Young infants' actions reveal their developing knowledge of support variables: converging evidence for violation-of-expectation findings

Abstract

Violation-of-expectation (VOE) tasks have revealed substantial developments in young infants' knowledge about support events: by 5.5 months, infants expect an object to fall when released against but not on a surface; and by 6.5 months, infants expect an object to fall when released with 15% but not 100% of its bottom on a surface. Here we investigated whether action tasks would reveal the same developmental pattern. Consistent with VOE reports, 5.5- and 6.5-month-old infants were more likely to reach for a toy that rested on as opposed to against a surface; and 6.5- but not 5.5-month-olds were more likely to reach for a toy with 100% as opposed to 15% of its bottom on a surface. Infants at each age thus used their support knowledge to determine whether the toys were likely to be retrievable or to be attached to adjacent surfaces and hence irretrievable. These and control findings extend recent evidence that developmental patterns observed in VOE tasks also hold in action tasks, and as such provide further support for the view that VOE and action tasks tap the same physical knowledge.

Figure 1. Stimuli used in the present research

At the start of the trial, a small squeak toy was brought from behind the screen on the test table and given to the infant to play with; next, the toy was returned behind the screen, which was then removed to reveal two identical copies of the toy. Each infant thus saw three identical copies of the same toy; toys were selected at random from a cast of pink pigs, yellow giraffes, blue hippos, and pink elephants (all made by WinTech). The approximate dimensions of the toys were 5 cm high (9.5 cm high for the giraffes), 3.5 cm wide, and 8 cm long. The screen was 30 cm high and 66 cm wide and, like the table, was covered with blue contact paper. Top: In the type-of-contact condition, the apparatus consisted of a foam board wall 29.5 cm high, 58 cm wide, and 0.7 cm deep. At the bottom of the wall was a platform 5 cm deep; half of the platform was 12.5 cm high and half 3 cm high. The entire apparatus was covered with patterned contact paper. The two toys were attached to the wall by concealed magnets and were positioned 12 cm from the bottom of the wall, with their centers 11 cm on either side of the midline. Thus, one toy rested on the higher half of the platform, and the other lay well above the lower half. On the opposite side of the wall was an identical platform except that its high and low halves were reversed, to counterbalance the position of the retrievable toy across infants. Because the objects were 18.5 cm apart, the infants did not actually have a front view of each object: rather they saw the front and right side of the left object, and the front and left side of the right object, and could thus determine from the available perceptual information that each object was positioned against the wall. As the apparatus was moved closer to the infants, this perceptual information became even more explicit. Bottom: In the amount-of-contact condition, the apparatus consisted of a foam board wall 26 cm high, 61 cm wide, and 0.7 cm deep that stood centered on a thin base 0.7 cm high, 61 cm wide, and 25.5 cm deep. At the bottom of the wall, aligned with the front of the base, were two small identical platforms, each 8 cm high, 11.5 cm wide, and 12.5 cm deep. The entire apparatus was covered with contact paper. One toy stood on each platform, aligned with its front edge; the toy with 100%-support was attached to the center of its platform with double-sided tape, and the toy with 15%-support was attached to its platform by a concealed thin metal strip. One platform was positioned 12.25 cm from the midline and the other 5.25 cm from the midline; the positions of the platforms allowed the two toys to stand with their centers 11 cm on either side of the midline. On the opposite side of the wall were identical platforms except that their relative positions were reversed, to counterbalance the position of the retrievable toy across infants.

Figure 2

Percent reaches to the retrievable toy in each age group and condition. The trial ended as soon as the infant touched a toy; two coders determined which toy the infant had touched. Three infants (one 6.5- and two 5.5-month-olds in the amount-of-contact condition) grazed a toy en route to grasp the other toy fully; the coders agreed that the infants’ intention was to get the toy they grasped fully, so their responses were coded as such.