In 1960, Eleanor Gibson and Richard Walk conducted an experiment to see whether depth perception is an inborn or a learned skill in humans. They conducted their experiment with a table that had a thick glass surface on half of the table and a solid base on the other half. This created an illusion of a small cliff without the dangers of actually falling. In this experiment, infants ranging from the age of 6 to 14 months were placed on the solid side of the table. The infants mothers were placed on the other side of table and were there to coax the infants to the other side. Of the 30 infants tested, 27 of them crossed the glass surface when called while only 3 refused. Gibson and Walk conducted the same experiment on newborn chickens and goats with astonishing results. When chickens and goats were placed on the solid side, not a single one of them made an error to cross the cliff. The same test was conducted on baby rats whose results fared far worse than the results of the chickens and goats. The rats fared worse because they are nocturnal animals who rely on other senses other than vision to direct them. From this experiment, Gibson and Walk concluded that depth perception was inborn to all animals and humans by the time they achieve independent movement. This is in the case of chickens and goats at birth and for humans at around 6 months of age.
The results of Gibson and Walks experiment are very questionable because their control group did not consist of any socially dependant animals. Infants are socially dependent of their mother for survival and nurturing throughout their childhood. Gibson and Walk should have conducted their control experiment on socially dependant animals such as elephants or cheetahs instead of animals that do not rely heavily on their caretaker. In 1985, Sorce, Emde, Campos, and Klinnert conducted the same visual cliff experiment with human infants and their mothers. This time, the mother was instructed to maintain an expression of fear or happiness on the other side of the cliff. When the mother expressed a happy face, the babies checked the cliff and crossed. When the mother showed an expression of fear, the babies were very reluctant to cross. When the cliff was covered, the babies crossed the table without looking up at their mothers. This study not only proves that facial recognition is an inborn quality of humans but it shows that infants learn depth perception from trial and error through their inborn reliance on their caretaker.