The Visual Cliff Experiment: When Do Babies Perceive Depth and Fear Heights?
In short
Eleanor Gibson and Richard Walk built a "cliff" that only looks dangerous to test whether infants perceive depth. Nearly all crawling babies refused to cross the apparent drop, even when their mothers called them.
How the experiment worked
The apparatus was a table covered with heavy glass. Under one half, a patterned surface lay directly beneath the glass (the "shallow side"); under the other, the pattern lay on the floor more than a metre below (the "deep side"). Babies were placed on a centre board. 36 crawling infants aged 6–14 months took part. Mothers called the baby from the shallow side and then from the deep side. The researchers also tested young animals: chicks, lambs, kids, rats and kittens.
Results
27 babies crawled onto the shallow side; only three crept onto the deep side when called.
Many babies cried or crawled away from their mother rather than cross, even after patting the glass.
Animals that walk from birth (chicks, kids, lambs) avoided the drop within their first day.
Conclusions and significance for developmental psychology
Gibson and Walk concluded that depth perception is present by the time infants crawl and may have an innate basis. Later work refined the picture. Two-month-olds' heart rate slowed on the deep side — a sign of interest, not fear (Campos et al., 1970). Wariness of drop-offs depends on experience with self-produced locomotion (Adolph, 2000). And one-year-olds decide whether to cross a shallow drop by reading their mother's face: none crossed when she looked afraid, 14 of 19 when she looked happy (Sorce et al., 1985) — the classic demonstration of social referencing.
What it means for parents
Seeing an edge does not mean a baby knows how to stay safe: the skill is relearned with each new way of moving — crawling, then walking. Your reaction and facial expression tell your baby directly whether something is dangerous.
What it means for professionals
The study is a textbook case in the nature–nurture debate and evidence that perception, motor skills and emotion develop together. Social referencing is a useful marker of early social development when assessing children under two.
References
Adolph, K. E. (2000). Specificity of learning: Why infants fall over a veritable cliff. Psychological Science, 11(4), 290–295. https://doi.org/10.1111/1467-9280.00258
Campos, J. J., Langer, A., & Krowitz, A. (1970). Cardiac responses on the visual cliff in prelocomotor human infants. Science, 170(3954), 196–197. https://doi.org/10.1126/science.170.3954.196
Sorce, J. F., Emde, R. N., Campos, J., & Klinnert, M. D. (1985). Maternal emotional signaling: Its effect on the visual cliff behavior of 1-year-olds. Developmental Psychology, 21(1), 195–200. https://doi.org/10.1037/0012-1649.21.1.195