Eye–hand coordination

Eye hand coordination (also known as hand–eye coordination) is the coordinated control of eye movement with hand movement and the processing of visual input to guide reaching and grasping along with the use of proprioception of the hands to guide the eyes. Eye–hand coordination has been studied in activities as diverse as the movement of solid objects such as wooden blocks, archery, sporting performance, music reading, computer gaming, copy-typing, and even tea-making. It is part of the mechanisms of performing everyday tasks; in its absence, most people would be unable to carry out even the simplest of actions such as picking up a book from a table or playing a video game. While it is recognized by the term hand–eye coordination, without exception, medical sources, and most psychological sources, refer to eye–hand coordination. Eye hand coordination (also known as hand–eye coordination) is the coordinated control of eye movement with hand movement and the processing of visual input to guide reaching and grasping along with the use of proprioception of the hands to guide the eyes. Eye–hand coordination has been studied in activities as diverse as the movement of solid objects such as wooden blocks, archery, sporting performance, music reading, computer gaming, copy-typing, and even tea-making. It is part of the mechanisms of performing everyday tasks; in its absence, most people would be unable to carry out even the simplest of actions such as picking up a book from a table or playing a video game. While it is recognized by the term hand–eye coordination, without exception, medical sources, and most psychological sources, refer to eye–hand coordination. Neuroscientists have extensively researched human gaze behavior, with studies noting that the use of the gaze is very task-specific, but that humans typically exhibit proactive control to guide their movement. Usually, the eyes fixate on a target before the hands are used to engage in a movement, indicating that the eyes provide spatial information for the hands. The duration that the eyes appear to be locked onto a goal for a hand movement varies—sometimes the eyes remain fixated until a task is completed. Other times, the eyes seem to scout ahead toward other objects of interest before the hand even grasps and manipulates the object. When eyes and hands are used for core exercises, the eyes generally direct the movement of the hands to targets. Furthermore, the eyes provide initial information of the object, including its size, shape, and possibly grasping sites that are used to determine the force the fingertips need to exert to engage in a task. For sequential tasks, eye-gaze movement occurs during important kinematic events like changing the direction of a movement or when passing perceived landmarks. This is related to the task-search-oriented nature of the eyes and their relation to the movement planning of the hands and the errors between motor signal output and consequences perceived by the eyes and other senses that can be used for corrective movement. The eyes have a tendency to 'refixate' on a target to refresh the memory of its shape, or to update for changes in its shape or geometry in drawing tasks that involve the relating of visual input and hand movement to produce a copy of what was perceived. In high accuracy tasks, when acting on greater amounts of visual stimuli, the time it takes to plan and execute movement increases linearly, per Fitts's law. Humans have demonstrated the ability to aim eye movement toward the hand without vision, using the sense of proprioception, with only minor errors related to internal knowledge of limb position. It has been shown the proprioception of limbs, in both active and passive movement, result in eye saccade overshoots when the hands are being used to guide eye movement. These overshoots result from the control of eye saccades rather than previous movement of the hands in experiments. This implies that limb-based proprioception is capable of being transformed into ocular motor coordinates to guide eye saccades, which allows for the guidance of the saccades by hands and feet. The neural control of eye–hand coordination is complex because it involves every part of the central nervous system involved in vision: eye movements, touch, and hand control. This includes the eyes themselves, the cerebral cortex, subcortical structures (such as the cerebellum, basal ganglia, and brain stem), the spinal cord, and the peripheral nervous system. Other areas involved in eye–hand coordination that have been studied most intensely are the frontal and parietal cortex areas for the control of eye saccades and hand-reach. Both of these areas are believed to play a key role in eye–hand coordination and the planning of movements during tasks. A more specific area, the parieto occipital junction, is believed to be involved in the transformation of peripheral visual input for reaching with the hands, as found via fMRI. This region in particular has subdivisions for reach, grasp, and saccades. In addition to the parieto–occipital junction, the posterior parietal cortex is believed to play an important role in relating proprioception and the transformation of motor sensory input to plan and control movement with regard to visual input. Many of these areas, in addition to controlling saccades or reach, also show eye position signals that are required for transforming visual signals into motor commands. In addition, some of the areas involved in reach, like the medial intraparietal cortex, show a gaze-centered remapping of responses during eye movements in both monkeys and humans. However, when single neurons are recorded in these areas, the reach areas often show some saccade-related responses and the saccade areas often show some reach related responses. This may aid in eye–hand coordination or hint at the ability of cells to wire together as they're used more frequently.