John Franchak and Karen Adolph at New York University exposes the limits of this approach, demonstrating that how babies choose to behave isn't based only on their perceptual abilities but also on their assessment of risk.
Thirty-two 17-month-old infants were allocated to one of two conditions - they either had to judge whether they could fit through a narrow gap (of varying widths) between two surfaces, or they had to judge whether they could fit though a narrow gap (of varying widths) between the edge of a table and a wall. Both conditions took place atop a table but the risk in the first case was getting stuck, whereas the risk in the second case was falling off the edge.
The toddlers in the first, "entrapment" condition frequently misjudged the situation and found themselves stuck on over 80 per cent of trials (this error rate showed no signs of diminishing over time). By contrast, toddlers in the "falling condition" were shrewder judges and only fell off on just 21 per cent of trials (don't worry, no babies were hurt in this research). This was the case even though one might imagine that the gap between two wall-like surfaces was easier to judge, from a perceptual point of view, than a gap between a wall and a drop, and despite the fact that infants in both conditions exhibited similar approach behaviours - lining their bodies up in advance and feeling the gaps with their hands.
Franchak and Adolph point out that if developmental psychologists relied on the "entrapment" condition, they would wrongly conclude that infants of this age have yet to develop the sensory and motor sophistication to judge gap size in relation to their own body size. In fact the results from the "falling" condition show that toddlers are capable of judging the relative size of a gap versus their own body. The discrepancy in performance between the two conditions is presumably because babies aren't that bothered about the risk of getting stuck - so they're fairly reckless about trying to squeeze through a too-small gap - but they are bothered about the risk of falling, so they take their size estimations along precipices far more seriously.
As an aside, the infants' histories of getting stuck or not in real life (for example, the researchers noted that one boy had previously managed to get his head stuck in a training potty) bore no relation to their performance in the task.
The researchers said their findings had theoretical implications - challenging previous assumptions made by other psychologists that the tendency for infants to get stuck in gaps meant they had poor body knowledge. The new results also have practical implications. "Falling and entrapment are two of the leading causes of accidental injury in infants," the researchers said. "The results suggest that even though experienced walking infants can perceive risks of falling and entrapment accurately, they may discount the potential danger of entrapment. Their willingness to squeeze themselves into possibly small openings may contribute to the prevalence of entrapment injuries."
Franchak, J., and Adolph, K. (2012). What Infants Know and What They Do: Perceiving Possibilities for Walking Through Openings. Developmental Psychology DOI: 10.1037/a0027530
Post written by Christian Jarrett for the BPS Research Digest.