ABSTRACT
What is an ‘action’ and where does it come from? This is a fundamental question in motor control that will be addressed in the current chapter. As infants, it is likely that we start with sensorimotor ‘babbling’ (Thelen, 1979) that, by chance, causes something to happen in the external world. The ‘baby babble’ is then gradually refi ned until the causal components embedded within the initial multidimensional movements are identifi ed. At this point, we can say that a new action has been acquired. The defi ning characteristic of an action developed in this manner is that it refers to a movement or sequence of movements that causes a predicted outcome in the external world. Thorndike reported an early example of an experiment that demonstrated the process of acquiring a novel action, the results of which led him to formulate his famous Law of Effect (Thorndike, 1911). He placed a hungry cat in a cage with a door that was held closed by a pin. A pedal in the cage was connected to the pin, so that, if the cat pressed the pedal, the pin was released and the door fell open. Outside the cage was a piece of fi sh. As the animal explored the cage to fi nd a way to the fi sh, the pedal was initially pressed ‘by accident’, i.e. with no knowledge of the outcome. At this stage, door opening was not predicted, and therefore, when it happened, was a surprise to the animal. However, through trial and error, the cat gradually discovered that the critical component of its initial exploratory behavior was to place its foot on the pedal and press. This form of learning effectively equipped the animal with a novel act (pedal press), which produced a predicted outcome (door opening giving access to the fi sh). Formally, Thorndike proposed that ‘any act which in a given situation produces satisfaction becomes associated with that situation so that when the situation recurs the act is more likely than before to recur also’ – the Law of Effect (Thorndike, 1911).
