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Steroscopic discrimination in infants.
The ability to make discrimiations of binocular disparity was investigated in 2-month-old infnats by two methods: (a)fixation preference between patterns differing in the disparity they contained, and (b)recovery from habituation of high-amplitude sucking when there was a change in disparity in the visual reinforcer. The stimuli were random-dot steregrams. The results for both mthods indicated that at least some infants of this age could perform steroscopic discriminations and that both techniques were feasible for development for longitudinal studies of steroscopic vision.
Non-cycloplegic refractive screening can identify infants whose visual outcome at 4 years is improved by spectacle correction.
The Second Cambridge Population Infant Vision Screening Programme using the VPR-1 videorefractor without cycloplegia was undertaken in order to identify those infants with refractive errors who were potentially amblyogenic or strabismogenic. Infants identified at eight months were entered into a control trial of treatment with partial spectacle correction and underwent a long-term follow-up that monitored a wide range of visual, visuoperceptual, visuocognitive, visuomotor, linguistic and social development. In the present paper, the authors report on the outcome measures of visual acuity and strabismus. Poor acuity was defined as a best-corrected acuity of 6/12 or worse on crowded letters or 6/9 or worse on single letters, at age 4 years. Acuity was measured in 79 infants who were significantly hyperopic and/or anisometropic at 11-12 months of age, 23 who showed hyperopia of +3D but less than +3.5D, 196 control subjects, 14 controls with refractive errors, and 126 others who showed an accommodative lag on screening but were not significantly hyperopic on first retinoscopy. There was a poorer acuity outcome in the untreated group of hyperopes compared to controls (p < 0.0001) and to the children who were compliant in spectacle wear (p < 0.001) or who were prescribed spectacles (p < 0.05). Children who were significantly hyperopic at eight months were also more likely to be strabismic by 5.5 years compared to the emmetropic control group (p < 0.001). However, the present study did not find a significant difference in the incidence of strabismus between corrected and uncorrected hyperopic infants. Children who were not refractively corrected for significant hyperopia were four times more likely to have poor acuity at 5.5 years than infants who wore their hyperopic correction, supporting the findings of the First Cambridge Population Infant Vision Screening Programme.
A test battery of child development for examining functional vision (ABCDEFV).
A battery of 22 tests is described, intended to give an integrated assessment of children's functional visual capacities between birth and four years of age. As well as sensory visual measures such as acuity, visual fields and stereopsis, the battery is intended to tap a range of perceptual, motor, spatial and cognitive aspects of visual function. Tests have been drawn from practice in ophthalmology and orthoptics, vision research, paediatric neurology, and developmental psychology to give an overall view of children's visual competences for guidance in diagnosis, further investigation, management and rehabilitation of children with developmental disorders. 'Core vision tests' require no motoric capacities beyond saccadic eye movements or linguistic skills and so assess basic visual capacities in children of any age. 'Additional tests' have age-specific requirements and are designed to pinpoint specific deficits in the perceptual, visuo-motor and spatio-cognitive domains. Normative data are reported on nine age groups between 0-6 weeks and 31-36 months, each including 32-43 typically developing children. Pass/fail criteria for each test are defined. These data allow the selection of a subset of tests for each age group which are passed by at least 85% of normally developing children, and so are appropriate for defining normal development. The normalized battery has been applied to a range of at-risk and clinical groups. Aspects of children's visual performance are discussed in relation to neurobiological models of visual development.
Optics of photorefraction: orthogonal and isotropic methods.
Analysis of the optics of photorefractively computed ray tracing shows that, for short camera-to-subject distances, the function relating image size to defocus of the eye is not symmetrical for errors of focus in front of and behind the camera. This asymmetry is exploited in the new method of isotropic photorefraction, in which the supplementary cylinder lenses of the original orthogonal photorefractors are replaced by defocusing of the camera lens itself. By comparing photographs taken with the camera focused in front of and behind the subject, the sign of the eyes' defocus (myopic or hyperopic relative to the camera) can be determined. The axis of any astigmatism is readily apparent as the direction in which the photorefractive images are elongated. The method is well adapted for the refractive screening of infants and young children.
Asymmetrical cortical processing of radial expansion/contraction in infants and adults.
We report asymmetrical cortical responses (steady-state visual evoked potentials) to radial expansion and contraction in human infants and adults. Forty-four infants (22 3-month-olds and 22 4-month-olds) and nine adults viewed dynamic dot patterns which cyclically (2.1 Hz) alternate between radial expansion (or contraction) and random directional motion. The first harmonic (F1) response in the steady-state VEP response must arise from mechanisms sensitive to the global radial motion structure. We compared F1 amplitudes between expansion-random and contraction-random motion alternations. F1 amplitudes for contraction were significantly larger than those for expansion for the older infants and adults but not for the younger infants. These results suggest that the human cortical motion mechanisms have asymmetrical sensitivity for radial expansion vs. contraction, which develops at around 4 months of age. The relation between development of sensitivity to radial motion and cortical motion mechanisms is discussed.
Motion- and orientation-specific cortical responses in infancy.
During the first 3 months, infants develop visual evoked potential (VEP) responses that are signatures of cortical orientation-selectivity and directional motion selectivity. Orientation-specific cortical responses develop in early infancy. This study compared these responses directly in the same infants, to investigate whether the later appearance of direction selectivity was intrinsic, or a function of the spatio-temporal characteristics of the stimuli used. Steady-state orientation-reversal (OR-) VEPs and direction-reversal (DR-) VEPs were recorded in infants aged 4-18 weeks. DR-VEPs were elicited with random pixel patterns and with gratings spatially similar to those used for OR-VEPs, at velocities of 5.5 and 11 deg/s, and reversal rates of 2 and 4 reversals/s. Infants throughout the age range showed significant responses to orientation-reversal. Direction-reversal responses appeared in less than 25% of infants under 7 weeks of age, rising to 80% or more at 11-13 weeks, whether tested with dots or gratings and for both speeds and reversal rates. However, 2 reversals/s elicits the DR-VEP on average about 2 weeks earlier than 4 reversal/s stimulation. We conclude that human cortical direction selectivity develops separately from orientation-selectivity and emerges at a later age, even with tests that are designed to optimise the former.
Neonatal cerebral infarction and visual function at school age.
OBJECTIVE: To assess various aspects of visual function at school age in children with neonatal cerebral infarction. PATIENTS AND METHODS: Sixteen children born at term, who had cerebral infarction of perinatal onset on neonatal magnetic resonance imaging (MRI) were assessed using a battery of visual tests. This included measures of crowding acuity (Cambridge Crowding Cards), stereopsis (TNO test), and visual fields. The results of the visual assessment were compared with the type and the extent of the lesion observed on neonatal MRI. RESULTS: Only six of the 16 children (28%) had some abnormalities of visual function on these tests. Visual abnormalities were more common in children with more extensive lesions involving the main branch of the middle cerebral artery and were less often associated with lesions in the territory of one of the cortical branches of the middle cerebral artery. The presence of visual abnormalities was not always associated with the involvement of optic radiations or occipital primary visual cortex. Abnormal visual fields were only found in children who also developed hemiplegia. CONCLUSIONS: Abnormality of visual function is not common in children who had neonatal infarction and, when present, tends to be associated with hemiplegia and more extensive lesions.
Normal emmetropization in infants with spectacle correction for hyperopia.
PURPOSE: The development of emmetropic refraction is known to be under visual control. Does partial spectacle correction of infants' refractive errors, which has been shown to have beneficial effects in reducing strabismus and amblyopia, impede emmetropization? The purpose of the present study was to perform the first longitudinal controlled trial to investigate this question in human subjects. METHODS: Children identified as having significant hyperopia in a population screening program at age 8 to 9 months were assigned to treated (partial spectacle correction) or untreated groups. A control group of infants with no significant refractive errors at screening was also recruited. Measurements of retinoscopic refraction under cycloplegia were taken at 4- to 6-month intervals up to the age of 36 months, and changes in refraction of 148 subjects were analyzed longitudinally. RESULTS: Refractive error decreased toward low hyperopic values between 9 and 36 months in both hyperopic groups. By 36 months, this reduction of hyperopia showed no overall difference between children who were treated with partial spectacle correction and those who were not. Despite the improvement, both hyperopic groups' mean refractive error at 36 months remained higher than that of the control group. When infants in all three groups were considered together, the rate of reduction of refractive error was, on average, a linear function of the initial level of hyperopia. CONCLUSIONS: The benefits of spectacle correction for infants with hyperopia can be achieved without impairing the normal developmental regulation of refraction.
The effect of removing visual information on reach control in young children.
Visual information about the hand, the reach space, and a target can all contribute to the control of a reaching movement. When visual information is removed, both feedforward mechanisms (involved in planning the movement) and feedback mechanisms (involved in correcting errors) may be affected. This study looks at how 4- to 5-year-old children use visual information to guide reaching movements. Children reached for a toy object in four conditions--in the light, in the dark while the toy was glowing, and in complete darkness after a 0-s delay and a 4-s delay. When a reach in the glowing condition was compared with a reach in the light, reaches were more curved, had a longer duration, and earlier time-to-peak-velocity than a reach in the light but the number of grasping responses were comparable to in the light condition. When a reach in the two dark conditions (0- and 4-s) was compared with a reach in the light, the number of grasping responses decreased and 14 and 31 % of reaches resulted in a miss, that is, no contact was made with the object. While we did not find any significant kinematic differences between the 0- and 4-s dark conditions, there was a significantly larger number of misses in the 4-s dark condition, suggesting that memory of target position may decay over time. Overall, removing vision of the hand and reach space in the glowing condition appears to affect the planning of a reach (as vision of the hand was not available at reach initiation) and feedback control, while removing vision of the object in the dark conditions has an effect on endpoint response as we found that children experience difficulty retrieving the object in the dark. While young children demonstrate more adult-like reach control (i.e., relatively longer deceleration time, increased reach duration) under reduced feedback conditions, they have difficulty retrieving the object in the dark, particularly after a 4-s delay, and it is possible that mechanisms guiding predictive control and visual memory are still developing.
Uneven integration for perception and action cues in children's working memory.
We examined the development of visual cue integration in a desktop working-memory task using boxes with different visual action cues (opening actions) and perceptual surface cues (colours, monochromatic textures, or images of faces). Children had to recall which box held a hidden toy, based on (a) the action cue, (b) the surface cue, or (c) a conjunction of the two. Results from three experiments show a set of asymmetries in children's integration of action and surface cues. The 18-24-month-olds disregarded colour in conjunction judgements with action; 30-36-month-olds used colour but disregarded texture. Images of faces were not disregarded at either age. We suggest that 18-24-month-olds' disregard of colour, seen previously in reorientation tasks (Hermer & Spelke, 1994), may represent a general phenomenon, likened to uneven integration between the dorsal and ventral streams in early development.
Infant emmetropization: longitudinal changes in refraction components from nine to twenty months of age.
Rapid emmetropization is described in pediatrically normal infants from 9 months of age during the following year. The infants, obtained from various categories of the Cambridge population screening program, provided a broad range of refractive errors. The large group of 254 nonanisometropic infants studied allowed the mean rate of change and dependence on the initial refraction value to be determined. Refraction was measured by cycloplegic retinoscopy. Rapid emmetropization changes occurred in the following refractive components: mean spherical equivalent (MSE), astigmatism magnitude, the horizontal astigmatism component, the infant's most positive meridian, and the infant's most negative meridian. The MSE and astigmatism rates of change (diopters/year), were highly dependent on their respective initial powers (r = -0.61 and r = -0.76). The percentage weighted mean proportional rate of change for MSE was -30% (SE 4%) and for astigmatism magnitude it was -59% (SE 14%). There was much individual variation, with some exhibiting fast emmetropization and others not. The MSE and astigmatism changes, however, were almost independent of each other. The refractive errors of the most positive and most negative meridians emmetropize because they are both derived from the MSE and half the astigmatism. With-the-rule astigmatism was more prevalent than against-the-rule astigmatism at 9 months of age, and with-the-rule astigmatism exhibited a significantly greater proportional rate of change. The relationship of emmetropization and refractive screening is considered. A new component "MOMS" is introduced, the maximum ocular meridional separation, when both eyes are considered. Thus incorporating astigmatism and anisometropia may be a good single indicator of conditions associated with later amblyopia. The almost independent emmetropization of the MSE and astigmatism components is an important result to consider in theories of emmetropization, refractive screening, clinical prescribing, and the evaluation of infants in treatment trials.
Some recent findings on the development of human binocularity: a review.
Evidence on the development of binocular function in infancy is reviewed. (1) Visual evoked potentials (VEP) may be recorded from infants in response to dynamic random dot stimuli which alternate between positive and negative binocular correlation. Such responses can only arise in neurones receiving binocular input. (2) Infants' looking behaviour may be shown to depend on the presence of binocular disparity in the stimulus (either random-dot or line stereograms). Results of these techniques agree that binocular function normally develops initially between 2 and 4 months of age. Our own data using VEP show a median age of first binocular response of 13 weeks but with marked individual variations. Binocular development involves the interplay of sensory interaction and oculomotor coordination, but it is unlikely that alignment of the two eyes is the dominant constraint determining the onset of binocular vision. It is possible, but not yet established, that the detection of binocular correlation may precede the ability to discriminate stereoscopic disparities. Infants in the first 3 months of life show an asymmetry of monocular optokinetic nystagmus (MOKN). The response to temporalwards field motion which they lack is driven in cat by a pathway via binocular cortex: thus the development of this response in human infants might depend on development of binocularity. However, the correlation across individual infants between the age of onset of binocularity and the age at which symmetrical MOKN is attained is relatively weak. It is possible that the neuroanatomical basis of MOKN control differs between cat and human.
Vision screening and photorefraction - the relation of refractive errors to strabismus and amblyopia.
Isotropic photorefraction is a technique well suited for screening infants and young children for refractive errors. The photorefractive measurements have been empirically calibrated against retinoscopic refractions, so errors exceeding selected criteria can be identified in screening and followed up. Such a screening programme is in progress for the population of 6-9 month infants in the City of Cambridge. In 1096 infants screened 5% have been found to have large hypermetropic errors, 1.3% to show a refractive difference between the eyes (anisometropia) and less than 1% to have significant myopia or manifest strabismus. These findings were generally confirmed on retinoscopic examinations. In subsequent follow up of the large hypermetropic errors, most decline with age but a few show little or no change up to age 2 years and some show more change in one eye than the other leading to anisometropia. A trial is underway to examine whether early correction with spectacles can reduce the later incidence of strabismus and amblyopia in hypermetropic infants. Significant astigmatism is found in a large fraction of the infant population; the predominant axis of this astigmatism shows marked and unexplained variations between different locations in England.
Interaction of spatial and temporal integration in global form processing.
The mechanisms by which global structure is extracted from local orientation information are not well understood. Sensitivity to global structure can be investigated using coherence thresholds for detection of global forms of varying complexity, such as parallel and concentric arrays of oriented line elements. In this study, we investigated temporal integration in the detection of these forms and its interaction with spatial integration. We find that for concentric patterns, integration times drop as region size increases from 3 degrees to 10.9 degrees , while for parallel patterns, the reverse is true. The same spatiotemporal relationship was found for Glass patterns as for line element arrays. The two types of organization therefore show quite different spatiotemporal relations, supporting previous arguments that different types of neural mechanism underlie their detection.