Researchers have long studied infants' perceptions of safe and risky ground by observing their willingness to cross a visual cliff, a large drop-off covered with a solid glass surface. Now a new study has found that although infants learn to avoid the drop-off while crawling, this knowledge doesn't transfer to walking. This suggests that what infants learn is to perceive the limits of their ability to crawl or walk, not a generalized fear of heights.