An experimental group is the group in an experiment that receives the variable being tested. One variable is tested at a time. The experimental group is compared to a control group, which does not receive the test variable. In this way, experimental groups are used to find answers in an experiment.
1 At around 9 months of age, babies begin to pull themselves up to a standing position. 2  By 10 months of age, a baby should be able to grasp objects with thumb and forefinger.
Your infant prefers high-frequency tones like the female voice, probably because she can hear them better. Maybe that's why it's natural for adults to adopt a high-pitched singsong voice (also known as motherese) when talking to babies. By 4 to 6 months your baby should start to repeat recognizable sounds and babble.