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WIREs Cogn Sci
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Physics for infants: characterizing the origins of knowledge about objects, substances, and number

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Adults possess a great deal of knowledge about how objects behave and interact in our every day environment, yet several puzzles remain unsolved regarding how we manage this ubiquitous skill. The notion of intuitive physics has been a central focus of research on cognitive development in infancy. This article focuses on the origins of knowledge about objects, substances, and number concepts in infancy. The article reviews common themes of solidity, continuity, cohesion, and property changes as they have been studied with regard to infants' knowledge about objects and more recently with regard to infants' knowledge about substances. In addition, we review how object and substance knowledge interfaces with number knowledge systems. The evidence supports the view that certain core principles about these domains are present as early as we can test for them and the nature of the underlying representation is best characterized as primitive initial concepts that are elaborated and refined through learning and experience. WIREs Cogn Sci 2012, 3:19–27. doi: 10.1002/wcs.157

Figure 1.

Infants were habituated to a screen that rotated 180° back and forth. Next, a box was placed in the path of the rotating screen. There were two types of test trials. In the expected event, the screen rotated until it came in contact with the box then reversed direction. In the unexpected event, the screen rotated up hiding the box and then continued to pass through the space where the box was located. Infants looked longer at the unexpected compared to the expected events. Adapted from Refs 7 and 8.

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Figure 2.

Infants were habituated to an event where they were shown an empty stage with a barrier wall on the right side. A screen was lowered covering the right side of the stage and the lower portion of the barrier. The experimenter brought out a ball and waved it to call the infant's attention then rolled the ball so that it went behind the screen and came to rest next to the barrier wall. The screen was then raised and looking time at the outcome was recorded. Next, a second barrier wall was introduced to the display. There were two types of test trials. In the expected event, the screen was lowered covering the lower portion of the barriers, the experimenter brought out a ball, waved it to call the infant's attention then rolled the ball so that it went behind the screen and came to rest on the near side of the new barrier wall. The screen was raised and looking time to the outcome was recorded. The unexpected event was identical except that when the screen went up the ball was against the far barrier wall. Infants looked significantly longer at the unexpected compared to the expected outcome. Adapted from Ref 9.

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Figure 3.

Five‐month‐old infants were habituated to displays of tall glass containing either liquid or a perceptually identical solid. In both conditions, the glass was tipped back and forth to demonstrate the motion cues of its contents. (a) During the test trials for solidity, all infants received trials that alternated between a checkered pipe being lowered into a glass. On half the trials, the contents of the glass were liquid and the pipe penetrated the surface of the liquid and came to rest on the bottom of the glass. On the other half of the trials, the contents of the glass were solid and the pipe stopped when it came in contact with the surface of the solid. Looking time was measured to the test displays. Infants habituated to the liquid trials looked longer at the solid test trials, while infants habituated to the solid trials looked longer at the liquid test trials. (b) During test trials for cohesion, all infants received trials where the contents transferred between two glasses and one of the glasses had a grid inside it. On half of the trials, the contents of the glass were liquid and it passed through the grid and collected in the bottom of the glass. On the other half of the trials, the contents of the glass were solid and came to rest on top of the grid inside the glass. Looking time was measured to the test displays. Infants habituated to the liquid trials looked longer at the solid test trials and the opposite pattern was found for infants habituated to the solid trials. Adapted from Refs 19 and 20.

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Figure 4.

Six‐month‐old infants were habituated to displays containing either 8 or 16 dots. At test, all infants received test trials in which they saw both 8‐ and 16‐dot displays, on alternating trials. Looking time was measured to the test displays. Infants habituated to 8 dots looked longer on average at the 16‐dot test displays, while infants habituated to 16 dots showed the opposite looking pattern. Thus, infants in both habituation groups reliably discriminated 8 from 16 dots (a 1:2 ratio). A separate group of infants tested in the same procedure failed to discriminate 8 from 12 dots (a 2:3 ratio). Note that the displays were controlled for nonnumerical cues that tend to covary with number, such as surface area and density, suggesting that infants' performance reflects genuine sensitivity to numerical quantities. Adapted from Ref 24.

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Figure 5.

Bars depict the number of infants choosing the larger or smaller amount. Note that all amounts were hidden in cups during the choice period. (a) 10‐ to 12‐month‐old infants reliably chose two crackers over one in an object condition, but required a 1:4 ratio in order to choose the greater of two quantities of substance. (b) Infants performed at chance with substance quantities differing by a 1:4 ratio when either perimeter or density was removed as a cue to amount. (c) In a sequential version of the task where the quantities differed by a 1:4 ratio, and in which infants only saw one amount at a time before being hidden, 14.5‐month‐old infants reliably chose the greater quantity but 10‐ to 12‐month‐old infants chose randomly. Adapted from Ref 56.

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