选择题：For some time past it has been widely accepted tha

For some time past it has been widely accepted that babies and other creatures learn to do things
because certain acts lead to " rewards";and there is no reason to doubt that this is true.But it used also to be widely believed that effective rewards,at least in the early stages,had to be directly related to such basic physiological"drives"as thirst or hunger.In other words,a baby would learn if he got food
or drink or some sort of physical comfort,not otherwise.It is now clear that this is not so.Babies will learn to behave in ways that produce results in the world with no reward except the successful outcome.
Papousek began his studies by using milk in the normal way to"reward"the babies and so teach
them to carry out some simple movements,such as turning the head to one side or the other.Then he
noticed that a baby who had had enough to drink would refuse the milk but would still go on making the learned response with clear signs of pleasure.So he began to study the children.s responses in situations where no milk was provided.He quickly found that children as young as four months would learn to turn their heads to right or left if the movement"switched on"a display of lights-and indeed that they were
capable of learning quite complex turns to bring about this result.For instance,two left or two right,or even to make as many as three turns to one side.Papousek.s light d