THE VISUAL CLIFF AND FEAR OF HEIGHTS
Fear of falling is one of the most fundamental and biologically-adaptive emotions humans and terrestrial animals have. It is a fear that covers the life span, and it is biologically-adaptive, permitting us to avoid injury or death and enabling us to reproduce our genes.
There is a great real-life demonstration of fear of heights in humans at the CN Tower in Toronto. Just before the elevator banks taking one down to street level from the top of the tower, there is a vast expanse of transparent hockey glass that reveals the ground, nearly a thousand feet below. When tourists approach this panel and notice it, they invariably flinch, move away, and show deep respiratory gasps. It is frightening, and nearly universal.
Almost all of the research in this laboratory stems from the discovery that human infants, contrary to widespread opinions expressed in secondary sources, are not afraid of heights. They should be, shouldn’t they, if the fear is so biologically adaptive? But they are not. And we have learned that they are not by using a variant of what the Toronto Tower uses, an apparatus called a visual cliff. This is a table, four feet by six feet in size, covered with thick transparent hockey glass. Under one side (the shallow side), the infant sees red and white checkerboards (babies love checkerboards). On the other side of the table, four feet below the hockey glass, is a similar checkerboard pattern. This is called the deep side. One way of testing infants is to place them on the center of the table, on a strip straddling the deep and shallow sides, and seeing whether they cross to the mother when she calls to the infant to cross to her over the deep side.
Consistent with what mothers typically notice in their own homes, our early research has confirmed experimentally that most infants undergo a period following the acquisition of crawling when they do not avoid heights, typically going over the edge of a bed, changing table, and even the top of a staircase if someone is not there to protect the infant from falling. Then, a few weeks later, the infant who so readily did not avoid heights now behaves as expected and shows fear of falling. The visual cliff apparatus in our lab captures what mothers have reported about a developmental shift from little or no fear of falling to intense avoidance of heights. So, our findings with the visual cliff reveal two important points:
1. There is an unexpected developmental shift enabling infants to become wary of heights and of falling; on the whole, infants are not innately afraid of height, and
2. Something about locomotor experience is playing a role in bringing about this developmental shift.
In the first set of film clips, we document the first of these points. In the clip, we will see three infants:
INFANT ONE: This baby shows the prototypical behavior of an infant with considerable locomotor experience. Notice how the infant approaches the edge of the visual cliff, then backs off, eventually going as far to the mother as the apparatus allows. The child again shows a desire to get to the mother, tests the hardness of the surface of the cliff, but again backs off from crossing. This pattern of behavior continues for the two minute trial, with the infant never crossing the deep side of the cliff to the mother.
INFANT TWO: This infant, who is of exactly the same age as Infant One, crosses the deep side of the cliff to the mother, despite looking down to the deep side of the cliff. The child’s non-avoidance of crossing to the mother is thus not a matter of not being aware that there is a dropoff between the starting point of the test and the place where the mother is calling. Most newly-crawling infants show this pattern of behavior.
INFANT THREE: We have learned a lot about emotions from Infant Three and others like him. This baby, like 20% of experienced crawlers, shows the flexibility of manifesting emotion (in this case, avoiding the dropoff) by showing detour behavior. This baby is exactly the same age as Infants One and Two. Notice how this baby avoids the dropoff by backing away from the center strip of the table, but then notices that he can hitch across to the mother by safely grasping the safety plexiglass barrier that constitutes the near wall of the cliff table, and using the thin wooden strip that supports the hockey glass for footing. This baby accomplishes two goals with one action: He does cross to the mother, but he does not risk fear of falling or significant loss of postural stability.