What infants know and what they do: Perceiving possibilities for walking through openings.

What infants decide to do does not necessarily reflect the extent of what they know. In the current study, 17-month-olds were encouraged to walk through openings of varying width under risk of entrapment. Infants erred by squeezing into openings that were too small and became stuck, suggesting that they did not accurately perceive whether they could fit. However, a second penalty condition revealed accurate action selection when errors resulted in falling, indicating that infants are indeed perceptually sensitive to fitting through openings. Furthermore, independent measures of perception were equivalent between the two penalty conditions, suggesting that differences in action selection resulted from different penalties, not lack of perceptual sensitivity.