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Interaction with visual objects in the environment requires an accurate correspondence between visual space and its internal representation within the brain. Many clinical conditions involve some impairment in visuo-motor control and the errors created by the lesion of a specific brain region are neither random nor uninformative. Modern approaches to studying the neuropsychology of action require powerful data-driven analyses and error modelling in order to understand the function of the lesioned areas. In the present paper we carried out mixed-effect analyses of the pointing errors of seven optic ataxia patients and seven control subjects. We found that a small parameter set is sufficient to explain the pointing errors produced by unilateral optic ataxia patients. In particular, the extremely stereotypical errors made when pointing toward the contralesional visual field can be fitted by mathematical models similar to those used to model central magnification in cortical or sub-cortical structure(s). Our interpretation is that visual areas that contain this footprint of central magnification guide pointing movements when the posterior parietal cortex is damaged and that the functional role of the posterior parietal cortex is to actively compensate for the under-representation of peripheral vision that accompanies central magnification. Optic ataxia misreaching reveals what would be hand movement accuracy and precision if the human motor system did not include elaborated corrective processes for reaching and grasping to non-foveated targets.

Interaction with visual objects in the environment requires an accurate correspondence between visual space and its internal representation within the brain. Many clinical conditions involve some impairment in visuo-motor control and the errors created by the lesion of a specific brain region are neither random nor uninformative. Modern approaches to studying the neuropsychology of action require powerful data-driven analyses and error modeling in order to understand the function of the lesioned areas. In the present paper we carried out mixed-effect analyses of the pointing errors of seven optic ataxia patients and seven control subjects. We found that a small parameter set is sufficient to explain the pointing errors produced by unilateral optic ataxia patients. In particular, the extremely stereotypical errors made when pointing toward the contralesional visual field can be fitted by mathematical models similar to those used to model central magnification in cortical or sub-cortical structure(s). Our interpretation is that visual areas that contain this footprint of central magnification guide pointing movements when the posterior parietal cortex (PPC) is damaged and that the functional role of the PPC is to actively compensate for the under-representation of peripheral vision that accompanies central magnification. Optic ataxia misreaching reveals what would be hand movement accuracy and precision if the human motor system did not include elaborated corrective processes for reaching and grasping to non-foveated targets. [ABSTRACT FROM AUTHOR]

Purpose The progress of learning human movements and motor control mechanisms by observing and imitating human movements was based on visuomotor control in three-dimensional (3D) space. However, previous studies of motion control in 3D space have focused on analyzing tracking tasks along 1D lines or 2D planes using single or multi-joint movements. In this study, we propose a visuomotor system for quantitatively evaluating visuomotor control in a 3D space based on virtual reality (VR) (Choi (2018)). The proposed system has been designed to analyze 3D circular tracking motions on frontal and sagittal planes of VR space. Furthermore, we analyzed two types of 3D target tracking tasks to verify the effectiveness of our system, the 3D circular tracking movements from the frontal plane to the body and the circular tracking movements from the sagittal plane to the body. In addition, we compared visuomotor control in 3D circular tracking motion between monocular without depth and binocular vision with depth. Method The system allowed users to conduct the 3D visually-guided tracking movement in the 3D VR space (Figure 1). We established the size of the 3D target as 1.5 times larger than the 3D tracer in this research. The 3D target has a red ball with a radius of 1.5 cm. The 3D tracer has a yellow ball with a radius of 1 cm placed at the tip of the 3D stick. Instead of users' own hands in VR space, the hands were shown the 3D stick. Each task was carried out with the 3D target rotating on the frontal plane (ROTO in Figure 1(A)) and on the sagittal plane (ROT90 in Figure 1(B)). We transformed the data of the X, Y, and Z to "R" displacement, "ϑ" angular displacement, and "ω" angular velocity on polar coordinates. We analyzed the differences of 3D circular tracking movements based on the parameters of ΔR, Δϑ, and Δω in VR space (Choi (2020)). Results and Discussion We developed a system that allows users to quantitatively evaluate visuomotor movement based on 3D target tracking in a 3D virtual reality space. It is verified that 3D visuomotor control under monocular and binocular conditions could be analyzed quantitatively. We found that the tracking system is more useful to adopt the parameters of Δϑ, and Δω to analyze the circular tracking movement with increasing speed. In addition, we also found that the parameter of ΔR was not suitable for the analysis of low-speed movement. When tracking movement, we also found that the visual dependence was large and had a great influence on the accuracy of the movement. The proposed system can be useful for assessing the severity of the disease and the rehabilitation of people with hemiplegic upper arms. The proposed system can also quantitatively measure the performance of the visuomotor control system of aging adults and create a database of the visuomotor control. This study will contribute to a basic research to analyze the changes of the visuomotor control system that occur with aging and to present an appropriate motor learning model for aging adults. [ABSTRACT FROM AUTHOR]

A successful catch of a falling ball requires an accurate estimation of the timing for when the ball hits the hand. In a previous experiments in which participants performed ball-catching task in virtual reality environment, we accidentally found that the weight of a falling ball was perceived differently when the timing of ball load force to the hand was shifted from the timing expected from visual information. Although it is well known that spatial information of an object, such as size, can easily deceive our perception of its heaviness, the relationship between temporal information and perceived heaviness is still not clear. In this study, we investigated the effect of temporal factors on weight perception. We conducted ball-catching experiments in a virtual environment where the timing of load force exertion was shifted away from the visual contact timing (i.e., time when the ball hit the hand in the display). We found that the ball was perceived heavier when force was applied earlier than visual contact and lighter when force was applied after visual contact. We also conducted additional experiments in which participants were conditioned to one of two constant time offsets prior to testing weight perception. After performing ball-catching trials with 60 ms advanced or delayed load force exertion, participants' subjective judgment on the simultaneity of visual contact and force exertion changed, reflecting a shift in perception of time offset. In addition, timing of catching motion initiation relative to visual contact changed, reflecting a shift in estimation of force timing. We also found that participants began to perceive the ball as lighter after conditioning to 60 ms advanced offset and heavier after the 60 ms delayed offset. These results suggest that perceived heaviness depends not on the actual time offset between force exertion and visual contact but on the subjectively perceived time offset between them and/or estimation error in force timing.

The present study investigated the enhancement effects of an external focus-of-attention (FOA) in the context of a manual-tracking task, in which participants tracked both visible and occluded targets. Three conditions were compared, which manipulated the distance of the FOA from the participant as well as the external/internal dimension. As expected, an external FOA resulted in lower tracking errors than an internal FOA. In addition, analyses of participants' movement patterns revealed a systematic shift toward higher-frequency movements in the external FOA condition, consistent with the idea that an external FOA exploits the natural movement dynamics available during skilled action. Finally, target visibility did not influence the effect of focused attention on tracking performance, which provides evidence for the proposal that the mechanisms that underlie FOA do not depend directly on vision.

Abstract: By 1985 newly devised behavioural and electrophysiological techniques had been used to track development of infants’ acuity, contrast sensitivity and binocularity, and for clinical evaluation of developing visual function. This review focusses on advances in the development and assessment of infant vision in the following 25years. Infants’ visual cortical function has been studied through selectivity for orientation, directional motion and binocular disparity, and the control of subcortical oculomotor mechanisms in fixation shifts and optokinetic nystagmus, leading to a model of increasing cortical dominance over subcortical pathways. Neonatal face processing remains a challenge for this model. Recent research has focussed on development of integrative processing (hyperacuity, texture segmentation, and sensitivity to global form and motion coherence) in extra-striate visual areas, including signatures of dorsal and ventral stream processing. Asynchronies in development of these two streams may be related to their differential vulnerability in both acquired and genetic disorders. New methods and approaches to clinical disorders are reviewed, in particular the increasing focus on paediatric neurology as well as ophthalmology. Visual measures in early infancy in high-risk children are allowing measures not only of existing deficits in infancy but prediction of later visual and cognitive outcome. Work with early cataract and later recovery from blinding disorders has thrown new light on the plasticity of the visual system and its limitations. The review concludes with a forward look to future opportunities provided by studies of development post infancy, new imaging and eye tracking methods, and sampling infants’ visual ecology. [Copyright &y& Elsevier]

Abstract: Baurès et al. [Baurès, R., Benguigui, N., Amorim, M.-A., & Siegler, I. A. (2007). Intercepting free falling objects: Better use Occam’s razor than internalize Newton’s law. Vision Research, 47, 2982–2991] rejected the hypothesis that free-falling objects are intercepted using a predictive model of gravity. They argued instead for “a continuous guide for action timing” based on visual information updated till target capture. Here we show that their arguments are flawed, because they fail to consider the impact of sensori-motor delays on interception behaviour and the need for neural compensation of such delays. When intercepting a free-falling object, the delays can be overcome by a predictive model of the effects of gravity on target motion. [Copyright &y& Elsevier]

Using displacing prisms to dissociate the influence of optic flow and egocentric direction, previous research (Current Biology 8 (1998) 1191) showed that people primarily use egocentric direction to control their locomotion on foot, rather than optic flow. When wearing displacing prisms, participants followed the curved path predicted by the use of simple egocentric direction, rather than a straight path, as predicted by the use of optic flow. It has previously been suggested that, in rich visual environments, other visual information including optic flow and static scene structure may influence locomotion in addition to direction. Here we report a study where neither scene structure nor optic flow have any influence on the control of walking. Participants wearing displacing prisms walked along a well-lit corridor (containing rich scene structure and flow) and along the same corridor in darkness (no scene structure or flow). Heading errors were not significantly different between the dark and light conditions. Thus, even under conditions of rich scene structure and high flow when walking in a well-lit corridor, participants follow the same curved paths as when these cues are not available. These results demonstrate that there are conditions under which visual direction is the only useful source of visual information for the control of locomotion. [Copyright &y& Elsevier]

Although it has been proposed that birds acquire visual depth cues through dynamic head movements, behavioral evidence on how birds use motion parallax depth cues caused by self-motion is lacking. This study investigated whether self-generated motion parallax modulates pecking motor control and visual size perception in pigeons ( Columba livia ). We trained pigeons to peck a target on a touch monitor and to classify it as small or large. To manipulate motion parallax of the target, we changed the target position on the monitor according to the bird's head position in real time using a custom-built head tracker with two cameras. Pecking motor control was affected by the manipulation of motion parallax: when the motion parallax signified the target position farther than the monitor surface, the head position just before pecking to target was near the monitor surface, and vice versa. By contrast, motion parallax did not affect how the pigeons classified target sizes, implying that motion parallax might not contribute to size constancy in pigeons. These results indicate that motion parallax via head movements modulates pecking motor control in pigeons, suggesting that head movements of pigeons have the visual function of accessing motion parallax depth cues., Competing Interests: Competing interestsThe authors declare no competing or financial interests., (© 2021. Published by The Company of Biologists Ltd.)

We present a new visual control input from optical flow divergence enabling the design of novel, unified control laws for docking and landing. While divergence-based time-to-contact estimation is well understood, the use of divergence in visual control currently assumes knowledge of surface orientation, and/or egomotion. There exists no directly observable visual cue capable of supporting approaches to surfaces of arbitrary orientation under general motion. Central to our measure is the use of the maximum flow field divergence on the view sphere (max-div). We prove kinematic properties governing the location of max-div, and show that max-div provides a temporal measure of proximity. From this, we contribute novel control laws for regulating both approach velocity and angle of approach toward planar surfaces of arbitrary orientation, without structure-from-motion recovery. The strategy is tested in simulation, over real image sequences and in closed-loop control of docking/landing maneuvers on a mobile platform. [ABSTRACT FROM AUTHOR]

A successful catch of a falling ball requires an accurate estimation of the timing for when the ball hits the hand. In a previous experiment in which participants performed ball-catching task in virtual reality environment, we accidentally found that the weight of a falling ball was perceived differently when the timing of ball load force to the hand was shifted from the timing expected from visual information. Although it is well known that spatial information of an object, such as size, can easily deceive our perception of its heaviness, the relationship between temporal information and perceived heaviness is still not clear. In this study, we investigated the effect of temporal factors on weight perception. We conducted ball-catching experiments in a virtual environment where the timing of load force exertion was shifted away from the visual contact timing (i.e., time when the ball hit the hand in the display). We found that the ball was perceived heavier when force was applied earlier than visual contact and lighter when force was applied after visual contact. We also conducted additional experiments in which participants were conditioned to one of two constant time offsets prior to testing weight perception. After performing ball-catching trials with 60 ms advanced or delayed load force exertion, participants' subjective judgment on the simultaneity of visual contact and force exertion changed, reflecting a shift in perception of time offset. In addition, timing of catching motion initiation relative to visual contact changed, reflecting a shift in estimation of force timing. We also found that participants began to perceive the ball as lighter after conditioning to 60 ms advanced offset and heavier after the 60 ms delayed offset. These results suggest that perceived heaviness depends not on the actual time offset between force exertion and visual contact but on the subjectively perceived time offset between them and/or estimation error in force timing.

The present study investigated the enhancement effects of an external focus of attention (FOA) in the context of a manual tracking task, in which participants tracked both visible and occluded targets. Three conditions were compared, which manipulated the distance of the FOA from the participant as well as the external/internal dimension. As expected, an external FOA resulted in lower tracking errors than an internal FOA. In addition, analyses of participants' movement patterns revealed a systematic shift toward higher-frequency movements in the external FOA condition, consistent with the idea that an external FOA exploits the natural movement dynamics available during skilled action. Finally, target visibility did not influence the effect of focused attention on tracking performance, which provides evidence for the proposal that the mechanisms that underlie FOA do not depend directly on vision.