Neural Correlates of Speed-Tuned Motion Perception in Healthy Adults

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.

Alterations in white matter integrity and network topological properties are associated with a decrease in global motion perception in older adults

Previous studies have mainly explored the effects of structural and functional aging of cortical regions on global motion sensitivity in older adults, but none have explored the structural white matter (WM) substrates underlying the age-related decrease in global motion perception (GMP). In this study, random dot kinematogram and diffusion tensor imaging were used to investigate the effects of age-related reductions in WM fiber integrity and connectivity across various regions on GMP. We recruited 106 younger adults and 94 older adults and utilized both tract-based spatial statistics analysis and graph theoretical analysis to comprehensively investigate group differences in WM microstructural and network connections between older and younger adults at the microscopic and macroscopic levels. Moreover, partial correlation analysis was used to explore the relationship between alterations in WM and the age-related decrease in GMP. The results showed that decreased GMP in older adults was related to decreased fractional anisotropy (FA) of the inferior frontal-occipital fasciculus, inferior longitudinal fasciculus, anterior thalamic radiation, superior longitudinal fasciculus, and cingulum cingulate gyrus. Decreased global efficiency of the WM structural network and increased characteristic path length were closely associated with decreased global motion sensitivity. These results suggest that the reduced GMP in older adults may stem from reduced WM integrity in specific regions of WM fiber tracts as well as decreased efficiency of information integration and communication between distant cortical regions, supporting the “disconnection hypothesis” of cognitive aging.

The structural basis of age-related decline in global motion perception at fast and slow speeds

A decrease in global motion perception (GMP) has been reported in older adults, and this age-related decline in GMP varies with the speed of global motion. However, no studies have investigated whether the asynchronous age-related decline in GMP is related to degenerative changes in brain structure. In this study, the random dot kinematogram paradigm and structural magnetic resonance imaging were used to investigate the asynchronous aging of GMP at fast and slow speeds (called fast GMP and slow GMP, respectively) and their relationships with brain structure. Ninety-four older adults (65.74 ± 4.50 yrs) and 90 younger adults (22.83 ± 4.84 yrs) participated in the experiment. The results showed that older adults had higher motion coherence thresholds (MCT) than younger adults at both fast and slow speeds. Brain-behavior correlation analyses of younger adults revealed that none of the correlations between morphological measures and MCTs survived correction for multiple comparisons. For older adults, slow MCT was correlated with cortical thickness in the bilateral V4v, V5/MT+, left V7, V8, LO, and surface area in the right V7. Fast MCT was significantly correlated with gray matter volume in the right V7 and thickness in the left V5/MT+. These results support the view that global motion extraction occurs within two speed-tuned systems that are at least partially independent in terms of their neural substrates, which deteriorate with age at different speeds. Aging of GMP is also associated with morphological changes in the visual cortex. Age-related cerebral atrophy in the dorsal stream may impair both fast and slow GMP, whereas aging of the ventral stream specifically impairs slow GMP.

Systems-level decoding reveals the cognitive and behavioral profile of the human intraparietal sulcus

INTRODUCTION

The human intraparietal sulcus (IPS) covers large portions of the posterior cortical surface and has been implicated in a variety of cognitive functions. It is, however, unclear how cognitive functions dissociate between the IPS's heterogeneous subdivisions, particularly in perspective to their connectivity profile.

METHODS

We applied a neuroinformatics driven system-level decoding on three cytoarchitectural distinct subdivisions (hIP1, hIP2, hIP3) per hemisphere, with the aim to disentangle the cognitive profile of the IPS in conjunction with functionally connected cortical regions.

RESULTS

The system-level decoding revealed nine functional systems based on meta-analytical associations of IPS subdivisions and their cortical coactivations: Two systems-working memory and numeric cognition-which are centered on all IPS subdivisions, and seven systems-attention, language, grasping, recognition memory, rotation, detection of motions/shapes and navigation-with varying degrees of dissociation across subdivisions and hemispheres. By probing the spatial overlap between systems-level co-activations of the IPS and seven canonical intrinsic resting state networks, we observed a trend toward more co-activation between hIP1 and the front parietal network, between hIP2 and hIP3 and the dorsal attention network, and between hIP3 and the visual and somatomotor network.

DISCUSSION

Our results confirm previous findings on the IPS's role in cognition but also point to previously unknown differentiation along the IPS, which present viable starting points for future work. We also present the systems-level decoding as promising approach toward functional decoding of the human connectome.

Olfactory Stimulation Modulates Visual Perception Without Training

Considerable research shows that olfactory stimulations affect other modalities in high-level cognitive functions such as emotion. However, little known fact is that olfaction modulates low-level perception of other sensory modalities. Although some studies showed that olfaction had influenced on the other low-level perception, all of them required specific experiences like perceptual training. To test the possibility that olfaction modulates low-level perception without training, we conducted a series of psychophysical and neuroimaging experiments. From the results of a visual task in which participants reported the speed of moving dots, we found that participants perceived the slower motions with a lemon smell and the faster motions with a vanilla smell, without any specific training. In functional magnetic resonance imaging (fMRI) studies, brain activities in the visual cortices [V1 and human middle temporal area (hMT)] changed based on the type of olfactory stimulation. Our findings provide us with the first direct evidence that olfaction modulates low-level visual perception without training, thereby indicating that olfactory-visual effect is not an acquired behavior but an innate behavior. The present results show us with a new crossmodal effect between olfaction and vision, and bring a unique opportunity to reconsider some fundamental roles of olfactory function.

Effect of Visual Field Location on Global Motion Perception: A Developmental Study

Previous work has shown that motion perception in school-age children is similar to that of adults for fast speeds but is immature at slow speeds for stimuli presented in the central visual field. This study examined whether visual field location affects this developmental pattern. We measured left/right and up/down global motion direction discrimination for fast and slow speeds in 7- to 10-year-old children and in adults with stimuli presented to upper, central, or lower visual fields. For left/right direction discrimination, children showed significantly higher (worse) coherence thresholds than adults for slow, but not fast, speeds in the central visual field. In the upper and lower visual fields, children showed significantly higher coherence thresholds than adults for both speeds. For up/down direction discrimination, children showed similar performance to adults for the central visual field. In the upper and lower visual fields, children performed significantly worse than adults; this finding was speed-tuned only for the lower visual field. Thus, children show immature global motion perception in the periphery even when performance in central vision is adult-like. These results enrich our understanding of motion perception development in children with typical vision.

Concurrent maturation of visuomotor skills and motion perception in typically-developing children and adolescents

Perceptual and visuomotor skills undergo considerable development from early childhood into adolescence; however, the concurrent maturation of these skills has not yet been examined. This study assessed visuomotor function and motion perception in a cross-section of 226 typically-developing children between 4 and 16 years of age. Participants were tested on three tasks hypothesized to engage the dorsal visual stream: threading a bead on a needle, marking dots using a pen, and discriminating form defined by motion contrast. Mature performance was reached between 8 and 12 years, with youngest maturation for kinematic measures for a reach-to-grasp task, and oldest maturation for a precision tapping task. Performance on the motion perception task shared no association with motor skills after controlling for age.

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.