The answer is "secondary circular reactions involve the infant responding to people
and objects in
outer world."
An example is that when a mother hands the infant a duck or something he
squeezes it, sometime creating a sound which the infant feels like responding
to and that is why he/she will repeat the action again and again.
The idea was presented by a Swiss scientist Jean Piaget and is known as Piaget's stages of
sensorimotor intelligence.
