Your Brilliant Baby in Week 25: Crawling & Judging Depth Perception

see larger photo

Baby's Brain in Week 25

It won't be too long before your wiggly baby begins crawling. Crawling is tough stuff for the infant brain: It requires a child to move his left hand and arm forward while moving his right leg and foot forward in a cross-body, synchronized motion. Then Baby must alternate with the right hand and arm and the left leg and foot. (Check it out, here.) Whew!

Before this traditional form of crawling occurs, many babies drag or roll themselves across the floor, all which leads to concerns for the child's safety. Will she fall down the stairs? Off the edge of the sofa?

In a controlled environment, researchers set babies on a glass surface. Just below the surface was a checkered tablecloth which, halfway across the length of the glass, appeared to drop off to about three feet.

If the babies crawled to the edge of the cloth but then stopped at the fake drop-off, it would prove that they had acquired depth perception, the ability to view the world in 3-D—and those babies would have realized the dangers of falling off the "cliff" ahead. If they hadn't acquired depth perception, they would continue to crawl across the glass table, ignoring the appearance of the cliff below.

Typically, on the first few trips across, all infants crawled across the cliff without hesitation. On subsequent trials—even though nothing unpleasant had happened or any variable of the setup had changed—the infants became increasingly reluctant to cross over the visual cliff. We now seem to know that as babies gain experience in crawling, they acquire a wariness of heights. Babies in the research studies eventually learned to stop at the "visual cliff," even when their parents were on the other side of the glass table coaxing them across. ("No way, Mom!")

Remember, much of development is about survival; therefore, as babies begin to crawl, their minds gradually equip them with the ability to notice and fear various edges—whether a stair step inside the home or a ditch outside—that they might encounter in their environment.