The process of learning a tool-use movement in monkeys, with special reference to vision.

Monkeys learned to use forceps to pick up food. The learning progressed in two stages. After having understood the task to have to use forceps through guidance, they (1) brought forceps toward food without seeing food until it was reached (1st stage), and (2) made forceps reach accurately to food using vision (2nd stage). We suggest that the learning without vision was a process of incorporating grasped-forceps into the body-scheme, thus enabling reaching with the extension (forceps) to a certain place in space. Using vision at the final stage was to precisely reach and to pick up food with the extension.