Even though babies aren't quite ready to fill out I.Q. tests, researchers still know quite a bit about what is going on in their minds. Babies start to recognize their mothers' faces by one to two months.

At two months or so they become interested in things besides themselves and their mothers — this is the time to get out the toys. (This is a useful development, because it means your baby can be distracted when he is fussy.)

Between the ages of three and four months your baby can understand that three objects are more than two. At around four months she learns to anticipate regular events. For example, she may open her mouth when she sees you getting out your nursing pillow or taking a bottle out of the refrigerator.

At around four months she will also start preferring certain people or certain toys to others. At five months or so she'll learn to follow another person's gaze — if you look up at an airplane, your baby will probably look up, too. Somewhere between six and nine months she'll recognize that a face that she sees in a mirror is her reflection, not another baby, and may spend hours exploring that phenomenon.

At around eight to nine months she'll understand object permanence — that when you leave the room or a toy is hidden out of sight, it continues to exist. (You can test this understanding by hiding a toy under a blanket. Until your baby understands object permanence, she won't bother to look for it, but may cry because it's gone.) By eight or nine months, your baby will be able to set a goal (get a toy), make a plan to carry it out (crawl around the table), and ignore distractions (you calling her in the other direction) while she carries out her plan. Here is a listing of some major intellectual milestones:

INTELLECTUAL MILESTONES