Physical reasoning in young infants: Seeking explanations for impossible events

Please download to get full document.

View again

of 25
All materials on our website are shared by users. If you have any questions about copyright issues, please report us to resolve them. We are always happy to assist you.
Information Report
Category:

Humor

Published:

Views: 0 | Pages: 25

Extension: PDF | Download: 0

Share
Related documents
Description
Bntrth journal of Developmental Psychology (1W4), 12,9-33 Pnnted in Great Bntain The British Psychological Society 9 Physical reasoning in young infants: Seeking explanations for impossible events
Transcript
Bntrth journal of Developmental Psychology (1W4), 12,9-33 Pnnted in Great Bntain The British Psychological Society 9 Physical reasoning in young infants: Seeking explanations for impossible events RenCe Baillargeon Department of Psychology, University of Illinois, 603 E. Daniel, Champaign, IL 61820, USA There is now considerable evidence that infants are surprised when shown impossible events that violate their beliefs about objects, as indexed by reliably greater looking times at these events than at possible events that are consistent with their beliefs. Do infants also attempt, as older children and adults do, to generate explanations for these impossible events? Data from our laboratory provide intriguing hints that infants, like older children and adults, strive to reconcile what they observe with what they believe. This evidence comes from experiments in which infants were presented with an impossible and a possible event and were found not to show the typical preference for the impossible event. Five examples are presented, involving infants aged 3 to 10 months, and ranging over several facets of infants physical reasoning. It is argued in each case that infants failure to look preferentially at the impossible event stems from their having arrived at some explanation for the event. In some instances, infants explanations appear to be entirely self-produced, as when infants spontaneously posit hidden objects to make sense of otherwise impossible events. In other examples, infants explanations appear to depend on additional clues provided, either deliberately or inadvertently, by the experimental situation. Despite these superficial differences, however, the examples are all related in suggesting that infants, like older children and adults, actively seek explanations for inconsistencies in their world. In recent years, investigators have given increasing attention to the study of infants understanding of the physical world (see Baillargeon, 1993, in press a, b; Spelke, 1988, 1991; Spelke, Breinlinger, Macomber & Jacobson, 1992, for recent reviews). One of the paradigms frequently used by researchers to uncover the nature of infants expectations about objects is the violation-of-expectation paradigm. In a typical experiment, infants see two test events: a possible and an impossible event. The possible event is consistent with the expectation examined in the experiment; the impossible event, in contrast, violates this expectation. The reasoning is that if infants possess the expectation being tested, they will be surprised by the impossible but not the possible event. Because infants surprise at an event typically manifests itself by prolonged attention to the event, it is assumed that, if infants are surprised by the impossible event, they will look reliably longer at it than at the possible event. With the help of this methodology, investigators have been able to demonstrate considerable physical knowledge on the part of young infants. For example, we now know that young infants understand that objects continue to exist when out of sight (e.g.. Requests for reprints. 10 Renie Baillargeon Baillargeon, 1986, 1987a,b, 1991; Baillargeon & DeVos, 1991; Baillargeon & Graber, 1987; Baillargeon, Graber, DeVos & Black, 1990; Baillargeon, Spelke & Wasserman, 1985; Spelke & Kestenbaum, 1986; Spelke et al., 1992), that objects cannot occupy the same space as other objects (e.g. Baillargeon, l986,1987a,b, 1991; Baillargeon & DeVos, 1991; Baillargeon et al., 1985, 1990; Spelke et al., 1992), that objects move along spatially continuous paths (e.g. Baillargeon, 1986; Baillargeon & DeVos, 1991; Baillargeon & Graber, 1987; Spelke et al., 1992), and that objects cannot remain stable without support (e.g. Baillargeon & Hanko-Summers, 1990; Baillargeon, Needham & DeVos (1992); Needham & Baillargeon, 1993, 1994; Spelke, Jacobson, Keller & Sebba, 1993; Spelke, Simmons, Breinlinger, Jacobson & Macomber, 1993). To illustrate the violation-ofexpectation paradigm, I will describe an experiment that provided evidence for the first two of these claims, that is, evidence that young infants appreciate both the permanence and the impenetrability of objects. In this experiment (Baillargeon et al., 1990), 5.5-month-old infants were shown the possible and the impossible events depicted in the upper panel of Fig. 1. At the start of the possible event, the infants saw two covers placed side by side: on the left was a clear plastic cover and on the right was a cage; a toy bear was visible inside the cage. After a few seconds, a screen was raised to hide the two covers from view. Next, a gloved hand reached behind the screen s right edge twice in succession; on the first reach, the hand reappeared with the cage, and on the second reach, with the bear. The impossible event was identical to the possible event except that the bear was under the clear cover at the start of the event and thus should still have been inaccessible to the hand after the cage was removed. A second group of 5.5-month-old infants was tested in a control condition (see Fig. 1, lower panel) that was identical to the experimental condition except that the clear cover was replaced by a clear, shallow container. The bear s head and upper body protruded above the container s rim. In this condition, the bear was always accessible to the hand after the cage was removed. The infants in the experimental condition looked reliably longer at the impossible event than at the possible event, whereas the infants in the control condition looked about equally at the two test events they were shown. Together, these results indicated that the infants (a) believed that the bear, the cage and the cover or container continued to exist, in their same locations, behind the screen; (b) understood that the hand and the bear could not move through the space occupied by the clear cover; and hence (c) were surprised in the impossible event to see the hand reappear from behind the screen holding the bear. The results of this experiment thus indicated that by 5.5 months of age infants already share at least two of adults beliefs about objects, namely, that objects continue to exist when out of sight and that objects cannot move through the space occupied by other objects. Do infants seek explanations for impossible events? Chandler & Lalonde (1994) presented 3- and 4-year-old children with an impossible event in which a screen appeared to rotate through the space occupied by a wooden block. The authors reported that their subjects reacted with marked surprise when Physical reasoning in young infants 11 c m.- 0 12 Renke Baillargeon shown this event, as evidenced by bugged eyes, beady stares, theatrical double takes, audible gasps and giggles (p. 89). The children s responses were not limited to these surprise reactions, however; the authors indicated that virtually all of the children bolted from their seats to explore the apparatus, when no longer prevented from doing so, and eventually discovered the trap door mechanism (p. 89). The evidence reviewed in the previous section suggests that infants are surprised when shown events that violate their beliefs about objects. But do infants also attempt to generate explanations for these events? Unlike older subjects, such as those of Chandler & Lalonde, infants are typically unable to search for answers by exploring the apparatuses before them. Is there other evidence that could be taken to suggest that infants seek explanations for impossible events? Data from our laboratory provide intriguing hints that, like older children and adults, infants strive to reconcile what they observe with what they believe. This evidence comes from experiments in which infants were presented with an impossible and a possible event and were found not to show the typical preference for the impossible over the possible eveqt. In each case it will be argued that infants failure to look preferentially at the impossible event stemmed from their being able to generate an explanation for the event. Children and adults typically do not show surprise at events when conscious of how they were contrived; for example, it is doubtful that the subjects of Chandler & Lalonde would have been surprised to see the screen rotate through the block had they known, or immediately guessed, that the apparatus contained a trapdoor. In each of the examples below, infants atypical response to the impossible event will similarly be ascribed to their having arrived at some explanation for the event. In the next section, I present three examples of situations in which infants appeared to spontaneously produce explanations for events. In the following section, I discuss two examples of situations in which infants, though unable to generate explanations on their own, readily did so when provided (either deliberately or inadvertently) with additional clues. Together, the five examples involve infants aged 3 to 10 months and range over multiple facets of infants physical reasoning. The examples further differ in that in some instances infants ability to generate explanations for the events was explicitly anticipated in the design of the experiments, whereas in other instances this ability was entirely unexpected. Despite these differences, however, the examples are all related in suggesting that infants, like older children and adults, actively seek explanations for inconsistences in their world. Evidence that infants can spontaneously produce explanations for events Example 1: Positing a bidden doll The first example comes from experiments that examined 10-month-old infants ability to represent the existence and number of objects hidden behind a screen (Baillargeon, Miller & Constantino, 1994). The infants saw the possible and the impossible events depicted in the left panel of Fig. 2. At the start of each event, a screen was raised to hide the empty centre section of the apparatus. Next, a gloved hand entered the apparatus twice in succession, each time carrying a small Ernie doll which it deposited behind the screen. The screen was then lowered to reveal a row of two dolls in the possible event, and three dolls in the impossible event (an experimenter introduced a third doll surreptitiously through a hidden door in the back wall of the apparatus). The infants in another (screen- Screen-down Condition Screen-up Condition m Possible Event,w m rn Figure 2. Schematic drawing of the test events used in Baillargeon et af. (1994). 7 E 0 3.r. 3 m 3' % E 3 Do.r. s 3 2 L W 14 Renie Baillargeon up) condition saw the same test events as the infants in the first (screen-down) condition, with one exception: the events began with the screen already up, so that the infants did not see that the area behind the screen was empty (see Fig. 2, right panel). We reasoned that if the infants in the screen-down condition (a) believed that each doll continued to exist after it was deposited behind the screen and (b) realized that the addition of one doll and then another doll behind the screen resulted in an array of two dolls, then they should be surprised in the impossible event when the screen was lowered to reveal three dolls; the infants should therefore look reliably longer at the impossible event than at the possible event. We were less certain, however, what to expect from the infants in the screen-up condition. On the one hand, their performance might be identical to that of the infants in the screen-down condition. On the other hand, it was conceivable that the infants in the screen-up condition might conclude, upon seeing the array of three dolls, that one of the dolls must have already been present behind the screen at the start of the event (though incorrect, this explanation was nevertheless plausible, given the nature of the events). In the latter case, the infants should look equally at the impossible and the possible events, because neither event would seem surprising. The infants in the screen-down condition looked reliably longer at the impossible than at the possible event, whereas the infants in the screen-up condition tended to look equally at the two events. These results indicated that the infants in the screen-down condition (a) understood that depositing one doll and then another doll behind the screen should produce a set of two dolls and hence (b) were surprised in the impossible event when the screen was lowered to reveal three dolls. Furthermore, although the infants in the screen-up condition also appreciated that placing one and then another doll behind the screen should have resulted in an array of two dolls, these infants (a) concluded that one additional doll must have been present behind the screen at the start of the impossible event and hence (b) showed little surprise at this event. To reiterate, what is being argued is that, upon seeing the impossible event, the infants in the screen-up condition readily constructed an explanation for this event: they assumed that one doll already stood behind the screen at the start of the event. Only the infants in the screen-down condition, who possessed information contradicting this explanation and thus were unlikely to generate it, showed reliable surprise at the impossible event. The findings of this experiment (which were replicated in additional experiments: Baillargeon et al., 1994) provide evidence that infants, like adults, attempt to reconcile what they observe with what they believe. By assuming that a doll already stood behind the screen at the start of the event, the infants in the screen-up condition were able to transform an event that would otherwise have violated their beliefs about objects into an event entirely consistent with their beliefs. Example 2: Positing a bidden rabbit The second example to be described in this section involves experiments that examined 5.5-month-old infants ability to represent the existence, height and trajectory of hidden objects (Baillargeon & Graber, 1987). In one experiment, the infants were familiarized with a toy rabbit that slid back and forth along a horizontal track whose centre was occluded by a screen; the rabbit disappeared at one edge of the screen and reappeared, Physical reasoning in young infants 15 after an appropriate interval, at other edge (see Fig. 3). On alternate trials, the infants saw a short or a tall rabbit slide along the track. Following familiarization, the midsection of the screen s upper half was removed, creating a large window. The infants then saw a possible and an impossible test event. In the possible event, the short rabbit moved back and forth along the track; this rabbit was shorter than the window s lower edge and so did not appear in the window when passing behind the screen. In the impossible event, the tall rabbit moved along the track; this rabbit was taller than the window s lower edge and hence should have appeared in the window but did not in fact do so. To produce this event, as well as the other test and familiarization events, two identical rabbits were used: one rabbit moved from the left end of the track to the left edge of the screen and stopped just inside this edge; another, identical rabbit then emerged from the right edge of the screen and travelled to the right end of the track. The infants tended to look equally at the short- and the tall-rabbit familiarization events but looked reliably longer at the impossible test event than at the possible test event. These results indicated that the infants (a) believed that each rabbit continued to exist behind the screen; (b) realized that each rabbit retained its height behind the screen; (c) assumed that each rabbit pursued its trajectory behind the screen; and hence (d) expected the tall rabbit to appear in the screen window and were surprised that it did not. The results of the experiment also indicated that the infants were impervious to the auditory clues that signaled how the familiarization and test events were produced. Whereas a distinct metallic noise could be heard during the visible portions of the tall or the short rabbit s trajectory, on either side of the screen, no noise was heard after each rabbit disappeared behind the screen. To naive adults who watched the events, the absence of noise during the occluded portion of each rabbit s trajectory provided a powerful hint that two separate rabbits were involved in the events, one travelling to the left and the other to the right of the screen. The fact that the 5.5-month-old infants in the experiment appeared unaware of these auditory clues was not unexpected, however, given prior reports that young infants do not make use of available sound clues to track or locate occluded objects (e.g. Meicler & Gratch, 1980; Nelson, 1971; Piaget, 1954). Although the infants in the experiment were unable to infer that two distinct rabbits were used to produce the impossible event, the results of another, unpublished experiment suggest that, under some conditions, 5.5-month-old infants can spontaneously generate such an explanation. The infants in this experiment (see Fig. 4) saw the short-rabbit familiarization event used in the first experiment. Next, the infants watched a possible and an impossible test event. The possible event was the same as that shown to the infants in the first experiment. The impossible event was identical to the possible event with one exception: the window was at the bottom rather than at the top of the screen. In this event, the short rabbit should have appeared in the window when passing behind the screen; it did not, however, do so. As before, two identical rabbits were used to produce the familiarization and test events. For details of apparatus, events and procedure, the reader is referred to Baillargeon & Graber (1987, Expt 1). Subjects in the experiment were 12 infants ranging in age from 4 months 29 days to 6 months 1 day (M = 5 months 10 days). Three additional infants were eliminated, two because of fussiness and one because of drowsiness. The infants saw the short-rabbit familiarization event on four successive trials; they then watched the possible and the impossible test event on alternate trials until they had completed four pairs of test trials (order of presentation of the two test events was counterbalanced across subjects). Three infants completed only six test trials because of fussiness, but were still included in the data analyses. 16 Renee Baillargeon Given the results of the tall/short-rabbit experiment, it is likely that the infants in the upper/lower-window experiment perceived the short-rabbit familiarization event in terms of a single short rabbit moving back and forth along the track. How did the infants perceive the test events? It can be seen in Fig. 5 that, unlike the infants in the tall/short-rabbit experiment, the infants in the upperaower-window experiment tended to look equally at the impossible and the possible events2 We were initially puzzled by this finding: how could the infants in the tall/short-rabbit experiment be surprised that the upper portion (7.5 cm) of the tall rabbit failed to appear in the screen window, and the infants in the upper/lower-window experiment not be surprised that the whole of the short rabbit (15.5 cm) failed to appear in the window? Upon reflection, we came to the hypothesis that, like the 10-month-old infants discussed earlier, the 5.5-month-old infants in the second experiment did not show surprise at the impossible event because they were able to generate an explanation for this event. Specifically, they realized that the short rabbit did not appear in the screen window because it did not in fact travel the distance behind the screen; instead, two identical short rabbits were involved in the production of the event, one travelling to the left and the other to the right of the screen. It might be objected that other, less interesting hypotheses could be advanced for the r
Recommended
View more...
We Need Your Support
Thank you for visiting our website and your interest in our free products and services. We are nonprofit website to share and download documents. To the running of this website, we need your help to support us.

Thanks to everyone for your continued support.

No, Thanks
SAVE OUR EARTH

We need your sign to support Project to invent "SMART AND CONTROLLABLE REFLECTIVE BALLOONS" to cover the Sun and Save Our Earth.

More details...

Sign Now!

We are very appreciated for your Prompt Action!

x