Motion-Defined Form Perception in Deprivation Amblyopia.

Purpose: The purpose of this study was to assess motion-defined form perception, including the association with clinical and sensory factors that may drive performance, in each eye of children with deprivation amblyopia due to unilateral cataract. Methods: Coherence thresholds for orientation discrimination of motion-defined form were measured using a staircase procedure in 30 children with deprivation amblyopia and 59 age-matched controls. Visual acuity, stereoacuity, fusion, and interocular suppression were also measured. Fixation stability and fellow-eye global motion thresholds were measured in a subset of children. Results: Motion-defined form coherence thresholds were elevated in 90% of children with deprivation amblyopia when viewing with the amblyopic eye and in 40% when viewing with the fellow eye. The deficit was similar in children with a cataract that had been visually significant at birth (congenital) and in children for whom the cataract appeared later in infancy or childhood (developmental). Poorer motion-defined form perception in amblyopic eyes was associated with poorer visual acuity, poorer binocular function, greater interocular suppression, and the presence of nystagmus. Fellow-eye deficits were not associated with any of these factors, but a temporo-nasal asymmetry for global motion perception in favor of nasalward motion suggested a general disruption in motion perception. Conclusions: Deficits in motion-defined form perception are common in children with deprivation amblyopia and may reflect a problem in motion processing that relies on binocular mechanisms.

White matter but not grey matter predicts change in reading skills after intervention.

This study examined changes in white matter microstructure and grey matter volume, cortical thickness, and cortical surface area before and after reading intervention. Participants included 22 average readers and 13 dyslexic readers (8-9 years old in third grade); the dyslexic readers were enrolled in reading intervention programs at their elementary school. Participants completed scans of diffusion tensor imaging and T1-weighted MRI before and after 3 months of instruction. An a priori region of interest (ROI) analysis was used. Dyslexic readers, compared to average readers, showed higher mean diffusivity in white matter ROIs including bilateral inferior frontal, bilateral insula, left superior temporal, and right supramarginal gyri across time points. Dyslexic readers also had thicker cortex in left fusiform and bilateral supramarginal gyri; whereas, average readers had greater surface area in right fusiform across time. There were no significant changes in white or grey matter following intervention; however, mean diffusivity in the right hemisphere was associated with reading gains over time. White matter organization in the right hemisphere predicts reading changes, and dyslexic readers may have persistent differences in white and grey matter due to ongoing reading deficits.

Impaired Fellow Eye Motion Perception and Abnormal Binocular Function.

Purpose: Binocular discordance due to strabismus, anisometropia, or both may result in not only monocular visual acuity deficits, but also in motion perception deficits. We determined the prevalence of fellow-eye deficits in motion-defined form (MDF) perception, the ability to identify a two-dimensional (2D) shape defined by motion rather than luminance contrast. We also examined the following: the causative role of reduced visual acuity and binocularity, associations with clinical and sensory factors, and effectiveness of binocular amblyopia treatment in alleviating deficits. Methods: Participants included 91 children with residual amblyopia (strabismic, anisometropic, or both; age, 9.0 ± 1.7 years), 79 nonamblyopic children with treated strabismus or anisometropia (age, 8.5 ± 2.1 years), and 20 controls (age, 8.6 ± 1.5 years). MDF coherence thresholds, visual acuity, stereoacuity, and interocular suppression were measured. Results: MDF deficits, relative to controls, were present in the fellow eye of 23% of children with residual amblyopia and 20% of nonamblyopic children. Stereoacuity and age first patched were correlated with MDF threshold (r = 0.29, 95% CI: 0.09-0.47; r = -0.33, 95% CI: -0.13 to -0.50, respectively). MDF deficits were more common in children treated with patching alone than in those receiving contrast-rebalanced binocular treatment with games or movies (t89 = 3.46; P = 0.0008). The latter was associated with a reduction in mean fellow eye MDF threshold (t26 = 6.32, P < 0.0001). Conclusions: Fellow eye MDF deficits are common and likely reflect abnormalities in binocular cortical mechanisms that result from early discordant visual experience. Binocular amblyopia treatment, which is effective in improving amblyopic eye visual acuity, appears to provide a benefit for the fellow eye.

Fellow Eye Deficits in Amblyopia.

Amblyopia is a neurodevelopmental disorder of the visual system, as a result of discordant visual experience during infancy or early childhood. Because amblyopia is typically defined as monocularly reduced visual acuity accompanied by one or more known amblyogenic factors, it is often assumed that the fellow eye is normal and sufficient for tasks like reading and eye-hand coordination. Recent scientific evidence of ocular motor, visual, and visuomotor deficits that are present with fellow eye monocular viewing and with binocular viewing calls this assumption into question. This clinical update reviews the research that has revealed fellow ocular motor and visual deficits and the effect that these deficits have on an amblyopic child's visuomotor and visuocognitive skills. We need to understand how to prevent and rehabilitate the effects of amblyopia not only on the nonpreferred eye but also on the fellow eye.

Longitudinal outcomes of an individualized and intensive reading intervention for third grade students.

Early intervention is known to reduce reading disabilities; however, treatment response is variable, and some students have persistent deficits that require intensive supports. This study examined the immediate and 1-year outcomes of an individualized and intensive reading program for third grade students, which was delivered throughout the school day for an average of 189 hr of instruction over 3 months. These students' performances were compared with two comparison groups, including poor readers who received small group supports and good readers who did not have additional reading instruction. The intensive group showed an improvement in word recognition and decoding fluency immediately after the program and 1 year later, and there was a decrease in significant reading impairments from 62% before intervention to 35% at follow-up. Furthermore, baseline reading, spelling, phonological awareness, and rapid naming skills were predictive of persistent reading deficits at a later time point. Although improvements in reading skills were shown, a significant gap between poor and good readers persisted in the third and fourth grades. This study illustrates the importance of a tertiary intensive reading program, but also the need for continuing supports.

Effect of reading intervention and task difficulty on orthographic and phonological reading systems in the brain.

Children with poor reading skills have differences in brain function when compared to typically-developing readers, and there may also be changes in the brain following reading intervention. However, most functional imaging studies focus on phonological reading tasks with one level of task difficulty. The purpose of this study was to compare good and poor readers on functional magnetic resonance imaging (fMRI) tasks of orthography (spelling) and phonology (rhyming) before and after 3 months of school-based intervention. These tasks were also modulated by task difficulty based on printed word frequency. The results showed that primarily left hemisphere regions were activated for the spelling and rhyming tasks, and poor readers showed a pattern of increased activation in bilateral inferior frontal, bilateral insula, right parietal, and left cerebellum following intervention. Activity in left pars triangularis and right parietal regions were associated with gains in decoding skills. Intervention effects appeared across blocks of easy and difficult words, except for the right parietal cortex. In this region, poor readers had greater activity on the easy word blocks after intervention, which indicates that there was increased recruitment of the right parietal cortex for relatively easy words. These results indicate that effects of intervention may be more evident on phonological tasks in comparison to orthographic tasks, and some of these effects may be modulated by relative task difficulty.

Cortical basis for dichotic pitch perception in developmental dyslexia.

The current study examined auditory processing deficits in dyslexia using a dichotic pitch stimulus and functional MRI. Cortical activation by the dichotic pitch task occurred in bilateral Heschl's gyri, right planum temporale, and right superior temporal sulcus. Adolescents with dyslexia, relative to age-matched controls, illustrated greater activity in left Heschl's gyrus for random noise, less activity in right Heschl's gyrus for all auditory conditions, and less activity in right superior temporal sulcus for a dichotic melody. Subsequent analyses showed that these group differences were attributable to dyslexic readers who performed poorly on the psychophysical task. Furthermore, behavioral performance on phonological reading was correlated to activity from dichotic conditions in right Heschl's gyrus and right superior temporal sulcus. It is postulated that these differences between reader groups is primarily due to a noise exclusion deficit shown previously in dyslexia.

Quantitative measurement of interocular suppression in children with amblyopia.

In this study we explored the possibility of using a dichoptic global motion technique to measure interocular suppression in children with amblyopia. We compared children (5-16 years old) with unilateral anisometropic and/or strabismic amblyopia to age-matched control children. Under dichoptic viewing conditions, contrast interference thresholds were determined with a global motion direction-discrimination task. Using virtual reality goggles, high contrast signal dots were presented to the amblyopic eye, while low contrast noise dots were presented to the non-amblyopic fellow eye. The contrast of the noise dots was increased until discrimination of the motion direction of the signal dots reached chance performance. Contrast interference thresholds were significantly lower in the strabismic group than in the anisometropic and control group. Our results suggest that interocular suppression is stronger in strabismic than in anisometropic amblyopia.

Low- and high-level motion perception deficits in anisometropic and strabismic amblyopia: evidence from fMRI.

Maximum motion displacement (Dmax) is the largest dot displacement in a random-dot kinematogram (RDK) at which direction of motion can be correctly discriminated [Braddick, O. (1974). A short-range process in apparent motion. Vision Research, 14, 519-527]. For first-order RDKs, Dmax gets larger as dot size increases and/or dot density decreases. It has been suggested that this increase in Dmax reflects greater involvement of high-level feature-matching motion mechanisms and less dependence on low-level motion detectors [Sato, T. (1998). Dmax: Relations to low- and high-level motion processes. In T. Watanabe (Ed.), High-level motion processing, computational, neurobiological, and psychophysical perspectives (pp. 115-151). Boston: MIT Press]. Recent psychophysical findings [Ho, C. S., & Giaschi, D. E. (2006). Deficient maximum motion displacement in amblyopia. Vision Research, 46, 4595-4603; Ho, C. S., & Giaschi, D. E. (2007). Stereopsis-dependent deficits in maximum motion displacement. Vision Research, 47, 2778-2785] suggest that this "switch" from low-level to high-level motion processing is also observed in children with anisometropic and strabismic amblyopia as RDK dot size is increased and/or dot density is decreased. However, both high- and low-level Dmax were reduced relative to controls. In this study, we used functional MRI to determine the motion-sensitive areas that may account for the reduced Dmax in amblyopia In the control group, low-level RDKs elicited stronger responses in low-level (posterior occipital) areas and high-level RDKs elicited a greater response in high-level (extra-striate occipital-parietal) areas when activation for high-level RDKs was compared to that for low-level RDKs. Participants with anisometropic amblyopia showed the same pattern of cortical activation although extent of activation differences was less than in controls. For those with strabismic amblyopia, there was almost no difference in the cortical activity for low-level and high-level RDKs, and activation was reduced relative to the other groups. Differences in the extent of cortical activation may be related to amblyogenic subtype.

Low- and high-level first-order random-dot kinematograms: evidence from fMRI.

Maximum motion displacement (Dmax) represents the largest dot displacement in a random-dot kinematogram (RDK) at which direction of motion can be discriminated. Direction discrimination thresholds for maximum motion displacement (Dmax) are not fixed but are stimulus dependent. For first-order RDKs, Dmax is larger as dot size increases and/or dot density decreases. Dmax may be limited by the receptive field size of low-level motion detectors when the dots comprising the RDK are small and densely spaced. With RDKs of increased dot size/decreased dot density, however, Dmax exceeds the spatial limits of these detectors and is likely determined by high-level feature-matching mechanisms. Using functional MRI, we obtained greater activation in posterior occipital areas for low-level RDKs and greater activation in extra-striate occipital and parietal areas for high-level RDKs. This is the first reported neuroimaging evidence supporting proposed low-level and high-level models of motion processing for first-order random-dot stimuli.

Deficient motion-defined and texture-defined figure-ground segregation in amblyopic children.

PURPOSE: Motion-defined form deficits in the fellow eye and the amblyopic eye of children with amblyopia implicate possible direction-selective motion processing or static figure-ground segregation deficits. Deficient motion-defined form perception in the fellow eye of amblyopic children may not be fully accounted for by a general motion processing deficit. This study investigates the contribution of figure-ground segregation deficits to the motion-defined form perception deficits in amblyopia. METHODS: Performances of 6 amblyopic children (5 anisometropic, 1 anisostrabismic) and 32 control children with normal vision were assessed on motion-defined form, texture-defined form, and global motion tasks. RESULTS: Performance on motion-defined and texture-defined form tasks was significantly worse in amblyopic children than in control children. Performance on global motion tasks was not significantly different between the 2 groups. CONCLUSION: Faulty figure-ground segregation mechanisms are likely responsible for the observed motion-defined form perception deficits in amblyopia.

Stereopsis-dependent deficits in maximum motion displacement in strabismic and anisometropic amblyopia.

Direction discrimination thresholds for maximum motion displacement (D(max)) have been previously reported to be abnormal in amblyopic children [Ho, C. S., Giaschi, D. E., Boden, C., Dougherty, R., Cline, R., & Lyons, C. (2005). Deficient motion perception in the fellow eye of amblyopic children. Vision Research, 45, 1615-1627; Ho, C. S., & Giaschi, D. E. (2006). Deficient maximum motion displacement in amblyopia. Vision Research, 46, 4595-4603]. We looked at D(max) thresholds for random dot kinematograms (RDKs) biased toward low- or high-level motion mechanisms. D(max) is thought to be limited, for high-level motion mechanisms, by the efficiency of object feature tracking and probability of false matches. To reduce the influence of low-level mechanisms, we determined thresholds also for a high-pass filtered version of the RDKs. Performance did not significantly differ between strabismic and anisometropic groups with amblyopia, although both groups performed significantly worse than the age-matched control group. D(max) thresholds were higher for children with poor stereoacuity. This was significant in both anisometropic and strabismic groups, and more robust for high-pass filtered RDKs than for unfiltered RDKs. The results imply that impairment of the extra-striate dorsal stream is a likely part of the neural deficit underlying both strabismic and anisometropic amblyopia. This deficit appears to be more dependent on extent of binocularity than etiology. Our findings suggest a possible relationship between fine stereopsis, coarse stereopsis, and motion correspondence mechanisms.

Deficient maximum motion displacement in amblyopia.

Direction discrimination thresholds for maximum motion displacement (Dmax) are not fixed, but are stimulus dependent. Dmax increases with reduced dot probability or increased dot size. We previously reported abnormal Dmax in the fellow eyes of amblyopic children for dense patterns of small dots. To determine how deficits of Dmax in amblyopic eyes compare to those in fellow eyes, thresholds were obtained in both eyes of 9 children with unilateral amblyopia and 9 control children. The expected increase in Dmax was observed for reduced dot probability and increased dot size conditions relative to baseline in both control and amblyopic groups. Both eyes of the amblyopic group demonstrated significant deficits. Our findings implicate abnormal binocular motion processing, which may involve both low-level and high-level motion mechanisms, in the neural deficit underlying amblyopia.

The effects of optical blur on motion and texture perception.

PURPOSE: The purpose of this study is to determine how decreased visual acuity affects performance on tasks of motion and texture perception. METHODS: Positive diopter lenses were used to match three subjects at five levels of decimal visual acuity (DVA) ranging from an uncorrected DVA of 1.6 to the lowest DVA of 0.2. Performance thresholds were determined at each acuity level for five different psychophysical tasks. The tasks assessed the perception of motion-defined form, global motion, maximum motion displacement (Dmax), texture-defined form, and global texture. RESULTS: Reducing visual acuity decreased performance on the tasks of motion-defined form identification, texture-defined form identification, and global texture integration. Performance on the Dmax task improved with a reduction in visual acuity. Performance on the global motion task was unaffected by changes in visual acuity. CONCLUSIONS: Visual acuity should be considered when interpreting the results of developmental or clinical studies of motion and texture perception. The only exception to this is global motion perception, at least when DVA is better than 0.2. The effect of blur on tasks of motion and texture perception may reflect the extent to which high spatial frequency information is required for performance on these tasks.

Sensory and nonsensory influences on children's performance of dichotic pitch perception tasks.

Dichotic pitch perception reflects the auditory system's use of binaural cues to perceptually separate different sound sources and to determine the spatial location of sounds. Several studies were conducted to identify factors that influence children's dichotic pitch perception thresholds. An initial study of school children revealed an age-related improvement in thresholds for lateralizing dichotic pitch tones. In subsequent studies potential sensory and nonsensory limitations on young children's performance of dichotic pitch lateralization tasks were examined. A training study showed that with sufficient practice, young children lateralize dichotic pitch stimuli as well as adults, indicating an age difference in perceptual learning of the lateralization task. Changing the task requirements so that young children made a judgment about the pitch of dichotic pitch tones, rather than the spatial location of the tones, also resulted in significantly better thresholds. These findings indicate that nonsensory factors limit young children's performance of dichotic pitch tasks.

Deficient motion perception in the fellow eye of amblyopic children.

The extent of motion processing deficits and M/dorsal pathway involvement in amblyopia is unclear. Fellow eye performance was assessed in amblyopic children for motion-defined (MD) form, global motion, and maximum displacement (Dmax) tasks. Group performance on MD form was significantly worse in amblyopic children than in control children. Global motion deficits were significantly related to residual binocular function. Abnormally elevated Dmax thresholds were most prevalent in children with anisometropia. Our findings from these three uncorrelated tasks implicate involvement of binocular motion-sensitive mechanisms in the neural deficits of amblyopic children with strabismic, anisometropic, and aniso-strabismic etiologies.

Children with dyslexia: evidence for visual attention deficits in perception of rapid sequences of objects.

The attentional blink (AB) refers to a decrease in accuracy that occurs when observers are required to identify, detect or classify the second of two rapidly-sequential targets. The AB is typically attributed to an inability to rapidly reallocate attentional resources from the first to the second target. Thus, it provides an ideal tool to investigate how visual attention is rapidly allocated to sequences of stimuli such as occurs when reading. In the present work, we compared the magnitude of the AB in children with developmental dyslexia to reading-matched and age-matched control groups. In Experiment 1, when two targets were presented in the same spatial location, the AB deficit was similar in the reading-matched and dyslexic groups, but greater in the dyslexic group than in age-matched controls. In Experiment 2, when targets were presented in different spatial locations, performance in the dyslexic group was worse than the age-matched controls and marginally worse than the reading-matched controls. Taken together, the results argue for developmental delays in the ability of children with dyslexia to allocate attention to rapidly-sequential stimuli, as well as some evidence for difficulties that are unique to this group.

Warning: attending to a mask may be hazardous to your perception.

Object substitution is a type of backward masking that occurs when a mask appears during visual search for a target. We tested the hypothesis that object substitution is an overwriting process triggered by attentional selection of the mask. Impeding attentional selection of a mask by embedding it in an array of distractors eliminated object substitution. Similarly, object substitution did not occur when the mask appeared in advance of the target and, therefore, could not capture attention during search for the target. However, masking was reinstated when the mask was revealed from background contours at the moment of target onset and could therefore capture attention during search. These observations demonstrate that attentional selection of the mask is a necessary step in this type of masking and suggest that object substitution is active overwriting of unattended information triggered by selection of other visual information at a nearby location.

Psychophysical indexes of temporal processing abnormalities in children with developmental dyslexia.

Children with dyslexia and children progressing normally in reading performed several perceptual tasks to determine (a) the psychophysical measures that best differentiate children with dyslexia from children with average reading abilities; (b) the extent of temporal processing deficits in a single, well-defined group of children with dyslexia; and (c) the co-occurrence of visual and auditory temporal processing deficits in children with dyslexia. 4 of our 12 psychophysical tasks indicated differences in temporal processing ability between children with dyslexia and children with good reading skills. These included 2 auditory tasks (dichotic pitch perception and FM tone discrimination) and 2 visual tasks (global motion perception and contrast sensitivity). The battery of 12 tasks successfully classified 80% of the children into their respective reading-level groups. Within the group of children with dyslexia who had temporal processing deficits, most were affected in either audition or vision; few children were affected in both modalities. The observed deficits suggest that impaired temporal processing in dyslexia is most evident on tasks that require the ability to synthesize local, temporally modulated inputs into a global percept and the ability to extract the resultant global percept from a noisy environment.