- Email: [email protected]
Object individuation and event mapping: Infants' use of object speed
633
OBJECT MDMDUATION AND EVENT MAPPING: INFANTS’ USE OF OBJECT SPEED Amy Putthoff and Teresa Wilcox Department of Psychology, Box 19528, University of Texas at Arlington, Arlington, TX 76019 Adults use several types of information to reason about the number of objects present in an occlusion event. One type of information is physical: knowledge about the ways that objects move and interact. Can infants also draw on physical information to individuate objects involved in an occlusion event? Current research suggests that infants are quite successful at using some forms of physical knowledge but may be less successful at using others, For example, in one experiment investigating infants’ use of object speed (Spelke et al., 1995), 4-month-old infants were habituated to an event in which a cylinder disappeared behind one edge of a screen and then immediately reappeared at the other edge. The cylinder continued to move back and forth behind the screen, reappearing immediately each time, until the end of the trial. Following the habituation trials, the screen was removed and infants saw a one- or two-cylinder test event on alternating trials. The infants looked about equally at the two test events, as if they had failed to use the discontinuity in speed to draw a conclusion about the number of objects involved in the habituation event. However, subsequent research suggests that the type of reasoning required to succeed on this kind of task limits performance (Aguiar & Baillargeon, 1997; Wilcox & Baillargeon, in press). To evaluate whether the one- or two-cylinder test event was consistent with the preceding habituation event, the infants had to (a) retrieve their representation of the immediate reappearance habituation event, (b) compare this representation to the test event before them, and (c) determine whether a match existed between the two. Event mapping, as it has been termed, is a difficult task for young infants However, infants are more likely to succeed at event mapping when the initial event is made very simple, by having the objects follow one continuous trajectory rather than emerge multiple times from behind the screen (Wilcox & Baillargeon, in press). The present experiments examined whether infants could demonstrate their ability to use object speed if the initial event were made more simple. In Experiment 1,7.5-month-old infants were assigned to one of two experimental conditions: jmmediate reappearance and pormal reappearance. In the immediate reappearance condition a tower-shaped object moved behind the left edge of a screen and then immediately reappeared at the other edge. Next, the screen was lowered to reveal only the one tower to the right of the screen. Infants in the normal reappearance condition saw the same event, except that the tower reappeared after an appropriate interval. Infants were also tested in two control conditions that were identical to the experimental conditions, except that a second screen stood behind the lowered screen, allowing for the presence of another object. The results indicated that the infants in the experimental immediate reappearance condition looked reliably longer at the one-tower display than the infants in the other three conditions, as if the infants (a) had concluded that one tower was involved in the normal reappearance event and two towers in the immediate reappearance event, (b) had successfully mapped their representation of these two events onto the final display, and hence (c) were surprised to see only one tower after the immediate reappearance event (except when the middle portion of the platform remained occluded). Can infants younger than 7.5 months of age map a discontinuity of speed event? Experiment 2 examined this possibility. 4- and 4.5-month-old infants were tested in the same four conditions described above. The results indicated that the 4.5-month-olds responded like the 7.5-month-olds; the infants in the experimental immediate reappearance condition looked longer at the one-tower display than the infants in the other three conditions. In contrast, the 4-month-old infants in the four conditions looked about equally at the one-tower display, as if they had failed to map the initial occlusion event onto the final event. These fmdings suggest that even when the event is made very simple, 4-month-old infants are unable to map a discontinuity of speed event. We suggest that infants’ success at 4.5 months of age reflects both a change in event mapping abilities and in infants’ ability to use speed of motion for the purpose of object individuation. Further research is planned to investigate infants’ use of other forms of physical knowledge in event mapping tasks.
OBJECT MDMDUATION AND EVENT MAPPING: INFANTS’ USE OF OBJECT SPEED Amy Putthoff and Teresa Wilcox Department of Psychology, Box 19528, University of Texas at Arlington, Arlington, TX 76019 Adults use several types of information to reason about the number of objects present in an occlusion event. One type of information is physical: knowledge about the ways that objects move and interact. Can infants also draw on physical information to individuate objects involved in an occlusion event? Current research suggests that infants are quite successful at using some forms of physical knowledge but may be less successful at using others, For example, in one experiment investigating infants’ use of object speed (Spelke et al., 1995), 4-month-old infants were habituated to an event in which a cylinder disappeared behind one edge of a screen and then immediately reappeared at the other edge. The cylinder continued to move back and forth behind the screen, reappearing immediately each time, until the end of the trial. Following the habituation trials, the screen was removed and infants saw a one- or two-cylinder test event on alternating trials. The infants looked about equally at the two test events, as if they had failed to use the discontinuity in speed to draw a conclusion about the number of objects involved in the habituation event. However, subsequent research suggests that the type of reasoning required to succeed on this kind of task limits performance (Aguiar & Baillargeon, 1997; Wilcox & Baillargeon, in press). To evaluate whether the one- or two-cylinder test event was consistent with the preceding habituation event, the infants had to (a) retrieve their representation of the immediate reappearance habituation event, (b) compare this representation to the test event before them, and (c) determine whether a match existed between the two. Event mapping, as it has been termed, is a difficult task for young infants However, infants are more likely to succeed at event mapping when the initial event is made very simple, by having the objects follow one continuous trajectory rather than emerge multiple times from behind the screen (Wilcox & Baillargeon, in press). The present experiments examined whether infants could demonstrate their ability to use object speed if the initial event were made more simple. In Experiment 1,7.5-month-old infants were assigned to one of two experimental conditions: jmmediate reappearance and pormal reappearance. In the immediate reappearance condition a tower-shaped object moved behind the left edge of a screen and then immediately reappeared at the other edge. Next, the screen was lowered to reveal only the one tower to the right of the screen. Infants in the normal reappearance condition saw the same event, except that the tower reappeared after an appropriate interval. Infants were also tested in two control conditions that were identical to the experimental conditions, except that a second screen stood behind the lowered screen, allowing for the presence of another object. The results indicated that the infants in the experimental immediate reappearance condition looked reliably longer at the one-tower display than the infants in the other three conditions, as if the infants (a) had concluded that one tower was involved in the normal reappearance event and two towers in the immediate reappearance event, (b) had successfully mapped their representation of these two events onto the final display, and hence (c) were surprised to see only one tower after the immediate reappearance event (except when the middle portion of the platform remained occluded). Can infants younger than 7.5 months of age map a discontinuity of speed event? Experiment 2 examined this possibility. 4- and 4.5-month-old infants were tested in the same four conditions described above. The results indicated that the 4.5-month-olds responded like the 7.5-month-olds; the infants in the experimental immediate reappearance condition looked longer at the one-tower display than the infants in the other three conditions. In contrast, the 4-month-old infants in the four conditions looked about equally at the one-tower display, as if they had failed to map the initial occlusion event onto the final event. These fmdings suggest that even when the event is made very simple, 4-month-old infants are unable to map a discontinuity of speed event. We suggest that infants’ success at 4.5 months of age reflects both a change in event mapping abilities and in infants’ ability to use speed of motion for the purpose of object individuation. Further research is planned to investigate infants’ use of other forms of physical knowledge in event mapping tasks.