The experiment being referred to was devised at Cornell University by Eleanor Gibson and Richard Walk (1960). The objective was to see if depth perception was an innate ability we had from birth, or something we learned as we matured.
In the test, Gibson and Walk placed infants ranging from 6-14 months on a "visual cliff" - a long glass table about 1 meter high, with an apparent drop off. Gibson and Walk then had the babies' mothers coax them to crawl out onto the glass. In the experiment, most infants refused to do so, indicating that they could perceive depth.
One explanation could be that by crawling age infants had learned how to perceive depth. However, newborn animals with very little visual experience, including young kittens, a day-old goat, and newly hatched chicks, respond similarly. (Myers, 2002) In addition, tests have shown that during the first month of life human infants turn away from objects that are on a direct collision course with them, but not from objects that will not hit them (Ball and Tronick, 1971).
Depth Perception is accomplished in the human body by a combination of binocular cues and monocular cues. It is hypothesized that biological maturation predisposes our wariness of heights, and that experience then amplifies it. As was shown in a video presentation of this experiment, the older a child was, the more likely the child would respond negatively to the experiment. In 1992, a group of researchers determined that when infants' movement is enhanced by a walker, they become even more wary of heights (Campos and others, 1992).
So, in conclusion, babies very well may crawl off cliffs. They are babies after all. Our biological predisposition will usually be enough to prevent them from doing so, but not it all cases. So just like kids on the internet, or around the kitchen, or a busy street, keep an eye on your kids if you want them to stay safe.
References:
- Myers, David G. (2002) Sensation and Perception Exploring Psychology Michigan: Worth Publishers (pp.164-165)
- Gibson, E.J. and Walk, R.D. (1960, April). The "visual cliff." Scientific American, pp. 64-71
- Ball, W. and Tronick, E. (1971) Infant Responses to impending collision: Optical and real. Science, 171, 818-820.
- Campos, J.J., Bertenthal, B.I. and Kermoian, R. (1992). Early experience and emotional development: The emergence of wariness and heights. Psychological Science, 3, 61-64