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Purpose: The dorsal stream vulnerability hypothesis posits that the dorsal stream, responsible for visual motion and visuo-motor processing, may be particularly vulnerable during neurodevelopment. Consistent with this, autism spectrum disorder (ASD) has been associated with deficits in global motion integration, though deficits in ventral stream tasks, such as form identification, have also been reported. In the current study, we examined whether a similar pattern of results is found in a cohort of 381 children born with neurodevelopmental risk factors and exhibiting a wide spectrum of caregiver-reported autistic traits. Methods: We examined the associations between global motion perception, global form perception, fine motor function, visual-motor integration, and autistic traits (autism spectrum quotient, AQ) using linear regression, accounting for possible interactions with sex and other factors relevant to neurodevelopment. Results: All assessments of dorsal stream function were significantly associated with AQ such that worse performance predicted higher AQ scores. We also observed a significant sex interaction, with worse global form perception associated with higher AQ in boys (n = 202) but not girls (n = 179). Conclusion: We found widespread associations between dorsal stream functions and autistic traits. These associations were observed in a large group of children with a range of AQ scores, demonstrating a range of visual function across the full spectrum of autistic traits. In addition, ventral function was associated with AQ in boys but not girls. Sex differences in the associations between visual processing and neurodevelopment should be considered in the designs of future studies. [ABSTRACT FROM AUTHOR]

Introduction: Dextrose gel is widely used as first-line treatment for neonatal hypoglycaemia given its cost-effectiveness and ease of use. The Sugar Babies randomized trial first showed that 40% dextrose gel was more effective in reversing hypoglycaemia than feeding alone. Follow-up of the Sugar Babies Trial cohort at 2 and 4.5 years of age reported that dextrose gel appeared safe, with similar rates of neurosensory impairment in babies randomized to dextrose or placebo gel. However, some effects of neonatal hypoglycaemia may not become apparent until school age. Methods: Follow-up of the Sugar Babies Trial cohort at 9–10 years of age was reported. The primary outcome was low educational achievement in reading or mathematics. Secondary outcomes included other aspects of educational achievement, executive function, visual-motor function, and psychosocial adaptation. Results: Of 227 eligible children, 184 (81%) were assessed at a mean (SD) age of 9.3 (0.2) years. Low educational achievement was similar in dextrose and placebo groups (36/86 [42%] vs. 42/94 [45%]; RR 1.04, 95% CI 0.76, 1.44; p = 0.79). Children allocated to dextrose gel had lower visual perception standard scores (95.2 vs. 100.6; MD −5.68, 95% CI −9.79, −1.57; p = 0.006) and a greater proportion had low (<85) visual perception scores (20/88 [23%] vs. 10/95 [11%]; RR 2.23, 95% CI 1.13, 4.37; p = 0.02). Other secondary outcomes, including other aspects of visual-motor function, were similar in both groups. Conclusion: Treatment dextrose gel does not appear to result in any clinically significant differences in educational achievement or other neurodevelopmental outcomes at mid-childhood. [ABSTRACT FROM AUTHOR]

Rapid visual stimulation can increase synaptic efficacy by repeated synaptic activation. This long‐term potentiation‐like (LTP‐like) effect can induce increased excitability in the human visual cortex. To examine the effect of rapid visual stimulation on perception, we tested the hypothesis that rapid monocular visual stimulation would increase the dominance of the stimulated eye in a binocular rivalry task. Participants (n = 25) viewed orthogonal 0.5 cpd gratings presented in a dichoptic anaglyph to induce binocular rivalry. Rivalry dynamics (alternation rate, dominance, and piecemeal durations) were recorded before and after 2 min of rapid monocular stimulation (9 Hz flicker of one grating) or a binocular control condition (9 Hz alternation of the orthogonal gratings viewed binocularly). Rapid monocular stimulation did not affect alternation rates or piecemeal percept duration. Unexpectedly, the rivalry dominance of the stimulated eye was significantly reduced. A further experiment revealed that this effect could not be explained by monocular adaptation. Together, the results suggest that rapid monocular stimulation boosts dominance in the non‐stimulated eye, possibly by activating homeostatic interocular gain control mechanisms. [ABSTRACT FROM AUTHOR]

A scoping review was undertaken to explore research investigating early interactions and integration of auditory and visual stimuli in the human brain. The focus was on methods used to study low-level multisensory temporal processing using simple stimuli in humans, and how this research has informed our understanding of multisensory perception. The study of multisensory temporal processing probes how the relative timing between signals affects perception. Several tasks, illusions, computational models, and neuroimaging techniques were identified in the literature search. Research into early audiovisual temporal processing in special populations was also reviewed. Recent research has continued to provide support for early integration of crossmodal information. These early interactions can influence higher-level factors, and vice versa. Temporal relationships between auditory and visual stimuli influence multisensory perception, and likely play a substantial role in solving the 'correspondence problem' (how the brain determines which sensory signals belong together, and which should be segregated). [ABSTRACT FROM AUTHOR]

Cortical visual processing involves the ventral stream (form perception) and the dorsal stream (motion perception). We assessed whether mild traumatic brain injury (TBI) differentially affects these two streams. Eleven adults with mild TBI (28 ± 9 yrs, 17 ± 5 months post injury) and 25 controls (25 ± 5 yrs) participated. Participants completed tests of global processing involving Glass patterns (form) and random dot kinematograms (motion), measurement of contrast thresholds for motion direction discrimination, a comprehensive vision screening and the Post-Concussion Symptom Inventory (PCSI). Our results showed that the mild TBI group had significantly higher (worse) global form (mean ± SD: TBI 25 ± 6%, control 21 ± 5%) and motion (TBI 14 ± 7%, control 11 ± 3%) coherence thresholds than controls. The magnitude of the mild TBI group deficit did not differ between the two tasks. Contrast thresholds for motion direction discrimination did not differ between the groups, but were positively correlated with PCSI score (r2 = 0.51. p = 0.01) in the mild TBI group. The mild TBI group had worse outcomes than controls for all clinical measurements of vision except distance visual acuity. In conclusion, mild TBI affects processing in both the dorsal and ventral cortical processing streams equally. In addition, spatiotemporal contrast sensitivity may be related to the symptoms of mild TBI. [ABSTRACT FROM AUTHOR]

Children born very preterm are at a greater risk of abnormal visual and neurological development when compared to children born at full term. Preterm birth is associated with retinopathy of prematurity (a proliferative retinal vascular disease) and can also affect the development of brain structures associated with post-retinal processing of visual information. Visual deficits common in children born preterm, such as reduced visual acuity, strabismus, abnormal stereopsis and refractive error, are likely to be detected through childhood vision screening programs, ophthalmological follow-up or optometric care. However, routine screening may not detect other vision problems, such as reduced visual fields, impaired contrast sensitivity and deficits in cortical visual processing, that may occur in children born preterm. For example, visual functions associated with the dorsal visual processing stream, such as global motion perception and visuomotor integration, may be impaired by preterm birth. These impairments can continue into adolescence and adulthood and may contribute to the difficulties in learning (particularly reading and mathematics), attention, behaviour and cognition that some children born preterm experience. Improvements in understanding the mechanisms by which preterm birth affects vision will inform future screening and interventions for children born preterm. [ABSTRACT FROM AUTHOR]

The dorsal visual processing stream that includes V1, motion sensitive area V5 and the posterior parietal lobe, supports visually guided motor function. Two recent studies have reported associations between global motion perception, a behavioural measure of processing in V5, and motor function in pre-school and school aged children. This indicates a relationship between visual and motor development and also supports the use of global motion perception to assess overall dorsal stream function in studies of human neurodevelopment. We investigated whether associations between vision and motor function were present at 2 years of age, a substantially earlier stage of development. The Bayley III test of Infant and Toddler Development and measures of vision including visual acuity (Cardiff Acuity Cards), stereopsis (Lang stereotest) and global motion perception were attempted in 404 2-year-old children (±4 weeks). Global motion perception (quantified as a motion coherence threshold) was assessed by observing optokinetic nystagmus in response to random dot kinematograms of varying coherence. Linear regression revealed that global motion perception was modestly, but statistically significantly associated with Bayley III composite motor (r 2 = 0.06, P < 0.001, n = 375) and gross motor scores (r 2 = 0.06, p < 0.001, n = 375). The associations remained significant when language score was included in the regression model. In addition, when language score was included in the model, stereopsis was significantly associated with composite motor and fine motor scores, but unaided visual acuity was not statistically significantly associated with any of the motor scores. These results demonstrate that global motion perception and binocular vision are associated with motor function at an early stage of development. Global motion perception can be used as a partial measure of dorsal stream function from early childhood. [ABSTRACT FROM AUTHOR]

The selective serotonin reuptake inhibitor fluoxetine significantly enhances adult visual cortex plasticity within the rat. This effect is related to decreased gamma-aminobutyric acid (GABA) mediated inhibition and identifies fluoxetine as a potential agent for enhancing plasticity in the adult human brain. We tested the hypothesis that fluoxetine would enhance visual perceptual learning of a motion direction discrimination (MDD) task in humans. We also investigated (1) the effect of fluoxetine on visual and motor cortex excitability and (2) the impact of increased GABA mediated inhibition following a single dose of triazolam on post-training MDD task performance. Within a double blind, placebo controlled design, 20 healthy adult participants completed a 19-day course of fluoxetine (n = 10, 20 mg per day) or placebo (n = 10). Participants were trained on the MDD task over the final 5 days of fluoxetine administration. Accuracy for the trained MDD stimulus and an untrained MDD stimulus configuration was assessed before and after training, after triazolam and 1 week after triazolam. Motor and visual cortex excitability were measured using transcranial magnetic stimulation. Fluoxetine did not enhance the magnitude or rate of perceptual learning and full transfer of learning to the untrained stimulus was observed for both groups. After training was complete, trazolam had no effect on trained task performance but significantly impaired untrained task performance. No consistent effects of fluoxetine on cortical excitability were observed. The results do not support the hypothesis that fluoxetine can enhance learning in humans. However, the specific effect of triazolam on MDD task performance for the untrained stimulus suggests that learning and learning transfer rely on dissociable neural mechanisms. [ABSTRACT FROM AUTHOR]

Studies on noninvasive motor cortex stimulation and motor learning demonstrated cortical excitability as a marker for a learning effect. Transcranial direct current stimulation (tDCS) is a non-invasive tool to modulate cortical excitability. It is as yet unknown how tDCS-induced excitability changes and perceptual learning in visual cortex correlate. Our study aimed to examine the influence of tDCS on visual perceptual learning in healthy humans. Additionally, we measured excitability in primary visual cortex (V1). We hypothesized that anodal tDCS would improve and cathodal tDCS would have minor or no effects on visual learning. Anodal, cathodal or sham tDCS were applied over V1 in a randomized, double-blinded design over four consecutive days (n = 30). During 20 min of tDCS, subjects had to learn a visual orientation-discrimination task (ODT). Excitability parameters were measured by analyzing paired-stimulation behavior of visual-evoked potentials (ps-VEP) and by measuring phosphene thresholds (PTs) before and after the stimulation period of 4 days. Compared with sham-tDCS, anodal tDCS led to an improvement of visual discrimination learning (p < 0.003). We found reduced PTs and increased ps-VEP ratios indicating increased cortical excitability after anodal tDCS (PT: p = 0.002, ps-VEP: p = 0.003). Correlation analysis within the anodal tDCS group revealed no significant correlation between PTs and learning effect. For cathodal tDCS, no significant effects on learning or on excitability could be seen. Our results showed that anodal tDCS over V1 resulted in improved visual perceptual learning and increased cortical excitability. tDCS is a promising tool to alter V1 excitability and, hence, perceptual visual learning. [ABSTRACT FROM AUTHOR]

Background Occlusion therapy for amblyopia is predicated on the idea that amblyopia is primarily a disorder of monocular vision; however, there is growing evidence that patients with amblyopia have a structurally intact binocular visual system that is rendered functionally monocular due to suppression. Furthermore, we have found that a dichoptic treatment intervention designed to directly target suppression can result in clinically significant improvement in both binocular and monocular visual function in adult patients with amblyopia. The fact that monocular improvement occurs in the absence of any fellow eye occlusion suggests that amblyopia is, in part, due to chronic suppression. Previously the treatment has been administered as a psychophysical task and more recently as a video game that can be played on video goggles or an i Pod device equipped with a lenticular screen. The aim of this case-series study of 14 amblyopes (six strabismics, six anisometropes and two mixed) ages 13 to 50 years was to investigate: 1. whether the portable video game treatment is suitable for at-home use and 2. whether an anaglyphic version of the i Pod-based video game, which is more convenient for at-home use, has comparable effects to the lenticular version. Methods The dichoptic video game treatment was conducted at home and visual functions assessed before and after treatment. Results We found that at-home use for 10 to 30 hours restored simultaneous binocular perception in 13 of 14 cases along with significant improvements in acuity (0.11 ± 0.08 logMAR) and stereopsis (0.6 ± 0.5 log units). Furthermore, the anaglyph and lenticular platforms were equally effective. In addition, the i Pod devices were able to record a complete and accurate picture of treatment compliance. Conclusion The home-based dichoptic i Pod approach represents a viable treatment for adults with amblyopia. [ABSTRACT FROM AUTHOR]

Abstract: This study examined the effects of visual cortex transcranial direct current stimulation (tDCS) on visual processing and learning. Participants performed a contrast detection task on two consecutive days. Each session consisted of a baseline measurement followed by measurements made during active or sham stimulation. On the first day, one group received anodal stimulation to primary visual cortex (V1), while another received cathodal stimulation. Stimulation polarity was reversed for these groups on the second day. The third (control) group of subjects received sham stimulation on both days. No improvements or decrements in contrast sensitivity relative to the same-day baseline were observed during real tDCS, nor was any within-session learning trend observed. However, task performance improved significantly from Day 1 to Day 2 for the participants who received cathodal tDCS on Day 1 and for the sham group. No such improvement was found for the participants who received anodal stimulation on Day 1, indicating that anodal tDCS blocked overnight consolidation of visual learning, perhaps through engagement of inhibitory homeostatic plasticity mechanisms or alteration of the signal-to-noise ratio within stimulated cortex. These results show that applying tDCS to the visual cortex can modify consolidation of visual learning. [Copyright &y& Elsevier]

Abstract: Amblyopia is characterised by visual deficits in both spatial vision and motion perception. While the spatial deficits are thought to result from deficient processing at both low and higher level stages of visual processing, the deficits in motion perception appear to result primarily from deficits involving higher level processing. Specifically, it has been argued that the motion deficit in amblyopia occurs when local motion information is pooled spatially and that this process is abnormally susceptible to the presence of noise elements in the stimulus. Here we investigated motion direction discrimination for abruptly presented two-frame Gabor stimuli in a group of five strabismic amblyopes and five control observers. Motion direction discrimination for this stimulus is inherently noisy and relies on the signal/noise processing of motion detectors. We varied viewing condition (monocular vs. binocular), stimulus size (5.3–18.5°) and stimulus contrast (high vs. low) in order to assess the effects of binocular summation, spatial summation and contrast on task performance. No differences were found for the high contrast stimuli; however the low contrast stimuli revealed differences between the control and amblyopic groups and between fellow fixing and amblyopic eyes. Control participants exhibited pronounced binocular summation for this task (on average a factor of 3.7), whereas amblyopes showed no such effect. In addition, the spatial summation that occurred for control eyes and the fellow eye of amblyopes was significantly attenuated for the amblyopic eyes relative to fellow eyes. Our results support the hypothesis that pooling of local motion information from amblyopic eyes is abnormal and highly sensitive to noise. [Copyright &y& Elsevier]

Abstract: Much of the debate surrounding the precise functional role of brain mechanisms implicated in the processing of human faces can be explained when considering that studies into early-stage neural representations of the spatial arrangement of facial features are potentially contaminated by “higher-level” cognitive attributes associated with human faces. One way to bypass such attributes would be to employ ambiguous stimuli that are not biased toward any particular object class and analyze neural activity in response to those stimuli in a manner similar to traditional reverse correlation for mapping visual receptive fields. Accordingly, we sought to derive whole face representations directly from neural activity in the human brain using electroencephalography (EEG). We presented ambiguous fractal noise stimuli to human participants and asked them to rate each stimulus along a “face not present” to “face present” continuum while simultaneously recording EEGs. All EEGs were subjected to a time–frequency analysis near 170 ms (negative amplitudes near 170 ms post-stimulus onset have been linked to early face processing) for five different frequency bands (delta, theta, alpha, beta, and gamma) on a trial-by-trial basis, independent of the behavioral responses. Images containing apparent face-like structure were obtained for theta through gamma frequency bands for strong negative amplitudes near 170 ms post-stimulus onset. The presence of the face-like structure in the spatial images derived from brain signals was objectively verified using both Fourier methods and trained neural networks. The results support the use of a modified reverse correlation technique with EEG as a non-biased assessment of brain processes involved in the complex integration of spatial information into objects such as human faces. [Copyright &y& Elsevier]

Global motion perception is often used as an index of dorsal visual stream function in neurodevelopmental studies. However, the relationship between global motion perception and visuomotor control, a primary function of the dorsal stream, is unclear. We measured global motion perception (motion coherence threshold; MCT) and performance on standardized measures of motor function in 606 4.5-year-old children born at risk of abnormal neurodevelopment. Visual acuity, stereoacuity and verbal IQ were also assessed. After adjustment for verbal IQ or both visual acuity and stereoacuity, MCT was modestly, but significantly, associated with all components of motor function with the exception of fine motor scores. In a separate analysis, stereoacuity, but not visual acuity, was significantly associated with both gross and fine motor scores. These results indicate that the development of motion perception and stereoacuity are associated with motor function in pre-school children. [ABSTRACT FROM AUTHOR]

Global motion processing depends on a network of brain regions that includes extrastriate area V5 in the dorsal visual stream. For this reason, psychophysical measures of global motion perception have been used to provide a behavioral measure of dorsal stream function. This approach assumes that global motion is relatively independent of visual functions that arise earlier in the visual processing hierarchy such as contrast sensitivity and visual acuity. We tested this assumption by assessing the relationships between global motion perception, contrast sensitivity for coherent motion direction discrimination (henceforth referred to as contrast sensitivity) and habitual visual acuity in a large group of 4.5-year-old children (n=117). The children were born at risk of abnormal neurodevelopment because of prenatal drug exposure or risk factors for neonatal hypoglycemia. Motion coherence thresholds, a measure of global motion perception, were assessed using random dot kinematograms. The contrast of the stimuli was fixed at 100% and coherence was varied. Contrast sensitivity was measured using the same stimuli by fixing motion coherence at 100% and varying dot contrast. Stereoacuity was also measured. Motion coherence thresholds were not correlated with contrast sensitivity or visual acuity. However, lower (better) motion coherence thresholds were correlated with finer stereoacuity (ρ=0.38, p=0.004). Contrast sensitivity and visual acuity were also correlated (ρ=-0.26, p=0.004) with each other. These results indicate that global motion perception for high contrast stimuli is independent of contrast sensitivity and visual acuity and can be used to assess motion integration mechanisms in children. [ABSTRACT FROM AUTHOR]

Optokinetic nystagmus (OKN) is the sawtooth movement of the eye elicited when an observer views a repeated moving pattern. We present a method for identifying the presence and direction of OKN in recordings of the eye made using a standard off-the-shelf video-camera or webcam. Our approach uses vertical edge detection to determine the limbus/iris boundary, and we estimate the velocity of the edge using Lucas–Kanade optical flow. Heuristic rules are applied to identify saccadic velocity peaks from the resulting velocity signal. The normalized average of the resulting peaks is used to estimate the presence/direction of OKN. Our preliminary testing with six participants observing global motion stimuli with full or partial coherence yields an accuracy of 93% which compares favorably to the performance of an experienced human observer (98% accuracy). Additional tests using high contrast, square-wave gratings show that performance of the technique is consistent at stimulus speeds of 5 and 10 deg/s and that OKN is not reported by the algorithm when participants view stationary stimuli. [ABSTRACT FROM AUTHOR]