Infants' reasoning about collision events

The present research investigated young infants' understanding of events in which a moving object collides with a stationary object. In the first set of experiments, 2.5-month-old infants were presented with collision and no-collision events. In the collision events, a cylinder rolled down a ramp and collided with a toy bug that rested at the bottom of the ramp. In the no-collision events, the cylinder again rolled down the ramp but was prevented from contacting the bug. The pattern of results indicated that the infants expected the bug to move when and only when it was hit by the cylinder.The second set of experiments investigated older infants' abilities to reason about variables relevant to collision events. The experiments asked whether infants believed that the size of the moving object in a collision affects the length of the stationary object's displacement. The infants in the experiments were presented with a familiarization event in which a medium cylinder rolled down a ramp and displaced a bug either to the middle (midpoint condition) or to the end (endpoint condition) of a track. Next, the infants were presented with test events in which a small and a large cylinder displaced the bug to the end of the track. The results suggested that 11-, 7.5-, and 6.5-month-old infants, as well as 5.5-month-old female infants, were surprised, in the midpoint condition, to see the small but not the large cylinder displace the bug farther than the medium cylinder had. The infants in the endpoint condition were not surprised by either the small- or the large-cylinder event, suggesting that they realized that neither event was inconsistent with the familiarization event. Together, these results indicated that the infants were engaging in calibration-based reasoning about these events. That is, the infants were using the medium-cylinder event as a calibration point for predicting how far the small and the large cylinders should displace the bug. Follow-up experiments explored changes in infants' expectations and reasoning strategies from 5.5 to 7.5 months of age.The results of the experiments supported two recently proposed hypotheses about knowledge acquisition in infancy: (a) that infants' initial concepts in a domain are all-or-none concepts and that infants gradually come to reason about variables relevant to the domain, and (b) that infants initially use qualitative strategies to reason about these variables and later become able to use quantitative reasoning strategies.U of I OnlyETDs are only available to UIUC Users without author permissio