Explore The Auditory System in more detail :
Auditory Development from Birth
The physical structures of the ear are already completely formed by the time a baby is born. The inner ear (cochlea) is completed and begins to hear at around 25 weeks’ gestation, and fetuses will respond to loud noises with an increased heart rate then. In fact, hearing sounds (especially human voices) in utero is important to stimulate the auditory pathways between the cochlea and the brain, and the auditory parts of the brain itself.
It turns out that infants can perform an astonishing number of listening tasks successfully, such as being able to discriminate speech sounds from any of the world’s languages. Gradually, however, their auditory systems and brains learn to “tune in” to the spoken language(s) they hear every day. Please visit this Worth Publishers YouTube video on infant speech perception.