You may be familiar with experiments that show that infants will not willingly crawl over cliffs. If they get to a drop-off edge, they usually will not proceed any further. This has been interpreted to mean that babies have a natural fear of heights. According to Kari Kretch and Karen Adolph of New York University, this is the wrong interpretation. Instead, infants simply become more adept at gauging their physical limits.
Many of the earlier avoidance studies have involved watching whether babies will crawl across a virtual cliff, generally a sheet of glass or plexiglass. You can see an example of such an experiment below:
The obvious drawback is that the drop-off is only virtual. Babies learn very quickly that they won’t actually fall if they move onto the glass. This makes it difficult to score their innate tendencies. To avoid this problem, infants were placed near actual slopes and drop-offs, with spotters available to catch them before they fell. The researchers compared novice and experienced crawlers with novice and experienced walkers.
The biggest predictor of whether an infant would attempt to cross a drop-off was how long he’d been using that mode of travel (what the authors refer to as ‘posture-specific locomotor experience’). Babies with less than forty days of experience with either crawling or walking would move over the edge. After having successfully crawled or walked for ninety days, they rarely needed to be caught at the cliff’s edge. In other words, infants who had learned to avoid cliff edges while crawling had to relearn to avoid them once they started walking. They neither gain nor retain a fear of heights.
As the authors state:
Crawling experience taught infants to perceive affordances for crawling, and walking experience taught infants to perceive affordances for walking.