The baby’s first relationship is usually with mum and dad but he is also able to form attachments with others but it’s the quality of the interaction rather than the length of time.
Babies love to be talked too it doesn’t matter what you say but if talked to in a soft gentle voice they will normally calm down and study your face.
If baby dose not respond to you then check the basics that they are not hungry, need a nappy change or too hot or cold.
It dose not matter if the main carer is the biological mother or not they will always respond to them as long as the primary carer is sensitive to the babies signals and needs for example when the baby smiles, cries or is happy playing or babbling the responds given by the mother establishes the babies early socialization forming the basis for communication between mother and baby.
Babies imitate the gestures and vocal noises that we make this is the way babies learn and develop and this is the main way we can identify when a baby might have hearing problems as this important stage is slowed down or the baby is unaware of the vocal relationship between them and others making social development delayed.
This is what makes feeding, bath time, playing, nappy changing so important in every babies life it’s a time to learn and share experiences as well as having fun.
Never rush this special time with baby as you will unsettle them which will mean a difficult time for you later as they might not sleep or feed as well.
Generally if you are happy and relaxed so will baby which normally means more sleep for you which as every new parent will tell you is the one thing you need.