Baby hearing is a special topic. There is a different between hearing and actually only absorbing noise and voices. In the beginning, the baby only reacts to tones. It is only later on that it can understand and comprehend words and meanings.
A baby’s ear develops from the time it is born. A baby takes in a lot of information about what happens, but you must remember that everything is new to the baby. That includes the baby hearing itself. This is an exciting stage for your baby, hear noises they cannot place and, later on, identifying voices they know.
Hearing also stimulates brain development by taking the baby to different sounds. Talk therefore a lot with your baby, play music to it and include it in other conversations.
A baby’s hearing is fully developed already at 1-2 month of age. The baby will listen very carefully to the voices and sounds in the beginning, but especially carefully to the voices and bright sound that it recognizes.
When your baby is about 3 months old, it will become more active and responsive to distinguish between language and sound. It can happen that your baby looks straight at you when you talk (regardless if you talk to the baby or to anyone else). Your baby can sometimes answer back, on its own way. The baby expects that you will respond to it and fulfill its immediate needs, but that can be hard as the child has not learned to talk yet.
At about 5 months of age, the baby can hear where the sounds come from and also hear other new sounds coming from any other source. At this age, it listens to the name given to it by the parents.
When a child is 1 year their hearing is fully developed and can now hear normally. It can distinguish between voices (from people he/she knows and people that are strangers) and noises (familiar or unfamiliar).
If you notice that your baby does not turn his head, does not listen to you, does not try to give squeaky responses, than it might have some troubles hearing. Be sure to seek medical advice once you have discovered this, as your baby might have a serious illness or anything else in the ear-tract that prevents it from baby hearing properly.