Hand–eye coordination

Hand–eye coordination (also known as eye–hand coordination) is the coordinated motor 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, a modality of multisensory integration. Hand–eye 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 not be able to carry out even the simplest of actions such as picking up a book from a table. The eye–forelimb (EF) hypothesis suggests that the primate visual system changed in parallel with the specialization of the hand through a common evolutionary mechanism. The ultimate result became accurate depth perception, speed and exactness of the hand when it is gripping. Primates, including humans, have eyes that are directed forward. Primates also have an optic chiasm (OC), with 45 percent made up of uncrossed nerves. The traditional idea is that such vision combined with high-grade binocularity to promote deep vision. However, an overview article in Brain, Behavior and Evolution presents a new "Eye–forelimb hypothesis" (EF hypothesis) that suggests that the neural architecture of primates' visual system evolved for a totally different purpose. The EF hypothesis postulates that it has selective value to have short neural pathways between areas of the brain that receive visual information about the hand and the motor nuclei that control the coordination of the hand. The heart of the EF hypothesis is that evolutionary transformation in OC will affect the length of these neural pathways. A way to test the hypothesis is comparing the precision and speed of, let's say, the left hand when performing tasks in the left and right field of view respectively. Several such experiments have been carried out.