Piaget maintained a child's first interactions with the world is through her senses. Mimicking a child's need to feed, children's initial sensory experience of the world is through suckling objects, from bottles or the nipples of their mothers to fingers, blocks and other tangible objects. From suckling, children move onto visual experience. The information gathered from sensory experience allows the child to learn about her relation to other objects in the world and form an understanding of herself as a being distinct from her environment -- unlike her time in the womb, in which she and her environment were the same.
In experiencing the world, Piaget believed children naturally develop the ability to reflexively react to certain experiences. The best indicator of how children learn to reflexively respond to stimuli exists in a popular experiment undertaken by Piaget, as well as many parents, in which a baby is given a lemon on which to suckle. Because of the sourness of the lemon, babies initially respond negatively to the taste, but will continue to suckle it. Eventually, as the process is repeated, children learn to throw the lemon away from themselves. In this situation, the reflex is not the sour face pulled by the children, but the throwing away of the lemon.
As children catalog their reflexive responses to certain sensory experiences, they direct their attention toward or away from those experiences. For example, as children learn to reflexively associate their mother with feeding, they may demonstrate an ability to call for their mother, an expression of voluntary desire. Similarly, as with the lemon example, children learn to voluntarily avoid lemons, given their understanding of its sour taste.
Later in the preoperational stage, Piaget believed some children were able to translate their voluntary actions into symbolic thoughts as a way to solve problems. For example, as children learn to voluntarily cry for their mothers, they come to associate crying with reward, namely the reward of their mother coming to care for them. Upon learning this association, children begin to cry whenever they want to be rewarded by a parent's care, which shows evidence of rudimentary symbolic and problem-solving thought.