Hand-eye 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. Conversely, humans are able to aim saccades toward the hand without vision, using spatial information from hand proprioception.

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 shorter tasks, the eyes often shift onto another task to provide additional input for planning further input is used to adjust for errors in movement and to create more precise movement.

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 as per Fitts's Law.

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