Infants' perception of affordances of slopes under high- and low-friction conditions

Abstract

Three experiments investigated whether 14- and 15-month-old infants use information for both friction and slant for prospective control of locomotion down slopes. In Experiment 1, high- and low-friction conditions were interleaved on a range of shallow and steep slopes. In Experiment 2, friction conditions were blocked. In Experiment 3, the low-friction surface was visually distinct from the surrounding high-friction surface. In all three experiments, infants could walk down steeper slopes in the high-friction condition than they could in the low-friction condition. Infants detected affordances for walking down slopes in the high-friction condition, but in the low-friction condition, they attempted impossibly slippery slopes and fell repeatedly. In both friction conditions, when infants paused to explore slopes, they were less likely to attempt slopes beyond their ability. Exploration was elicited by visual information for slant (Experiments 1 and 2) or by a visually distinct surface that marked the change in friction (Experiment 3).

Figure 1

Adjustable sloping walkway used in Experiments 1 and 2. Depending on the friction condition, the entire walkway was covered with a high or low friction surface.

Figure 2

Individual affordance thresholds for Experiments 1 and 2. Each pair of symbols represents high and low friction affordance thresholds for one infant.

Figure 3

Walking ability, locomotor decisions, and exploratory activity normalized to infants’ affordance thresholds for Experiments 1 and 2. (A and E) Proportion of trials on which infants successfully walked down slopes without falling. (B and F) Proportion of trials on which infants attempted to walk down slopes. (C and G) Proportion of trials on which infants touched the slopes. (D and H) Latency to initiate descent. The vertical line at 0° represents infants’ threshold slope for each condition. Negative numbers on the x-axis represent slope groups shallower than threshold, and positive numbers represent slope groups steeper than threshold.

Figure 4

Walking ability, locomotor decisions, and exploratory activity against absolute degree of slope for Experiments 1 and 2. (A and E) Proportion of trials on which infants successfully walked down slopes without falling. (B and F) Proportion of trials on which infants attempted to walk down slopes. (C and G) Proportion of trials on which infants touched the slopes. (D and H) Latency to initiate descent. In each graph, the dashed vertical lines indicate the slope group into which the data were binned for analyses. Ns indicate the number of infants contributing data for each degree of slope in each friction condition; all 16 infants contributed data to each of the binned slope groups for statistical analyses. The Ns are the same for the bottom 3 graphs (B, C, and D; F, G, and H) and thus pictured only once.

Figure 5

Stationary sloped walkway used in Experiment 3. The starting and landing areas of the walkway were always covered with a high friction surface. On low friction trials, the middle portion of the walkway contained a low friction surface.

Figure 6

Walking ability, locomotor decisions, exploratory activity, and gait modifications for Experiment 3. (A) Proportion of trials on which infants attempted to walk down the middle portion of the walkway (Attempts, striped bars) and succeeded in walking without falling (Success, white bars). (B and E) Proportion of trials on which infants touched the middle area of the walkway. (C and F) Time required for infants to reach the middle of the walkway. (D) Attempts to walk over the middle portion of the walkway. For panels A-C, the x-axis represents the two friction conditions; for D-F, the x-axis represents infants’ first, second, and last trials in high friction (black bars) and low friction (white bars) trials.