The sense of hearing is fairly well developed in infants at birth. In fact, it is thought that infants are able to hear sounds in the womb up to four months before birth. It is important, therefore, for parents to talk to their newborns, even though they cannot understand, to stimulate hearing development. By the end of the first month, most infants will be able to respond physically to sounds in some way, such as by startling, crying, or quieting. Newborns are probably as sensitive to taste stimulation as they will ever be at any time in their lives.
Sense of smell is present at birth, too.
During the first week of life infants' whole bodies respond to sudden changes in the environment. At this time, infants' arm, leg, and hand movements will be primarily controlled by reflexes. As children grow older, these reflexes will begin to disappear. By two months of age most actions will be voluntary, not reflexive. One such reflex that infants have at birth is the grasp reflex.