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IntroductionThis study examines a set of oculomotor measurements, or “oculometric” biomarkers, as potential early indicators of visual and visuomotor deficits due to retinal toxicity in asymptomatic Systemic Lupus Erythematosus (SLE) patients on long-term hydroxychloroquine (HCQ) treatment. The aim is to identify subclinical functional impairments that are otherwise undetectable by standard clinical tests and to link them to structural retinal changes.MethodsWe measured oculomotor responses in a cohort of SLE patients on chronic HCQ therapy using a previously established behavioral task and analysis technique. We also examined the relationship between oculometrics, OCT measures of retinal thickness, and standard clinical perimetry measures of visual function in our patient group using Bivariate Pearson Correlation and a Linear Mixed-Effects Model (LMM).ResultsSignificant visual and visuomotor deficits were found in 12 asymptomatic SLE patients on long-term HCQ therapy compared to a cohort of 17 age-matched healthy controls. Notably, six oculometrics were significantly different. The median initial pursuit acceleration was 22%, steady-state pursuit gain 16%, proportion smooth 7%, and target speed responsiveness 31% lower, while catch-up saccade amplitude was 46% and fixation error 46% larger. Excluding the two patients with diagnosed mild toxicity, four oculometrics, all but fixation error and proportion smooth, remained significantly impaired compared to controls. Across our population of 12 patients (24 retinae), we found that pursuit latency, initial acceleration, steady-state gain, and fixation error were linearly related to retinal thickness even when age was accounted for, while standard measures of clinical function (Mean Deviation and Pattern Standard Deviation) were not.DiscussionOur data show that specific oculometrics are sensitive early biomarkers of functional deficits in SLE patients on HCQ that could be harnessed to assist in the early detection of HCQ-induced retinal toxicity and other visual pathologies, potentially providing early diagnostic value beyond standard visual field and OCT evaluations.

Introduction: Autism spectrum disorder (ASD) is a neurodevelopmental disorder, which is reportedly related to difficulties in the visual processing of human motion, such as biologicalmotion and gestures. Moreover, neurotypical (here, we mention it as individuals without a diagnosis) adults with autistic traits are clumsier than those without autistic traits when passing by others. It is still unclear whether the clumsiness derived from atypical visual processing of another's approaching gait motion. We aim to address this question by investigating the association between autistic traits in neurotypical adults and the visual processing of an approaching life-sized avatar's gait. Methods: We clarified a typical visual motion processing and autistic traits in daily life in 26 neurotypical adults by analyzing the subthreshold autism trait questionnaire (SATQ) score, a 24-item self-report scale of ASD, and event-related potentials (ERPs) in response to walking motion of a passing avatar. Videos of walking life-sized virtual avatars approaching and retreating were presented as visual stimuli. Results and discussion: The association between the participants' SATQ scores and the latencies and amplitudes of the ERPs was examined. ERP components (N170 and P200) components were identified at T5 and T6 electrodes. Participants reporting higher SATQ scores had longer latencies of P200 at T6 and lower amplitudes of P200 at T5 and T6 electrodes for the approaching avatar than those reporting lower SATQ scores. These findings indicate that adults with autistic traits have delayed and less sensitive visual processing of the approaching avatar. It suggests that while passing another person, these individuals have atypical visual processing of their approach. This study may contribute to elucidating autistic traits from the perspective of visual processing in an environment simulating daily life. [ABSTRACT FROM AUTHOR]

Introduction: Ocular tracking of a moving object requires tight coordination between smooth pursuit and saccadic eye movements. Normally, pursuit drives gaze velocity to closely match target velocity, with residual position offsets corrected by catch-up saccades. However, how/if common stressors affect this coordination is largely unknown. This study seeks to elucidate the effects of acute and chronic sleep loss, and low-dose alcohol, on saccade-pursuit coordination, as well as that of caffeine. Methods: We used an ocular tracking paradigm to assess three metrics of tracking (pursuit gain, saccade rate, saccade amplitude) and to compute "ground lost" (from reductions in steady-state pursuit gain) and "ground recouped" (from increases in steady-state saccade rate and/or amplitude). We emphasize that these are measures of relative changes in positional offsets, and not absolute offset from the fovea. Results: Under low-dose alcohol and acute sleep loss, ground lost was similarly large. However, under the former, it was nearly completely recouped by saccades, whereas under the latter, compensation was at best partial. Under chronic sleep restriction and acute sleep loss with a caffeine countermeasure, the pursuit deficit was dramatically smaller, yet saccadic behavior remained altered from baseline. In particular, saccadic rate remained significantly elevated, despite the fact that ground lost was minimal. Discussion: This constellation of findings demonstrates differential impacts on saccade-pursuit coordination with low-dose alcohol impacting only pursuit, likely through extrastriate cortical pathways, while acute sleep loss not only disrupts pursuit but also undermines saccadic compensation, likely through midbrain/brainstem pathways. Furthermore, while chronic sleep loss and caffeine-mitigated acute sleep loss show little residual pursuit deficit, consistent with uncompromised cortical visual processing, they nonetheless show an elevated saccade rate, suggesting residual midbrain and/or brainstem impacts. [ABSTRACT FROM AUTHOR]

IntroductionOcular tracking of a moving object requires tight coordination between smooth pursuit and saccadic eye movements. Normally, pursuit drives gaze velocity to closely match target velocity, with residual position offsets corrected by catch-up saccades. However, how/if common stressors affect this coordination is largely unknown. This study seeks to elucidate the effects of acute and chronic sleep loss, and low-dose alcohol, on saccade-pursuit coordination, as well as that of caffeine.MethodsWe used an ocular tracking paradigm to assess three metrics of tracking (pursuit gain, saccade rate, saccade amplitude) and to compute “ground lost” (from reductions in steady-state pursuit gain) and “ground recouped” (from increases in steady-state saccade rate and/or amplitude). We emphasize that these are measures of relative changes in positional offsets, and not absolute offset from the fovea.ResultsUnder low-dose alcohol and acute sleep loss, ground lost was similarly large. However, under the former, it was nearly completely recouped by saccades, whereas under the latter, compensation was at best partial. Under chronic sleep restriction and acute sleep loss with a caffeine countermeasure, the pursuit deficit was dramatically smaller, yet saccadic behavior remained altered from baseline. In particular, saccadic rate remained significantly elevated, despite the fact that ground lost was minimal.DiscussionThis constellation of findings demonstrates differential impacts on saccade-pursuit coordination with low-dose alcohol impacting only pursuit, likely through extrastriate cortical pathways, while acute sleep loss not only disrupts pursuit but also undermines saccadic compensation, likely through midbrain/brainstem pathways. Furthermore, while chronic sleep loss and caffeine-mitigated acute sleep loss show little residual pursuit deficit, consistent with uncompromised cortical visual processing, they nonetheless show an elevated saccade rate, suggesting residual midbrain and/or brainstem impacts.

The nervous system is under tight energy constraints and must represent information efficiently. This is particularly relevant in the dorsal part of the medial superior temporal area (MSTd) in primates where neurons encode complex motion patterns to support a variety of behaviors. A sparse decomposition model based on a dimensionality reduction principle known as nonnegative matrix factorization (NMF) was previously shown to account for a wide range of monkey MSTd visual response properties. This model resulted in sparse, parts-based representations that could be regarded as basis flow fields, a linear superposition of which accurately reconstructed the input stimuli. This model provided evidence that the seemingly complex response properties of MSTd may be a by-product of MSTd neurons performing dimensionality reduction on their input. However, an open question is how a neural circuit could carry out this function. In the current study, we propose a spiking neural network (SNN) model of MSTd based on evolved spike-timing-dependent plasticity and homeostatic synaptic scaling (STDP-H) learning rules. We demonstrate that the SNN model learns compressed and efficient representations of the input patterns similar to the patterns that emerge from NMF, resulting in MSTd-like receptive fields observed in monkeys. This SNN model suggests that STDP-H observed in the nervous system may be performing a similar function as NMF with sparsity constraints, which provides a test bed for mechanistic theories of how MSTd may efficiently encode complex patterns of visual motion to support robust self-motion perception. [ABSTRACT FROM AUTHOR]

Key points: Oculomotor behaviours are commonly used to evaluate sensorimotor disruption due to ethanol (EtOH).The current study demonstrates the dose‐dependent impairment in oculomotor and ocular behaviours across a range of ultra‐low BACs (<0.035%).Processing of target speed and direction, as well as pursuit eye movements, are significantly impaired at 0.015% BAC, suggesting impaired neural activity within brain regions associated with the visual processing of motion.Catch‐up saccades during steady visual tracking of the moving target compensate for the reduced vigour of smooth eye movements that occurs with the ingestion of low‐dose alcohol.Saccade dynamics start to become 'sluggish' at as low as 0.035% BAC.Pupillary light responses appear unaffected at BAC levels up to 0.065%. Changes in oculomotor behaviours are often used as metrics of sensorimotor disruption due to ethanol (EtOH); however, previous studies have focused on deficits at blood‐alcohol concentrations (BACs) above about 0.04%. We investigated the dose dependence of the impairment in oculomotor and ocular behaviours caused by EtOH administration across a range of ultra‐low BACs (≤0.035%). We took repeated measures of oculomotor and ocular performance from sixteen participants, both pre‐ and post‐EtOH administration. To assess the neurological impacts across a wide range of brain areas and pathways, our protocol measured 21 largely independent performance metrics extracted from a range of behavioural responses ranging from ocular tracking of radial step‐ramp stimuli, to eccentric gaze holding, to pupillary responses evoked by light flashes. Our results show significant impairment of pursuit and visual motion processing at 0.015% BAC, reflecting degraded neural processing within extrastriate cortical pathways. However, catch‐up saccades largely compensate for the tracking displacement shortfall caused by low pursuit gain, although there still is significant residual retinal slip and thus degraded dynamic acuity. Furthermore, although saccades are more frequent, their dynamics are more sluggish (i.e. show lower peak velocities) starting at BAC levels as low as 0.035%. Small effects in eccentric gaze holding and no effect in pupillary response dynamics were observed at levels below 0.07%, showing the higher sensitivity of the pursuit response to very low levels of blood alcohol, under the conditions of our study. Key points: Oculomotor behaviours are commonly used to evaluate sensorimotor disruption due to ethanol (EtOH).The current study demonstrates the dose‐dependent impairment in oculomotor and ocular behaviours across a range of ultra‐low BACs (<0.035%).Processing of target speed and direction, as well as pursuit eye movements, are significantly impaired at 0.015% BAC, suggesting impaired neural activity within brain regions associated with the visual processing of motion.Catch‐up saccades during steady visual tracking of the moving target compensate for the reduced vigour of smooth eye movements that occurs with the ingestion of low‐dose alcohol.Saccade dynamics start to become 'sluggish' at as low as 0.035% BAC.Pupillary light responses appear unaffected at BAC levels up to 0.065%. [ABSTRACT FROM AUTHOR]

In birds, optic flow is processed by a retinal‐recipient nucleus in the pretectum, the nucleus lentiformis mesencephali (LM), which then projects to the cerebellum, a key site for sensorimotor integration. Previous studies have shown that the LM is hypertrophied in hummingbirds, and that LM cell response properties differ between hummingbirds and other birds. Given these differences in anatomy and physiology, we ask here if there are also species differences in the connectivity of the LM. The LM is separated into lateral and medial subdivisions, which project to the oculomotor cerebellum and the vestibulocerebellum. In pigeons, the projection to the vestibulocerebellum largely arises from the lateral LM; the projection to the oculomotor cerebellum largely arises from the medial LM. Here, using retrograde tracing, we demonstrate differences in the distribution of projections in these pathways between Anna's hummingbirds (Calypte anna), zebra finches (Taeniopygia guttata), and pigeons (Columba livia). In all three species, the projections to the vestibulocerebellum were largely from lateral LM. In contrast, projections to the oculomotor cerebellum in hummingbirds and zebra finches do not originate in the medial LM (as in pigeons) but instead largely arise from pretectal structures just medial, the nucleus laminaris precommissuralis and nucleus principalis precommissuralis. These species differences in projection patterns provide further evidence that optic flow circuits differ among bird species with distinct modes of flight. [ABSTRACT FROM AUTHOR]

The present study tested whether or not functional adaptations following congenital blindness are maintained in humans after sight-restoration and whether they interfere with visual recovery. In permanently congenital blind individuals both intramodal plasticity (e.g. changes in auditory cortex) as well as crossmodal plasticity (e.g. an activation of visual cortex by auditory stimuli) have been observed. Both phenomena were hypothesized to contribute to improved auditory functions. For example, it has been shown that early permanently blind individuals outperform sighted controls in auditory motion processing and that auditory motion stimuli elicit activity in typical visual motion areas. Yet it is unknown what happens to these behavioral adaptations and cortical reorganizations when sight is restored, that is, whether compensatory auditory changes are lost and to which degree visual motion processing is reinstalled. Here we employed a combined behavioral-electrophysiological approach in a group of sight-recovery individuals with a history of a transient phase of congenital blindness lasting for several months to several years. They, as well as two control groups, one with visual impairments, one normally sighted, were tested in a visual and an auditory motion discrimination experiment. Task difficulty was manipulated by varying the visual motion coherence and the signal to noise ratio, respectively. The congenital cataract-reversal individuals showed lower performance in the visual global motion task than both control groups. At the same time, they outperformed both control groups in auditory motion processing suggesting that at least some compensatory behavioral adaptation as a consequence of a complete blindness from birth was maintained. Alpha oscillatory activity during the visual task was significantly lower in congenital cataract reversal individuals and they did not show ERPs modulated by visual motion coherence as observed in both control groups. In contrast, beta oscillatory activity in the auditory task, which varied as a function of SNR in all groups, was overall enhanced in congenital cataract reversal individuals. These results suggest that intramodal plasticity elicited by a transient phase of blindness was maintained and might mediate the prevailing auditory processing advantages in congenital cataract reversal individuals. By contrast, auditory and visual motion processing do not seem to compete for the same neural resources. We speculate that incomplete visual recovery is due to impaired neural network turning which seems to depend on early visual input. The present results demonstrate a privilege of the first arriving input for shaping neural circuits mediating both auditory and visual functions. [ABSTRACT FROM AUTHOR]

Interaction with the environment often involves situations requiring visuomotor integration. For instance, in fast interceptive actions, the brain must integrate visual information of motion with the appropriate motor action. In such dynamic situation, the brain may control movement based on predictions of where the object will be in the future and when it will arrive there. Although previous studies have analyzed brain regions associated with processing visual information of motion, motor control and visuomotor integration with static objects, less is known about visuomotor integration with moving objects. In the present study we used an event-related fMRI experiment to investigate brain areas integrating visual information of motion with motor action in response to moving objects. Twenty healthy volunteers performed an interceptive task where they had to press a button in synchrony with the arrival of a horizontally moving target at a predefined location. They also performed two control tasks—simple reaction and attention to visual motion—in order to identify and exclude brain areas that would be involved in motor or visual motion processing components that are inherent to interceptive tasks. Through a conjunction analysis, we show greater BOLD signal in a bilateral dorsal fronto-parietal network, as well as the intraparietal sulcus, angular gyrus, and human visual motion area hV5+. We discuss these results with respect to their previously identified functions, and suggest they play a role in visuomotor integration with moving objects. [ABSTRACT FROM AUTHOR]

Motion perception is a pervasive nature of vision and is affected by both immediate pattern of sensory inputs and prior experiences acquired through associations. Recently, several studies reported that an association can be established quickly between directions of visual motion and static sounds of distinct frequencies. After the association is formed, sounds are able to change the perceived direction of visual motion. To determine whether such rapidly acquired audiovisual associations and their subsequent influences on visual motion perception are dependent on the involvement of higher-order attentive tracking mechanisms, we designed psychophysical experiments using regular and reverse-phi random dot motions isolating low-level pre-attentive motion processing. Our results show that an association between the directions of low-level visual motion and static sounds can be formed and this audiovisual association alters the subsequent perception of low-level visual motion. These findings support the view that audiovisual associations are not restricted to high-level attention based motion system and early-level visual motion processing has some potential role.

The perception of visual motion can be profoundly influenced by visual context. To gain insight into how the visual system represents motion speed, we investigated how a background stimulus that did not move in a net direction influenced the perceived speed of a center stimulus. Visual stimuli were two overlapping random-dot patterns. The center stimulus moved coherently in a fixed direction, whereas the background stimulus moved randomly. We found that human subjects perceived the speed of the center stimulus to be significantly faster than its veridical speed when the background contained motion noise. Interestingly, the perceived speed was tuned to the noise level of the background. When the speed of the center stimulus was low, the highest perceived speed was reached when the background had a low level of motion noise. As the center speed increased, the peak perceived speed was reached at a progressively higher background noise level. The effect of speed overestimation required the center stimulus to overlap with the background. Increasing the background size within a certain range enhanced the effect, suggesting spatial integration. The speed overestimation was significantly reduced or abolished when the center stimulus and the background stimulus had different colors, or when they were placed at different depths. When the center- and background-stimuli were perceptually separable, speed overestimation was correlated with perceptual similarity between the center- and backgroundstimuli. These results suggest that integration of motion energy from random motion noise has a significant impact on speed perception. Our findings put new constraints on models regarding the neural basis of speed perception. [ABSTRACT FROM AUTHOR]

Neurons in the dorsal subregion of the medial superior temporal (MSTd) area of the macaque respond to large, complex patterns of retinal flow, implying a role in the analysis of self-motion. Some neurons are selective for the expanding radial motion that occurs as an observer moves through the environment ("heading"), and computational models can account for this finding. However, ample evidence suggests that MSTd neurons exhibit a continuum ofvisual response selectivity to large-field motion stimuli. Furthermore, the underlying computational principles by which these response properties are derived remain poorly understood. Here we describe a computational model of macaque MSTd based on the hypothesis that neurons in MSTd efficiently encode the continuum of large-field retinal flow patterns on the basis of inputs received from neurons in MT with receptive fields that resemble basis vectors recovered with non-negative matrix factorization. These assumptions are sufficient to quantitatively simulate neurophysiological response properties of MSTd cells, such as 3D translation and rotation selectivity, suggesting that these properties might simply be a byproduct of MSTd neurons performing dimensionality reduction on their inputs. At the population level, model MSTd accurately predicts eye velocity and heading using a sparse distributed code, consistent with the idea that biological MSTd might be well equipped to efficiently encode various self-motion variables. The present work aims to add some structure to the often contradictory findings about macaque MSTd, and offers a biologically plausible account of a wide range of visual response properties ranging from single-unit selectivity to population statistics. [ABSTRACT FROM AUTHOR]

Neurons in area MT/V5 of the macaque visual cortex encode visual motion. Some cells are selective for the motion of oriented features (component direction-selective, CDS); others respond to the true direction of complex patterns (pattern-direction selective, PDS). There is a continuum of selectivity in MT, with CDS cells at one extreme and PDS cells at the other; we compute a pattern index that captures this variation. It is unknown how a neuron's pattern index is related to its other tuning characteristics. We therefore analyzed the responses of 792 MT cells recorded in the course of other experiments from opiate-anesthetized macaque monkeys, as a function of the direction, spatial frequency, drift rate, size, and contrast of sinusoidal gratings and of the direction and speed of random-dot textures. We also compared MT responses to those of 718 V1 cells. As expected, MT cells with higher pattern index tended to have stronger direction selectivity and broader direction tuning to gratings, and they responded better to plaids than to gratings. Strongly PDS cells also tended to have smaller receptive fields and stronger surround suppression. Interestingly, they also responded preferentially to higher drift rates and higher speeds of moving dots. The spatial frequency preferences of PDS cells depended strongly on their preferred temporal frequencies, whereas these preferences were independent in component-selective cells. Pattern direction selectivity is statistically associated with many response properties of MT cells but not strongly associated with any particular property. Pattern-selective signals are thus available in association with most other signals exported by MT. [ABSTRACT FROM AUTHOR]

Many neurons in visual cortical area MT signal the direction of motion of complex visual patterns, such as plaids composed of two superimposed drifting gratings. To compute the direction of pattern motion, MT neurons combine component motion signals over time and space. To determine the spatial and temporal limits of signal integration, we measured the responses of single MT neurons to a novel set of "pseudoplaid" stimuli in which the component gratings were alternated in time or space. As the temporal or spatial separation of the component gratings increased, neuronal selectivity for the direction of pattern motion decreased. Using descriptive models of signal integration, we inferred the temporal and spatial structure of the mechanisms that compute pattern direction selectivity. The median time constant for integration was roughly 10 ms, a timescale characteristic of integration by single cortical pyramidal neurons. The median spatial integration field was roughly one-third of the MT receptive field diameter, suggesting that the spatial limits are set by stages of processing in earlier areas of visual cortex where receptive fields are smaller than in MT. Interestingly, pattern direction-selective neurons had shorter temporal integration times than component direction-selective neurons but similar spatial integration windows. We conclude that pattern motion can only be signaled by MT neurons when the component motion signals co-occur within relatively narrow spatial and temporal limits. We interpret these results in the framework of recent hierarchical models of MT. [ABSTRACT FROM AUTHOR]

Motion perception is a pervasive nature of vision and is affected by both immediate pattern of sensory inputs and prior experiences acquired through associations. Recently, several studies reported that an association can be established quickly between directions of visual motion and static sounds of distinct frequencies. After the association is formed, sounds are able to change the perceived direction of visual motion. To determine whether such rapidly acquired audiovisual associations and their subsequent influences on visual motion perception are dependent on the involvement of higher- order attentive tracking mechanisms, we designed psychophysical experiments using regular and reverse-phi random dot motions isolating low-level pre-attentive motion processing. Our results show that an association between the directions of low-level visual motion and static sounds can be formed and this audiovisual association alters the subsequent perception of low-level visual motion. These findings support the view that audiovisual associations are not restricted to high-level attention based motion system and early-level visual motion processing has some potential role. [ABSTRACT FROM AUTHOR]

In a variety of species locomotor activity, like walking or flying, has been demonstrated to alter visual information processing. The neuromodulator octopamine was shown to change the response characteristics of optic-flow processing neurons in the fly’s visual system in a similar way as locomotor activity. This modulation resulted in enhanced neuronal responses, in particular during sustained stimulation with high temporal frequencies, and in shorter latencies of responses to abrupt onsets of pattern motion. These state-dependent changes were interpreted to adjust neuronal tuning to the range of high velocities encountered during locomotion. Here we assess the significance of these changes for the processing of optic flow as experienced during flight. Naturalistic image sequences were reconstructed based on measurements of the head position and gaze direction of Calliphora vicina flying in an arena. We recorded the responses of the V1 neuron during presentation of these image sequences on a panoramic stimulus device (FliMax). Consistent with previous accounts, we found that spontaneous as well as stimulus-induced spike rates were increased by an octopamine agonist and decreased by an antagonist. Moreover, a small but consistent decrease in response latency upon octopaminergic activation was present, which might support fast responses to optic flow cues and limit instabilities during closed-loop optomotor regulation. However, apart from these effects the similarities between the dynamic response properties in the different pharmacologically induced states were surprisingly high, indicating that the processing of naturalistic optic flow is not fundamentally altered by octopaminergic modulation.

Registration of ego-motion is important to accurately navigate through space. Movements of the head and eye relative to space are registered through the vestibular system and optical flow, respectively. Here, we address three questions concerning the visual registration of self-rotation. 1. Eye-in-head movements provide a link between the motion signals received by sensors in the moving eye and sensors in the moving head. How are these signals combined into an ego-rotation percept? We combined optic flow of simulated forward and rotational motion of the eye with different levels of eye-in-head rotation for a stationary head. We dissociated simulated gaze rotation and head rotation by different levels of eye-in-head pursuit.We found that perceived rotation matches simulated head- not gaze-rotation. This rejects a model for perceived self-rotation that relies on the rotation of the gaze line. Rather, eye-in-head signals serve to transform the optic flow’s rotation information, that specifies rotation of the scene relative to the eye, into a rotation relative to the head. This suggests that transformed visual self-rotation signals may combine with vestibular signals.2. Do transformed visual self-rotation signals reflect the arrangement of the semicircular canals (SCC)? Previously, we found sub-regions within MST and V6+ that respond to the speed of the simulated head rotation. Here, we re-analyzed those BOLD signals for the presence of a spatial dissociation related to the axes of visually simulated head rotation, such as have been found in sub-cortical regions of various animals. Contrary, we found a rather uniform BOLD response to simulated rotation along the three SCC axes.3. We investigated if subject’s sensitivity to the direction of the head rotation axis shows SCC axes specifcity. We found that sensitivity to head rotation is rather uniformly distributed, suggesting that in human cortex, visuo-vestibular integration is not arranged into the SCC frame.

Consistent with the dorsal stream hypothesis, difficulties processing dynamic information have previously been reported in individuals with autism spectrum conditions (ASC). However, no research has systematically compared motion processing abilities for slow and fast speeds. Here, we measured speed discrimination thresholds and motion coherence thresholds in slow (1.5 deg/sec) and fast (6 deg/sec) speed conditions in children with an ASC aged 7 to 14 years, and age- and ability-matched typically developing children. Unexpectedly, children with ASC were as sensitive as typically developing children to differences in speed at both slow and fast reference speeds. Yet, elevated motion coherence thresholds were found in children with ASC, but in the slow stimulus speed condition only. Rather than having pervasive difficulties in motion processing, as predicted by the dorsal stream hypothesis, these results suggest that children with ASC have a selective difficulty in extracting coherent motion information specifically at slow speeds. Understanding the effects of stimulus parameters such as stimulus speed will be important for resolving discrepancies between previous studies examining motion coherence thresholds in ASC and also for refining theoretical models of altered autistic perception. [ABSTRACT FROM AUTHOR]

Abstract: In the motion aftereffect (MAE), adapting to a moving stimulus causes a subsequently presented stationary stimulus to appear to move in the opposite direction. Recently, the neural basis of the motion aftereffect has received considerable interest, and a number of brain areas have been implicated in the generation of the illusory motion. Here, we use functional magnetic resonance imaging in combination with multivariate pattern classification to directly compare the neural activity evoked during the observation of both real and illusory motions. We show that the perceived illusory motion is not encoded in the same way as real motion in the same direction. Instead, suppression of the adapted direction of motion results in a shift of the population response of motion sensitive neurons in area MT+, resulting in activation patterns that are in fact more similar to real motion in orthogonal, rather than opposite directions. Although robust motion selectivity was observed in visual areas V1, V2, V3, and V4, this MAE-specific modulation of the population response was only observed in area MT+. Implications for our understanding of the motion aftereffect, and models of motion perception in general, are discussed. [Copyright &y& Elsevier]

In a variety of species locomotor activity, like walking or flying, has been demonstrated to alter visual information processing. The neuromodulator octopamine was shown to change the response characteristics of optic flow processing neurons in the fly's visual system in a similar way as locomotor activity. This modulation resulted in enhanced neuronal responses, in particular during sustained stimulation with high temporal frequencies, and in shorter latencies of responses to abrupt onsets of pattern motion. These state-dependent changes were interpreted to adjust neuronal tuning to the range of high velocities encountered during locomotion. Here we assess the significance of these changes for the processing of optic flow as experienced during flight. Naturalistic image sequences were reconstructed based on measurements of the head position and gaze direction of Calliphora vicina flying in an arena. We recorded the responses of the V1 neuron during presentation of these image sequences on a panoramic stimulus device ("FliMax"). Consistent with previous accounts, we found that spontaneous as well as stimulus-induced spike rates were increased by an octopamine agonist and decreased by an antagonist. Moreover, a small but consistent decrease in response latency upon octopaminergic activation was present, which might support fast responses to optic flow cues and limit instabilities during closed-loop optomotor regulation. However, apart from these effects the similarities between the dynamic response properties in the different pharmacologically induced states were surprisingly high, indicating that the processing of naturalistic optic flow is not fundamentally altered by octopaminergic modulation. [ABSTRACT FROM AUTHOR]

Abstract: Electrocorticography (ECoG) has attracted increasing interest for implementing advanced brain–computer interfaces (BCIs) in the past decade. However, real-life application of ECoG BCI demands mitigation of its invasive nature by minimizing both the size of the involved brain regions and the number of implanted electrodes. In this study, we employed a recently proposed BCI paradigm that utilizes the attentional modulation of visual motion response. With ECoG data collected from five epilepsy patients, power increase of the high gamma (60–140Hz) frequency range was found to be associated with the overtly attended moving visual stimuli in the parietal-temporal-occipital junction and the occipital cortex. Event-related potentials (ERPs) were elicited as well but with broader cortical distribution. We achieved significantly higher BCI classification accuracy by employing both high gamma and ERP responses from a single ECoG electrode than by using ERP responses only (84.22±5.54% vs. 75.48±4.18%, p <0.005, paired t-test, 3-trial averaging, binary results of attended vs. unattended). More importantly, the high gamma responses were located within brain regions specialized in visual motion processing as mapped by fMRI, suggesting the spatial location for electrode implantation can be determined prior to surgery using non-invasive imaging. Our findings demonstrate the feasibility of implementing a minimally invasive ECoG BCI. [Copyright &y& Elsevier]

Recent imaging studies in human subjects have demonstrated representations of global visual motion in medial parieto-occipital cortex (area V6) and posterior parietal cortex, the latter containing at least seven topographically organized areas along the intraparietal sulcus (IPS0-IPS5, SPL1). In this fMRI study we used topographic mapping procedures to delineate a total of 18 visual areas in human cerebral cortex and tested their responsiveness to coherent visual motion under conditions of controlled attention and fixation. Preferences for coherent visual motion as compared to motion noise as well as hemispheric asymmetries were assessed for contralateral, ipsilateral, and bilateral visual motion presentations. Except for areas V1-V4 and IPS3-5, all other areas showed stronger responses to coherent motion with the most significant activations found in V6, followed by MT/MST, V3A, IPS0-2 and SPL1. Hemispheric differences were negligible altogether suggesting that asymmetries in parietal cortex observed in cognitive tasks do not reflect differences in basic visual response properties. Interestingly, areas V6, MST, V3A, and areas along the intraparietal sulcus showed specific representations of coherent visual motion not only when presented in the hemifield primarily covered by the given visual representation but also when presented in the ipsilateral visual field. This finding suggests that coherent motion induces a switch in spatial representation in specialized motion areas from contralateral to full-field coding. [ABSTRACT FROM AUTHOR]

We recorded simultaneously from pairs of motion-sensitive neurons in the middle temporal cortex (MT) of macaque monkeys and used cross-correlations in the timing of spikes between neurons to gain insights into cortical circuitry. We characterized the time course and stimulus dependency of the cross-correlogram (CCG) for each pair of neurons and of the auto-correlogram (ACG) of the individual neurons. For some neuron pairs, the CCG showed negative flanks that emerged next to the central peak during stimulus-driven responses. Similar negative flanks appeared in the ACG of many neurons. Negative flanks were most prevalent and deepest when the neurons were driven to high rates by visual stimuli that moved in the neurons' preferred directions. The temporal development of the negative flanks in the CCG coincided with a parallel, modest reduction of the noise correlation between the spike counts of the neurons. Computational analysis of a model cortical circuit suggested that negative flanks in the CCG arise from the excitation-triggered mutual cross-inhibition between pairs of excitatory neurons. Intracortical recurrent inhibition and afterhyperpolarization caused by intrinsic outward currents, such as the calcium-activated potassium current of small conductance, can both contribute to the negative flanks in the ACG. In the model circuit, stronger intracortical inhibition helped to maintain the temporal precision between the spike trains of pairs of neurons and led to weaker noise correlations. Our results suggest a neural circuit architecture that can leverage activity-dependent intracortical inhibition to adaptively modulate both the synchrony of spike timing and the correlations in response variability. [ABSTRACT FROM AUTHOR]

Abstract: There is a long history of attempts to disentangle different visual processing mechanisms for physically different motion cues. However, underlying neural correlates and separability of networks are still under debate. We aimed to refine the current understanding by studying differential vulnerabilities when normal neural functioning is challenged. We investigated effects of ageing and extrastriate brain lesions on detection thresholds for motion defined by either luminance- or contrast modulations, known as first- and second-order motion. Both approaches focus on extrastriate processing changes and combine distributed as well as more focal constraints. Our ageing sample comprised 102 subjects covering an age range from 20 to 82 years. Threshold signal-to-noise ratios for detection approximately doubled across the age range for both motion types. Results suggest that ageing affects perception of both motion types to an equivalent degree and thus support overlapping processing resources. Underlying neural substrates were further qualified by testing perceptual performance of 18 patients with focal cortical brain lesions. We determined selective first-order motion deficits in three patients, selective second-order motion deficits in only one patient, and deficits for both motion types in three patients. Lesion analysis yielded support for common functional substrates in higher cortical regions. Functionally specific substrates remained ambiguous, but tended to cover earlier visual areas. We conclude that observed vulnerabilities of first- and second-order motion perception provide limited evidence for functional specialization at early extrastriate stages, but emphasize shared processing pathways at higher cortical levels. [Copyright &y& Elsevier]

The detection of coherent motion embedded in noise has been widely used as a measure of global visual motion processing. Animal studies have demonstrated that this performance is closely linked to the responses of direction-sensitive neurons in the macaque middle temporal (MT) and medial superior temporal (MST) areas. Despite the strong similarities between the visual cortex of human and that of non-human primates, the human middle temporal complex (area MT+), located in the posterior part of the inferior temporal sulcus and presumably comprising both area MT and area MST, has not consistently been found to share the functional hallmark of MT and MST neurons, i.e. their preference for coherent rather than incoherent visual motion. In order to search for such preferences in human area MT+, blood oxygen level-dependent responses to random dot kinematograms presented in the right visual hemifield were studied here as a function of stimulus size and dot density. The stimulus extensions were varied in such a way as to cover an area either equaling, exceeding or falling below the mean receptive field size of macaque area MT. Unlike the posterior part of human area MT+, the anterior part and its right-hemisphere homolog showed significantly stronger responses to coherent than to incoherent motion. These differences were only present for large stimuli that presumably exceeded the receptive field size of neurons in area MT. Our results suggest that functional magnetic resonance imaging may reveal stronger responses to coherent visual motion in human area MST, provided that the stimulus allows for sufficient summation within the receptive fields. In contrast, functional magnetic resonance imaging may fail to reveal the same dependency for human area MT. [ABSTRACT FROM AUTHOR]

Recent imaging studies have shown that the human posterior parietal cortex (PPC) contains four topographically organized areas along the intraparietal sulcus (IPS1-IPS4). Using a memory-guided saccade paradigm, we confirmed the locations and retinotopic organization of IPS1-IPS4 and identified two additional areas, IPS5 and superior parietal lobule 1 (SPL1). IPS5 is located at the intersection of the intraparietal and postcentral sulcus; SPL1 branches off the IPS and extends into the superior parietal lobule. Both areas, as well as IPS1-IPS4, each contain a representation of the contralateral visual hemifield. We then probed core functions of the dorsal pathway in these areas, that is, the representation of eye movements and visual motion, to compare the functional characteristics of human PPC to physiologically and anatomically defined areas in monkey PPC. First, as in monkey PPC, a gradient representation of eye movements was found along the IPS with decreasing responses for saccades and increasing responses for smooth pursuit eye movements from posterior/medial to anterior/lateral. The greatest preference for saccades was found in SPL1 and for smooth pursuit in IPS5. Second, and again similar to monkey PPC, all topographically organized PPC areas responded to different types of motion including planar, circular, and radial optic flow, as assessed using adaptation paradigms. Areas in posterior IPS preferred radial optic flow over planar motion, whereas areas in anterior PPC did not show preference for a particular motion type. Together, our results indicate strikingly similar characteristics in the general functional organization of human and monkey PPC, but also reveal some notable differences. [ABSTRACT FROM AUTHOR]

Abstract: It is well established that elementary motion detectors are only able to code for the movement of a contour perpendicular to its orientation. This shortcoming explains why the initial direction of smooth-pursuit eye movements is directed orthogonal to the orientation of a moving contour independent of its veridical direction of motion. Here, we replicated this finding and asked whether this directional error can be reduced by subjects’ prediction of upcoming target moving direction and whether this directional error also occurs during tracking of an illusory contour. Our results show that prediction did not abolish the directional error, it was only slightly reduced. On the other hand, the directional error was considerably diminished during pursuit initiation towards illusory contours and most likely reflected the amount of real stimulation defining the specific illusory contour. We conclude that pursuit initiation is driven by raw retinal image motion signals, which are not yet processed for figure completion. [Copyright &y& Elsevier]

We recorded the responses of direction-selective simple and complex cells in the primary visual cortex (V1) of anesthetized, paralyzed macaque monkeys. When studied with sine-wave gratings, almost all simple cells in V1 had responses that were separable for spatial and temporal frequency: the preferred temporal frequency did not change and preferred speed decreased as a function of the spatial frequency of the grating. As in previous recordings from the middle temporal visual area (MT), approximately one-quarter of V1 complex cells had separable responses to spatial and temporal frequency, and one-quarter were "speed tuned" in the sense that preferred speed did not change as a function of spatial frequency. Half fell between these two extremes. Reducing the contrast of the gratings caused the population of V1 complex cells to become more separable in their tuning for spatial and temporal frequency. Contrast dependence is explained by the contrast gain of the neurons, which was relatively higher for gratings that were either both of high or both of low temporal and spatial frequency. For stimuli that comprised two spatially superimposed sine-wave gratings, the preferred speeds and tuning bandwidths of V1 neurons could be predicted from the sum of the responses to the component gratings presented alone, unlike neurons in MT that showed nonlinear interactions. We conclude that spatiotemporal modulation of contrast gain creates speed tuning from separable inputs in V1 complex cells. Speed tuning in MT could be primarily inherited from V1, but processing that occurs after V1 and possibly within MT computes selective combinations of speed-tuned signals of special relevance for downstream perceptual and motor mechanisms. [ABSTRACT FROM AUTHOR]

The magnocellular system plays an important role in visual motion processing, controlling vergence eye movements, and in reading. Yellow filters may boost magnocellular activity by eliminating inhibitory blue input to this pathway. It was found that wearing yellow filters increased motion sensitivity, convergence, and accommodation in many children with reading difficulties, both immediately and after three months using the filters. Motion sensitivity was not increased using control neutral density filters. Moreover, readingimpaired children showed significant gains in reading ability after three months wearing the filters compared with those who had used a placebo. It was concluded that yellow filters can improve magnocellular function permanently. Hence, they should be considered as an alternative to corrective lenses, prisms, or exercises for treating poor convergence and accommodation, and also as an aid for children with reading problems. [ABSTRACT FROM AUTHOR]

Both perceptual and motor systems must decode visual information from the distributed activity of large populations of cortical neurons. We have sought a common framework for understanding decoding strategies for visually guided movement and perception by asking whether the strong motion aftereffects seen in the perceptual domain lead to similar expressions in motor output. We found that motion adaptation indeed has strong sequelae in the direction and speed of smooth pursuit eye movements. After adaptation with a stimulus that moves in a given direction for 7 sec, the direction of pursuit is repelled from the direction of pursuit targets that move within 90° of the adapting direction. The speed of pursuit decreases for targets that move at the direction and speed of the adapting stimulus and is repelled from the adapting speed in the sense that the decrease either becomes greater or smaller (eventually turning to an increase) when tracking targets move slower or faster than the adapting speed. The effects of adaptation are spatially specific and fixed to the retinal location of the adapting stimulus. The magnitude of adaptation of pursuit speed and direction is uncorrelated, suggesting that the two parameters are decoded independently. Computer simulation of motion adaptation in the middle temporal visual area (MT) shows that vector-averaging decoding of the population response in MT can account for the effects of adaptation on the direction of pursuit. Our results suggest a unified framework for thinking, in terms of population decoding, about motion adaptation for both perception and action. [ABSTRACT FROM AUTHOR]

To guide behavior, perceptual and motor systems must estimate properties of the sensory environment from the responses of populations of cortical neurons. In the domain of visual motion, estimates of target speed are derived from the responses of motion-sensitive neurons in the middle temporal (MT) area of the extrastriate visual cortex and are used to drive smooth pursuit eye movements and perceptual judgments of speed. We have asked how these behavioral systems estimate target speed from the population response in area MT. We found that increasing the spatial frequency of a sine wave grating caused decreases in the target speed estimated by both pursuit and perception and commensurate changes in the identity of the active neurons in area MT. Decreasing the contrast of a sine wave grating caused decreases in the target speed estimated by both pursuit and perception, while altering only the response amplitude of MT neurons and not the identity of the active neurons. Applying a modified vector-averaging computation to the population response measured in area MT allowed us to predict the effects of both spatial frequency and contrast on speed estimation for both perception and pursuit. The modification biased the speed estimation toward low target speeds when responses across the population of neurons were small. [ABSTRACT FROM AUTHOR]

Variable behavioral responses to identical visual stimuli can, in part, be traced back to variable neuronal signals that provide unreliable information about the outside world. This unreliability in encoding of visual information is caused by several noise sources such as photon noise, synaptic noise, or the stochastic nature of ion channels. Neurons of the fly's visual motion pathway have been claimed to represent perfect encoders, with photon noise as the main noise source limiting their performance. Other studies on the fly's visual system suggest, however, that internal noise emerging within the nervous system also affects the reliability of motion vision. To resolve these contradictory interpretations, we performed an electrophysiological investigation, inspired by the "equivalent noise" paradigm applied in psychophysics, on the fly's motion-sensitive H1 neuron. Noise-like brightness fluctuations of different strength were superimposed on the motion stimuli. Because the noise level found to affect the temporal properties of the spike responses is much larger than the estimate of photon noise under the experhymental conditions, our results indicate that motion vision is more likely to be limited by internal sources of variability than by photon noise. [ABSTRACT FROM AUTHOR]

Abstract For the detection of a moving object, segregating the object from the background is a necessary first step. This segregation can be achieved by detection of differences in the spatial, temporal and spatio-temporal properties of the object and background. Here we investigate how flicker influences the perception of a moving object in man and monkey, and we examine the neuronal responses in extrastriate medial temporal and medial superior temporal areas (MT and MST) of two rhesus monkeys. The performance of humans and monkeys in a direction discrimination task was impaired in the presence of flicker in the background compared to the static background condition. A similar effect was found in recordings from 155 single units in areas MT and MST during the discrimination task. The discriminability (d ′) of the neuronal responses in preferred and nonpreferred directions was reduced by 33% on average in the presence of a flicker background compared to the static background. This reduction in discriminability was not caused by differences in variance of the neuronal activity for the two background conditions, but was due to a reduction of the difference between the activities in preferred and nonpreferred direction. This reduction in directional selectivity could be traced back to two different mechanisms: in 32 out of 155 neurons (21%), the decrease resulted from an increase in the response to the stimulus moving in the nonpreferred direction; in 62 out of 155 neurons (40%), the reduction in directional selectivity was due to a decrease in the response to the preferred direction. These results give deeper insights into how moving stimuli are processed in the presence of background flicker as present in natural visual scenes. [ABSTRACT FROM AUTHOR]

We have evaluated the use of visual information about the movement of a target in two tasks tracking and interceptions - involving multi-joint reaching movements with the arm. Target velocity was either varied in a pseudorandom order (random condition) or was kept constant (predictable condition) across trials. Response latency decreased as target velocity increased in each condition. A simple model that assumes that latency is the sum of two components - the time taken for target motion to be detected, and a fixed processing time - provides a good fit to the data. Results from a step-ramp experiment, in which the target stepped a small distance immediately preceding the onset of the ramp motion, were consistent with this model. The characteristics of the first 100 ms of the response depended on the amount of information about target motion available to the subject. In the tracking task with randomly varied target velocities, the initial changes in hand velocity were largely independent of target velocity. In contrast, when the velocity was predictable the initial hand velocity depended on target velocity. Analogously, the initial changes in the direction of hand motion in the interception task were independent of target velocity in the random condition, but depended on target velocity in the predictable condition. The time course for development of response dependence was estimated by controlling the amount of visual information about target velocity available to the subject before the onset of limb movement. The results suggest that when target velocity was random, hand movement started before visual motion processing was complete. The response was subsequently adjusted after target velocity was computed. Subjects displayed idiosyncratic strategies during the catch-up phase in the tracking task. The peak hand velocity depended on target velocity and was similar for all subjects. The time at which the peak occurred, in contrast, varied substantially among subjects. In the interception task the hand paths were straighter in the predictable than in the random condition. This appeared to be the result of making adjustments in movement direction in the former condition to correct for initially inappropriate responses. [ABSTRACT FROM AUTHOR]

A wide range of experimental data characterizing propertiesof individual salamander retinal cells and synaptic interactionsare integrated to form a quantitative computational model of visual function in the salamander retina.The model is used to show how specific interactions between neuronsand between networks of neurons can lead to the integratedresponse behavior of individual cells deep in the retina. Themodel is also used to illustrate how the representation of movingand stationary stimuli is encoded in a series of layer-by-layertransformations leading to the final retinal output at the ganglioncell layer. [ABSTRACT FROM AUTHOR]