues towards non-canonical orientations in space.