4.3.4 - Baillargeon's explanation of infant abilities
Infants may understand more about objects than their limited actions and speech can reveal. You will examine Baillargeon's physical reasoning system and violation-of-expectation research, where longer looking at an impossible event is treated as evidence of surprise. Evaluation asks whether looking time shows genuine knowledge, reflects perceptual novelty or depends on task design, and how these findings challenge Piaget's timetable.
The core claim
Baillargeon challenged the idea that very young infants know little about the physical world. Piaget associated the emergence of successful hidden-object search with about eight months and interpreted earlier failures as evidence that object permanence was not yet established. He proposed further development during infancy, rather than a complete ability appearing in one instant. Baillargeon's response was methodological: a baby might fail to reach for a hidden toy because reaching, coordinating movement, maintaining attention or staying motivated is difficult, not because the baby thinks the object no longer exists.
Object permanence
Object permanence is the understanding that objects continue to exist when they are hidden or no longer directly sensed.
Object persistence
Object persistence is the principle that objects continue to exist and retain their properties through time and space unless a cause changes them. Being hidden does not by itself make an object disappear, change height or jump to a new location.
Baillargeon's explanation is that infants have some physical expectations earlier than Piaget proposed. Her work investigates persistence, continuity, solidity and developing expectations about support and containment. Different expectations and task features need not emerge at the same time. This is not the same as saying a 5-month-old understands physics like an adult. It means infants may have primitive expectations about physical events earlier than Piaget's search tasks suggested.
Baillargeon's key method was violation of expectation research.
Violation of expectation
Violation of expectation is a method for studying infant cognition in which babies are shown a possible event and an impossible or unexpected event. If they look longer at the unexpected event, this is interpreted as evidence that the event violated an expectation they already had.
The logic is AO1 and research-methods friendly:
| Step | What the researcher does | What it is meant to show |
|---|---|---|
| 1 | Familiarise or habituate the infant to an event. | The infant becomes familiar with the display; reduced looking does not alone identify which physical principle they understand. |
| 2 | Show a possible event and an impossible event. | The two events differ in whether they obey a physical principle. |
| 3 | Measure looking time. | Longer looking at the impossible event is treated as surprise. |
| 4 | Infer the expectation. | The infant may understand the physical principle that has been violated. |
For AQA, the most important contrast is this: Piaget used an action-based measure, whereas Baillargeon used a looking-time measure. Baillargeon therefore argued that infants' failure to search is not decisive evidence that they lack object permanence.
Violation-of-expectation research
A key study for this topic is Baillargeon and Graber's (1987) "Where's the Rabbit?" study. It tested whether 5.5-month-old infants could represent the height of an object when it was hidden behind a screen.
Baillargeon and Graber (1987)
Aim: To investigate whether infants could represent the height of an occluded object and expect it to continue along its path when hidden.
Participants: The first experiment used 24 full-term infants aged from 5 months, 0 days to 6 months, 1 day, with a mean age of 5 months, 13 days.
Procedure: Infants watched a toy rabbit travel along a horizontal track. The middle of the track was hidden by a screen with a window in its upper half.
| Event | What the infant saw | Why it matters |
|---|---|---|
| Possible event | A short rabbit moved behind the screen and did not appear in the window. | The rabbit was too short to be visible through the window, so this was physically possible. |
| Impossible event | A tall rabbit moved behind the screen and still did not appear in the window. | If the tall rabbit continued to exist and kept its height, it should have appeared in the window. |
Findings: In the tall/short condition, infants looked longer at the impossible event than at the possible event. Mean looking times were 33.07 seconds for the impossible event and 25.11 seconds for the possible event. In the second experiment, a pretest showed two separate rabbits. That made it possible to interpret the event as one rabbit disappearing on one side and a different rabbit appearing on the other: neither had to cross the window. Infants in this control did not show the same preference. This matters because the test display could remain unusual while the expected path of a single rabbit changed.
Conclusion: Baillargeon and Graber concluded that the infants represented the rabbit as continuing to exist behind the screen, represented its height, and expected the tall rabbit to appear in the window. This suggests knowledge of object persistence at about 5.5 months, earlier than Piaget's standard estimate for object permanence.
Baillargeon, Spelke and Wasserman's (1985) drawbridge study is another famous VOE example. Five-month-old infants watched a screen rotate like a drawbridge. In the possible event, the screen stopped when it reached a hidden box. In the impossible event, it appeared to rotate through the space occupied by the hidden box. Infants looked longer at the impossible event, which was interpreted as evidence that they expected the hidden box to continue existing and to block the screen's path.
Work through the rabbit inference carefully. First ask what would be visible if one tall rabbit travelled continuously behind the screen: its top should cross the window. Next compare that prediction with the test display: the top never appears. Longer looking is the observed behaviour; representing a persistent, continuously moving rabbit is the inferred explanation. Calling the event “impossible” depends on the one-rabbit assumption, which is why the two-rabbit control is informative.
The physical reasoning system
Baillargeon's broader explanation is that infants are equipped with a physical reasoning system, often shortened to PRS.
Physical reasoning system
The physical reasoning system is a proposed early-developing cognitive system that gives infants basic expectations about the physical world and directs their attention to events that violate those expectations.
The PRS is a nativist idea because it suggests infants are born with a primitive framework for making sense of physical events. Experience still matters. Baillargeon does not claim that infants arrive with a complete rulebook. Instead, infants start with basic principles and then refine them through repeated encounters with objects.
The account combines core principles with learned information about particular event categories. Detecting a violation depends on what the infant has represented: early competence in one type of event does not guarantee the same competence in every other type. The following expectations illustrate its scope; they are not a claim that complete knowledge of all three is present at birth:
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