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INFANTS’ USE OF FEATURAL INFORMATION IN REASONING ABOUT OBJECT IDENTITY: RECONCILING CONTRADICTORY RESULTS

Teresa Wilcox Department of Psychology, Box 19528, University of Texas, Arlington, TX 76019

Renee Baillargeon University of Illinois, Champaign-Urbana

Can young infants use featural information to reason about the identity of objects that move in and out of view? Recent research (Wilcox & Baillargeon, 1995; Xu & Carey, in press) indicates that the answer to this question depends on the specific paradigm used: whereas experiments conducted with the size comoarison paradigm have yielded positive results in infants as young as 7.5 months of age, experiments carried out with the obiect maopinq paradigm have produced positive results only in infants aged 11.5 months and older.

In one experiment that used the size comparison paradigm (Wilcox & Baillargeon, 19951, 7.5-month-old infants watched a ball disappear behind one edge of a screen; after a brief interval, the same ball (ball-ball event) or a box (ball-box event) appeared at the other edge. The screen was too narrow to hide the ball and box simultaneously. The infants looked reliably longer at the ball- box than ball-ball event. These and control data indicated that the infants (a) used the featural information to conclude that the ball-ball event involved one object and the ball-box event involved two objects; lb) judged that the screen was wide enough to hide the ball but not the ball and box; and hence (13 were surprised in the ball-box event that the objects could be out of view at the same time.

These findings contrast with those of a similar experiment conducted with the object mapping paradigm (Wilcox & Baillargeon, 1995). Infants 9.5 and 11.5 months of age saw events similar to those described above except that the screen was now wide enough to hide both the ball and the box simultaneously. After several repetitions of the ball-ball or ball-box event, the screen was lowered to reveal a stationary array containing one ball. The 11.5-month-old infants looked reliably longer at the final array after seeing the ball-box as opposed to ball-ball event. The younger infants looked equally at the final array regardless of the event seen initially, as though they were unable to judge whether the final array mapped onto the object(s) seen in the preceding ball-ball and ball-box event.

How can we explain the discrepancy between these two sets of findings? The hypothesis examined in the present research was that the multiole emergences of the ball and box on either side of the screen in the object mapping task might have made it difficult for the younger infants to reason about the identity of the objects. (Multiple emergences can have no detrimental effects in size comparison tasks because infants can judge during each event whether the screen is wide enough to hide the objects.)

To examine this hypothesis, 8.5- to 9.5-month-old infants were tested with simplified box- ball and ball-ball events involving single, as opposed to multiple, presentations of the objects on either side of the screen. In the box-ball event, a box disappeared behind the left edge of a screen; after a brief interval, a ball appeared at the right edge and the screen was immediatedly lowered to reveal an empty area behind the screen (i.e., only the ball was present to the right of the screen). The ball-ball event was similar except that the ball appeared on both sides of the screen. The infants looked reliably longer at the final array after having seen the box-ball than ball-ball event. These and control data indicated that the infants (a) realized that two distinct objects were involved in the box-ball event and hence (b) expected the box to be revealed when the screen was lowered and were surprised when it was not.

These results provide converging evidence that young infants can use featural information to reason about object identity. In addition, they suggest that multiple emergences of objects in an occlusion event may interfere with infants’ ability to map information from a moving to a stationary display. We speculate that this difficulty stems from the way that the objects are represented in the moving display.