Sensory systems need two kinds input to develop: genetic
instructions and stimulation from the environment. All of the
senses except for vision are stimulated in the womb. The sense of
touch is the first sensory system to develop in the womb and is
likely the most mature at birth.
The sense of taste and smell also develop in the womb and
vision develops later because babies are born without true depth
perception, and color vision is very limited. Experiments also show
that newborns recognize the smell of amniotic fluid and they like
the scent of breast milk. Since mother's milk is sweet,and thats
the first food babies taste therefore it develops much faster than
other senses. Babies cannot taste salt until they are 4months old
but sweetness they can because of first taste they get of the
mother's milk.