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Two experiments investigated whether infants would look longer at a rotating "drawbridge" that appeared to violate physical laws because they knew that it was causally impossible, as claimed by R. Baillargeon, E. S. Spelke, and S. Wasserman (1985) and R. Baillargeon (1987a). Using a habituation paradigm, they reported that infants looked longer at a display that appeared impossible (rotated 180 degrees while an obstructing box was behind it) than at one that appeared possible (rotated only 112 degrees, appearing to stop at the box). Experiment 1 eliminated habituation to 180 degree screen rotations. Still, infants looked longer at the 180 degree impossible rotations. Critically, however, infants also looked longer at possible 180 degree rotations in Experiment 2, in which no obstruction was present. Moreover, no difference in effect size was found between the 2 experiments. These findings indicate that infants' longer looking at 180 degree rotations is due to simple perceptual preference for more motion. They question R. Baillargeon's (1987a) claim that it is due to infants' representational reasoning about physically impossible object permanence events.

Three experiments (N = 68), using Wynn's procedure, tested 5-month-old infants' looking time reactions to correct and incorrect results of simple addition and subtraction transformations. The aim was to investigate both the robustness and the parameters of infants' arithmetic competence. Experiments 1 and 2 (N = 44) were replications of Wynn's first two experiments in which infants were shown addition (1 + 1 = 1 or 2) and subtraction (2 - 1 = 1 or 2) requiring imprecise calculation. Experiment 3 (N = 24) was a subtraction counterpart (3 - 1 = 1 or 2) to Wynn's third experiment requiring precise calculation of addition (1 + 1 = 2 or 3). Unlike Wynn, we found no systematic evidence of either imprecise or precise adding and subtracting in young infants. Our results, together with the mix of both positive and negative findings from other studies of infant arithmetic, suggest that infants' reactions to displays of adding and subtracting are variable and, therefore, that infants' numerical competencies are not robust. This conclusion is consistent with previous findings indicating that simple adding and subtracting develops gradually and continuously throughout infancy and early childhood.

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