A. Research Problem
There once was a man who, for privacy reasons, shall be known as S.B. Blind his entire life, S.B. underwent a relatively new surgery, a common procedure today known as the corneal transplant, to restore his sight. He underwent the surgery and returned finally being able to see after fifty-two years of life. Although unbeknownst to him, his sight was missing something incredibly important: depth perception. S.B. had lived his whole life blind, yet certainly understood the concept that there is depth between objects of varying size. So how could S.B. not understand that and do something as dangerous as climb out of a window?
Depth perception has widely been thought of as innate, for good reason. As the text points out, “you can imagine how difficult and probably impossible, survival of the human species would have been if we could not perceive depth” (Hock, 2015, p. 28). That scenario is easily imaginable, therefore it makes sense that depth perception must be something instinctive, known at birth because if it was not the human species would not have lived long enough to discover and learn depth perception. In the fact of that logic, as if to spite it, babies constantly need some kind of protection against falling off of higher objects. Eleanor Gibson and Richard Walk set out to determine whether or not depth perception was an instinctive skill or if it was something that was acquired over time, while growing up.
B. The Theory
Since depth perception is such an immensely important tool for survival, it can be assumed that such an important skill would be known at birth. Without this tool, any person (or animal in general for that matter) would not be able to determine whether there was some sort of drop, perhaps off a cliff, that could seriously harm if not kill the individual. Therefore its logical to assume such a skill must be inherently known. Despite this, there are a number of every day experiences that can put that entire perspective into question. For example, babies are very prone to falling off objects, especially while developing their motor skills. If such a skill was instinctive, should not the baby be aware that there is a height difference between the ground and whatever object the baby is on? Furthermore, over time babies become less prone to falling over the edge of various objects they are sitting on. The discrepancy between these two propositions allowed Gibson and Walk to test whether or not the ability is instinctive or learned and if it differs between species, taking the position that it was in fact, instinctive.
C. The Method
The visual cliff experiment is rather simple. It is a test that allows researchers to experiment with depth perception without causing any harm to the subjects that are participating in the experiment. The visual cliff was no more complicated than a table with a deep drop on one side and none on the other. A pattern of some sort was placed onto the table, down the side and onto the floor to enable to child to see it better. Finally, it was covered with a thick piece of glass and the child would be placed in the center of the table.
The experiment included “36 infants between the ages of 6 months and 14 months. The mothers of the infants also participated” (Hock, 2015, p. 29). The actual method of this experiment was really simple. The mother simply called to the child from the other end of the table where the child would have to cross the deep end, and the child either went to the mother or did not. Whether or not the child went across the deep end determined if the child had depth perception or not.
D. Findings and Importance
After testing all thirty-six children, they reported their findings. The experiment showed that “nine children in the study refused to move… When the mothers of the other 27 children called to them from the shallow side, all the infants crawled off the board and crossed the glass” (Hock, 2015, p. 30). When asked to go to their mothers on the shallow side, all the babies except nine enthusiastically chose to go to their mothers. Although, “when called from the ‘cliff’ side, most of the children either crawled away from the mother” (Hock, 2015, p. 30). The fact that all of the children crawled to their mother on the shallow side but not the deep side showed that the children had some idea of depth perception. Though it did not prove it was acquired instinctively, as the children were old enough to have learned it on their own.
Thankfully, they had more success with animals, which generally learn to move quite early in life (within the first few days of life, typically). They discovered by experimenting with baby chickens, “at less than 24 hours of age, they never made the mistake of stepping off onto the deep side” (Hock, 2013, p. 31). A similar response was discovered with baby goats, which froze when placed on the deep end but relaxed when put onto the shallow end. This therefore “indicated that the visual sense was in complete control” (Hock, 2013, p. 31). Certain animals, like chicks and kids (baby goats), by a very early age had a complete, instinctive, understanding of depth perception. Rats on the other hand were a completely different story. They showed no like or dislike to either side of the table. Most remarkably though, were the sea turtles. The sea turtles “were ‘smart’ enough to realize they were not in water: 76% of them crawled off into the shallow side, while 24% went ‘over the edge’” (Hock, 2013, p. 32). This was understandable because sea turtles have no real fear of falling, as falling in the open ocean does not happen, thus showing that sea turtles had no evolutionary need for depth perception. Gibson and Walk do point out that “all of their observations were consistent with evolutionary theory. That is, all species of animals, if they are to survive, need to develop the ability to perceive depth by the time they achieve independent movement” (Hock, 2013, p. 32), providing evidence that depth perception is an evolutionary acquired trait, not learned.
The experiment carried great importance. First and foremost, the method of experiment – the visual cliff, has allowed behavioral scientists to experiment with depth perception at great lengths. Additionally, by modifying and applying the visual cliff method, one study showed the concept of a “technical visual cliff” (Hock, 2015, p. 33). This was applied to those with phobias, particularly acrophobia – extreme fear of heights. Studies have shown that therapeutic effects of a “virtual drop… was less threatening for the client, which allowed for more effective therapy to reduce the irrational fear” (Hock, 2015, p. 33). Most importantly, it showed that some traits/characteristics like depth perception are present in some individuals/animals early on, others later, or is not even present at all, suggesting that other behavioral traits may differ between individuals and species.
References
Hock, R. R. (2013). Forty Studies that Changed Psychology: Explorations into the History of Psychological Research (7th edition). New York, NY: Pearson.