Fear of heights, which infants typically don’t show until 7 to 9 months of age, is an important part of infant development, since it helps prevent them from harming themselves.
But before infants acquire height wariness, they will fall from couches, tumble over the edges of beds, and, if not strapped in, wiggle out of highchairs. Even after falling, they are likely to keep on doing it.
How, then, does the lifesaving fear of heights develop?
Earlier research suggests that it grows from psychological changes as infants mature. As infants change, so do their mental and emotional abilities to protect themselves from danger, the research concluded.
But more recent experiments by University of California, Berkeley, psychology professor Joseph Campos, San Francisco State University kinesiologist David Anderson and their colleagues arrived at another explanation. The international group of psychologists found that infants develop fear of heights based on visual experiences that result from moving around their environment.
Campos and Anderson’s team believe that a feature of peripheral vision called “visual proprioception” more likely drives the development of height wariness.
Visual proprioception is the visually based perception of self-movement. It involves optic flow data, information about the apparent motion of objects and surfaces seen in the periphery, entering the brain and activating regions linked with the inner ear and various muscles responsible for balance.
Before learning to crawl, infants show very little responsiveness to visual proprioception during moments when they’re in motion, such as when their parents carry them across a room. Contrarily, when they start crawling, visual proprioception from their forward movement sharply increases, teaching them that what they see in their peripheral vision is essential to how they maintain balance.
In situations where infants can’t perceive optic flow data because the motion in the periphery is far away, such as when at a great height, this condition creates a sense of instability and causes a fear of heights to emerge.
In one experiment, the research team used a “moving room” to test the peripheral vision of 9-month-old crawling infants, 13 female and 14 male.
The infants individually were placed in a rectangular enclosure, and the enclosure’s side walls were moved toward the infants. Researchers scored the infants’ peripheral vision based on their ability to perceive, process and show postural changes as they adjusted to the environment moving around them.
Later, the researchers placed this same group of infants on a “visual cliff” to see if the infants would cross it to get to their mothers.
A visual cliff essentially is a Plexiglass-topped platform divided into two sides. The infant is placed on one side, which has a pattern, such as a checkerboard, just below the clear surface, making it look solid.
But on the other side, there’s a gap under the Plexiglass.
The pattern is more than a meter below the clear surface, giving the illusion that crossing over would be like falling off a cliff. The babies are placed on the solid-looking side, and their mothers beckon them to cross over to the side that looks like a drop.
As the researchers predicted, infants with higher scores in the moving room experiment were more likely to avoid the “deep” side of the cliff.
To further test their hypothesis, the researchers trained infants to use small, electric powered “go-carts.” A dozen 7-month-old babies who had not begun to crawl used the carts to gain experience moving from one place to another, providing an opportunity to connect changes in optic flow to physical motion.
The researchers later brought babies that used the carts to the visual cliff, holding them a meter above the “deep” side and lowering them down toward it.
If a baby showed no increased heart rate, the researchers surmised the baby did not show height wariness. However, if the baby’s heart rate accelerated, the researchers surmised the baby had developed a fear of heights.
The team found infants who used the baby go-cart showed increased heart rates. When the researchers tried the visual cliff test with a separate group of babies who hadn’t used the go-carts, they didn’t show the same accelerated rates.
The findings supported the researchers’ hypothesis that connecting visual experiences with self-movement contributes to wariness of heights.
Campos said the experimental work showed a close relationship between balance and the fear of heights. Infants that showed high degrees of postural compensation in the moving room, trying to maintain their balance, showed more of a wariness of heights on the visual cliff than those with lesser degrees.
Likewise, babies showed clear improvement in postural compensation after being trained on the go-carts, and then displayed more wariness of heights than those who hadn’t gone through the same experience.
“So, wariness of heights is more accurately not something that has to do with heights, as much as it does wariness of loss of balance,” he said. “That loss of balance is what leads us to call heights ‘dizzying.’"
Dahl A, Campos JJ, Anderson DI, Uchiyama I, Witherington DC, Ueno M, Poutrain-Lejeune L, Barbu-Roth M.
The epigenesis of wariness of heights
Psychol Sci. 2013 Jul 1;24(7):1361-7. doi: 10.1177/0956797613476047