ABSTRACT
The most remarkable aspect of motor control as observed in human and animal behavior is not so much the synchronization of many muscles and joints in a complex motor act, for complex synchronization is easily achieved in man-made machines by way of cams and cogs. The unique property of biological motor control is the adaptability and generality of the motor code. The mechanical synchronization by way of cams and cogs is rigid and stereotyped, the motor control equivalent of templates in visual recognition. Much more difficult to replicate is the generality exhibited in biological motion, when the regular sequence of the motor pattern is modulated in analog fashion to avoid obstacles, or to conform a complex pattern of steps to an irregular terrain. The generality of the motor code is seen most clearly in the way that a person adapts their gait to accommodate a prosthetic leg, or crutches, or the way a waiter carrying a loaded tray opens a door with his knee, or when a man tied up by an intruder wriggles across the floor like a worm, lifts the telephone receiver with his mouth, and dials the police with his nose. This adaptability in motor representation is seen from the earliest months of development. For the patterns of motion observed in infants when they first learn to crawl varies considerably across individual infants. Some babies locomote by rolling like a log; others shuffle and scrape along the floor using a bewildering variety of strategies, much like a person tied up by a burglar. After eventually learning to walk in the conventional fashion, even young children can easily adapt to bizarre variations such as walking sideways or backward, or walking in a straight line while rotating slowly like a top.
