Cliff or step? Posture-specific learning at the edge of a drop-off

Abstract

Infants require locomotor experience to behave adaptively at a drop-off. However, different experimental paradigms (visual cliff and actual gaps and slopes) have generated conflicting findings regarding what infants learn and the specificity of their learning. An actual, adjustable drop-off apparatus was used to investigate whether learning to distinguish a step from a cliff transfers from crawling to walking. Experienced 12-month-old crawlers (n = 16) refused to crawl over risky drop-offs but novice 12-month-old walkers (n = 17) stepped repeatedly over the edge. Experienced 18-month-old walkers (n = 18) refused to walk over risky drop-offs but descended using alternative methods. These findings suggest that infants do not acquire generalized responses like fear or wariness of heights. Rather, infants learn to perceive affordances for the experienced action.

Figure 1

Apparatuses used to study infants’ behavior at the edge of a drop-off. (A) Visual cliff. (B) Adjustable slope apparatus used in Adolph et al. (2008). The slope angle adjusts from 0° to 50° in 2° increments. (C) Adjustable gap apparatus used in Adolph (2000). The gap width adjusts from 0 to 90 cm in 2-cm increments. (D) Adjustable drop-off apparatus used in the current study. The drop-off height adjusts from 0 to 90 cm in 1-cm increments.

Figure 2

Affordance thresholds for (A) 12-month-old crawlers and walkers in Experiment 1 and (B) 18-month-old walkers in Experiment 2. Each symbol represents one infant, and solid lines represent group means.

Figure 3

Crawling and walking attempts and avoidance. Average proportion of trials in Experiment 1 in which (A) 12-month-old crawlers attempted to crawl and walkers attempted to walk over the drop-off or (B) avoided descent. Average proportion of trials in Experiment 2 in which (C) 18-month-old walkers attempted to walk over the drop-off or (D) avoided descent. Error bars denote standard errors. The dashed line represents infants’ affordance thresholds, and the increments −3, +3, +6, and +9 represent safe and risky drop-offs normalized to threshold. 1 cm and 90 cm represent absolute increments.

Figure 4

Proportion of refusal trials in which (A) 12-month-old crawlers and walkers in Experiment 1 and (B) 18-month-old walkers in Experiment 2 used alternative backing, sitting, or crawling descent methods, or avoided descent.

Figure 5

Relations between posture-specific locomotor experience (days since crawling onset for crawlers, days since walking onset for walkers) and individual differences in error rates (proportion of crawling and walking attempts on risky drop-offs larger than affordance threshold).

Figure 6

Exploratory behavior. In Experiment 1, (A) mean latency for 12-month-old crawlers and walkers to descend (30-s latency indicates avoidance for the duration of the trial) and (B) average proportion of trials in which infants touched the edge with hands or feet or reached into the precipice and retracted their arms. In Experiment 2, (C) mean latency for 18-month-old walkers and (D) average proportion of trials in which they explored by touching. Error bars denote standard errors. The dashed line represents infants’ affordance thresholds, and the increments −3, +3, +6, and +9 represent safe and risky drop-offs normalized to threshold. 1 cm and 90 cm represent absolute increments.