 Our bodies have an instinctual drive to live right from conception. Without conscious thought to your heartbeats, your diaphragm moves up and down to take in air into your lungs, your immune system constantly checks for infections, your digestive system breaks down food for energy, and your brain takes information about its surroundings to assess dangers in any part of life. The latter of this list is what you would likely call the survival instinct. Is that nagging feeling about a situation, the disgust of rotting food, or even the fear of some animals? One such tool we subconsciously use to protect ourselves is our perception of depth. Is it there from birth or developed over time from experience? Well we all know not to jump off a cliff, even though we haven't experienced it ourselves. We know it's not a great move for our life expectancy. But how to answer the question of when does the depth perception instinct come into being? Well a scientific team would try and find out by trying to get babies to crawl off of a simulated cliff edge. My name is John and welcome to the dark side of science. Our story begins. Our story, like everyone has a beginning, even the ones that involve trying to coax babies to crawl off a simulated cliff. Today our story begins in a place called the Behaviour Farm in the early 1950s, and one of its assistants, the LPHD graduate Eleanor Jack Gibson. The farm was under the control of psychologist Howard Scott Liddell. Liddell had set up the laboratory, modelled on famous behaviourist Ivan Pavlov's Leningrad labs. By the 1950s, the farm was mainly creating experimental neuroses in the animals. On the farm, the subjects read on site were goats, which allowed access to infants for various experiments. Gibson had a burning desire to undertake her own experiments and made use of her time at the farm to study maternal infant interactions. One instant on the farm would create the spark for Gibson's future experimental career. Part of her experiments involved immediately cleaning one of the pair of twin kid goats immediately after birth, with a detergent before the mother had a chance to lick it. This was to see if the maternal bond would be interrupted. Whilst cleaning the kid, its twin appeared. Needing somewhere to place the clean infant, she put it on the top of a camera stand. Interestingly, it stayed neatly keeping its little feet on the stand. This was interesting. It was almost like the animal instinctively new jumping off was a bad idea. Gibson would ultimately quit at the behaviour farm in 1952, when upon returning from a weekend off, finding her goat test subjects, having been given away as Easter gifts. Well, it is at this point that Gibson would meet her research partner, Richard Walk. Walk had arrived at Cornell University as a young professor. The relationship was an odd one for the era, with Walk outranking Gibson by being a professor, but the female research assistant was considerably more experienced in science, and was even 10 years older in age. However, Walk being a professor gave him use of lab space, something Gibson hadn't been able to secure. It would seem the pair would be a good match. They would kick off this working relationship with a study involving rats in environmental differences based experiments, where they would be reared in enhanced or impoverished situations, where the results could be compared to normally raised control subjects. Kind of similar to Harry Harlow's experiments, although a hell of a lot less evil. One of their rat studies involved breeding a cohort of subjects in darkness, to be compared with a control group that had been raised in normal light conditions. To make use of the time-consuming process, Walk and Gibson looked to find another use for their light-deprived victims. This would involve a test involving depth perception. To test if they had depth perception, Walk Gibson and a research assistant, Thomas Tye, built a simulated cliff. This was a pane of glass held up by clamps and rods. To simulate the depth, different colour wallpaper backers were used, with a shallow and deep side separated by a centreboard three inches high. The experiment was the visual cliff alpha version so to speak. Well, much to their surprise, the dark reared rats actually acted just like their control counterparts, preferring to go onto the shallow side of the apparatus. Intriguing, the results would push Walk and Gibson to develop the experiment further, into a more permanent setup. They looked to make the perceived distance of the drop adjustable, and importantly, stronger and robust for a wider range of animals. The duo looked to test on other species of animals, including goats, pigs, chickens, dogs, kittens and monkeys, all of which avoided the deep side. When attempted to be placed on the glass at the deep end, most animals would try and escape, or just refuse to put their feet down on the glass. It looked apparent that depth perception was innate. Well, not quite. When dark reared kittens were placed on the apparatus, they just wandered around, not giving two sods about the deep or shallow side. But the big question was, what would a real human do? Well, it was the late 1950s of course. It was time to find some poo and sick machines to run the experiment on to. The experiment. Prior to the visual cliff, there was not much in the way of depth perception studies in children. This was mainly due to the risks involved with simulating heights, well, at least before Walk and Gibson's method. So the version of the cliff for the baby study was a sheet of plexiglass that covers a cloth with a checkerboard pattern. On one side, the cloth is placed immediately beneath the plexiglass, and thus is the shallow end. And the other side is about 4 feet or 1.2 meters lower, creating the drop. Obviously, there is no risk to the child. There is an illusion of depth, which is accentuated by the cloth pattern. The babies will be placed on the central portion of the apparatus and be encouraged to either the shallow end or cross the void to the deep end by the baby's mother. The key goal was to find if a baby has to develop depth perception or it is born with it. In Walk and Gibson's 1960 paper, they note in their introduction the question of nature versus nurture. Common sense might suggest that the child learns to recognise falling off places by experience, that is by falling and hurting himself. But is experience really the teacher, or is the ability to perceive and avoid the brink part of the child's original endowment? The experiment started off with a pilot beta test. This involved an 18 month old boy. His name is unknown to history, but he crawled to his mother's core on the shallow side. After reaching it, he stood up and shuffled around, when encouraged to cross the deep side, he refused and when placed on the deep end, he showed great stress and anxiety, desperately grabbing at the wooden sides of the apparatus. So Walk and Gibson recruited 36 infants, ranging from the ages of 6 to 14 months. Initially, they were placed on the centre board and observed for a number of minutes. During this time, the mother stood behind a screen. The first two children didn't try to explore their surroundings and because of this lack of results, but the third subject this method was abandoned. But a remainder of the subjects the mother would call their child towards both the cliff and shallow sides successively. Interestingly, when called to the deep side, most of the infants refused and when seeing their mothers on the other side of the chasm showed distress in not being able to reach them. Some even patted the glass over the deep end and even though feeling a solid surface would refuse to cross. Some even moved away to the shallow side, others still just peered into the deep side. Out of the 36 subjects, only three had attempted to go onto the deep side. 27 had moved but only onto the shallow side, with the remainder of the test subjects refusing to move at all or just not following their mother's call and ignoring them. This is quite common in infants as they love to ignore their parents. The mother of the children who had not attempted to venture onto the deep side largely seemed disappointed as they had felt that they had failed the experiment, but the children had shown that they were more dependent on their eyesight than the call of their mother. The experiment showed, at least in most of the test subjects, that depth perception is pretty much there from when we begin to crawl. That was the end of the original study which would be published in 1960, but although arguably answering the question of depth perception and infants, it raised another about maternal trust between child and mother. The three that did venture onto the deep side creates a new dilemma, were they overriding their fear of the fall with their faith in their mother? Well, this would open the door to a whole range of other comparative psychological studies, making the visual cliff a classic form of experiment. One such study was Inter-Meternal Signalling in 1985 by James F. Sors et al, in which the mother was placed across from the chasm and encouraged the infants using various different emotional states, such as happiness, anger and sadness. Happiness unsurprisingly yielded the best results. Another side-quest experiment using the visual cliff on infants was with those who were pre-locomotive, aka pre-crawling, to measure their distress levels when placed on the shallow or deep side. And spoiler alert, in a 1970 experiment by Joseph J. Campos et al, babies became rather distressed in the deep side, hinting at depth perception and thus the fear of heights being innate. That is, from birth. The experiment cemented Walken Gibson into the annals of experimental psychology. But, now it's time to see what you think, was the study ethical? Children weren't harmed, although possibly a bit distressed. The question has to be raised at least for a second about the informed consent, something the children couldn't give. Although nowhere near as bad, it does have some feeling of the baby Albert study or the bobo-doll study. This is a plain difficult production. All videos on the channel are creative commons attribution share alike licensed. Thank you for the videos produced by me, John, in the currently wet and windy corner of southern London UK. I would like to thank my Patreons and YouTube members for your financial support, and also for the rest of you who tune in every week to watch my videos. I have an Instagram, which the link will be in the description, as well as Twitter, where you can check out random pictures on odds and sods. If you're enjoying this outro song, then please feel free to go over to my second channel, made by John, where you can listen to it and watch the video in full. And all that's left to say is miss the music, play us out please, and thank you for watching.