Each time you repeat the sounds your baby makes, you're stimulating his interest and desire to keep communicating with you. It's even more fun when played like a game. But perhaps more important, this imitation exchange helps your infant realize that he can have an effect on his environment - that what he does is important. If you, up to this time, have talked a lot to your baby, he may already recognize certain sounds in your speech. This recognition was indicated by a definite change in their heartbeat rates.
Babies generally show a preference for the female voice.
They would rather listen to a song sung by a woman than to the same song played with musical instruments. They would rather listen to a tape recording of a woman's voice than a man's voice. The higher female pitch may be more interesting. Studies have shown that babies 4-6 months old can discriminate between facial expressions. They look longer at happy faces than at frowning ones.