293 2.5MONTH-OLDS’ REASONING ABOUT OCCLUSION EVENTS Andrea Aguiar & Renee Baillargeon University of Illinois at Urbana-Champaign, 603 E. Daniel St., Champaign, II 61820 Do young infants take into account the presence and location of openings in an occluder to determine whether an object should be visible when passing behind the occluder? A recent experiment examined this question with 2.5- and 3-month-olds. The infants saw events in which a toy mouse moved along a track whose center was occluded by a screen. This screen had a large opening in its upper half (possible event) or its lower half (impossible event). In both events, the mouse disappeared at one end of the screen and reemerged at the other end without appearing in the screen opening. Only the 3-month-olds looked reliably longer at the impossible than at the possible event; the 2.5-month-olds tended to look equally at the two events. The same negative result was obtained in another experiment in which the screen opening in the impossible event was enlarged so that only a narrow strip connected the two sides of the screen . Positive results were obtained, however, when this narrow strip was removed to create two separate rectangular screens. A control condition ruled out the possibility that these positive results merely reflected a perceptual preference for two over one screen. At least two interpretations were possible for the findings obtained with the 2.5month-olds. One was that infants this age are unable to take into account the presence and location of openings in occluders and hence expect an object to remain fully hidden when passing behind any occluder. The second interpretation was that these young infants have difficulty reasoning about occluders that have irregular shapes. The present research was conducted to decide between these two interpretations. The infants saw test events identical to those in the first experiment, except that, in the impossible event, a narrow vertical gap divided the screen in two irregular-shaped halves. The results were similar to those obtained with the two rectangular screens: the infants looked reliably longer at the impossible than at the possible event, suggesting that they expected the mouse to appear between the screens and were surprised when it did not. To provide further evidence for this conclusion, an additional group of 2.Smonth-olds was tested in a control condition identical to the experimental condition with one exception: the two irregular-shaped screens were lowered at the start of each event to reveal two toy mice. The infants in this condition looked equally at the impossible and the possible event, suggesting that they understood how the two mice were used to produce the impossible event. The present findings provide further support for the claim that, when learning about occlusion events, infants initially expect objects to remain fully hidden when passing behind occluders, regardless of the presence and location of openings in the occluders.

2.5-Month-olds' reasoning about occlusion events

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2.5MONTH-OLDS’ REASONING ABOUT OCCLUSION EVENTS

Andrea Aguiar & Renee Baillargeon

University of Illinois at Urbana-Champaign, 603 E. Daniel St., Champaign, II 61820

Do young infants take into account the presence and location of openings in an occluder to determine whether an object should be visible when passing behind the occluder? A recent experiment examined this question with 2.5- and 3-month-olds. The infants saw events in which a toy mouse moved along a track whose center was occluded by a screen. This screen had a large opening in its upper half (possible event) or its lower half (impossible event). In both events, the mouse disappeared at one end of the screen and reemerged at the other end without appearing in the screen opening. Only the 3-month-olds looked reliably longer at the impossible than at the possible event; the 2.5-month-olds tended to look equally at the two events. The same negative result was obtained in another experiment in which the screen opening in the impossible event was enlarged so that only a narrow strip connected the two sides of the screen . Positive results were obtained, however, when this narrow strip was removed to create two separate rectangular screens. A control condition ruled out the possibility that these positive results merely reflected a perceptual preference for two over one screen.

At least two interpretations were possible for the findings obtained with the 2.5month-olds. One was that infants this age are unable to take into account the presence and location of openings in occluders and hence expect an object to remain fully hidden when passing behind any occluder. The second interpretation was that these young infants have difficulty reasoning about occluders that have irregular shapes. The present research was conducted to decide between these two interpretations.

The infants saw test events identical to those in the first experiment, except that, in the impossible event, a narrow vertical gap divided the screen in two irregular-shaped halves. The results were similar to those obtained with the two rectangular screens: the infants looked reliably longer at the impossible than at the possible event, suggesting that they expected the mouse to appear between the screens and were surprised when it did not.

To provide further evidence for this conclusion, an additional group of 2.Smonth-olds was tested in a control condition identical to the experimental condition with one exception: the two irregular-shaped screens were lowered at the start of each event to reveal two toy mice. The infants in this condition looked equally at the impossible and the possible event, suggesting that they understood how the two mice were used to produce the impossible event.

The present findings provide further support for the claim that, when learning about occlusion events, infants initially expect objects to remain fully hidden when passing behind occluders, regardless of the presence and location of openings in the occluders.