The Visual Cliff experiment was developed to determine if infants had developed depth perception. The original study is by E.J. Gibson and R.D. Walk. They connect a transparent glass surface to an opaque patterned surface to create the "cliff." The infant is placed on one end of the board and the caregiver then stands on the other side near the glass. If the infant refused to crawl across the transparent surface, they had developed depth perception and perceived the visual cliff. The babies in the video were 6-1/2 to 14 months old and all of them refused to crawl on the glass. Most babies have developed depth perception by 6 to 8 months, and some have even developed by 3 months. It's interesting how at only a couple months they can be enticed to crawl across, but at a certain age they can perceive the situation differently and refuse to cross the glass.