Why Infants Fall: Development Changes the Causes of Errors as Infants Acquire New Skills

• In Event: Novel Findings and New Methods in Motor Skill Development, Perception, & Learning

Abstract

Errors are indicators of skill mastery level. Commonsense suggests that errors should decrease as infants become more experienced and skilled. Indeed, previous work showed that infant falls—errors in walking—are exceedingly frequent in novice walkers (Adolph et al., 2012). But errors may not decrease as much as commonsense would suggest. In our current dataset of 292 infant walkers (test age = 11.8–20.0 months, walking experience = 2 days to 9.5 months), fall frequency decreased with age and walking experience, rs ≥ -.32, ps ≤ .001, but not as quickly or consistently as expected (Figure 1). On average, falls decreased from 75 times/hour in motion at 12 months to 26 times at 19 months, but the decrease decelerated at older ages.

So, we asked whether the plateaued fall rate reflects developmental stagnation or a previously unrevealed mechanism. To answer this question, we identified the causes of 563 falls in a subset of 161 13-, 15-, and 19-month-olds. As shown in Figure 2A, falls during basic prone activities (crawling; yellow bars) were rare and sporadic across walking experience. Falls during basic upright activities (walking/standing; green bars) were frequent and decreased with walking experience, r(158) = -.45, p < .001. In contrast, falls due to advanced prone activities (e.g., climbing slides/stairs; orange bars) and advanced upright activities (running, spinning, jumping, walking up/down elevations; blue bars) increased with walking experience, rs(158) ≥ .20, p ≤ .01. Thus, the plateau of fall rate in older infants is driven by their spontaneous engagement in new challenging activities.

Further examination of basic upright falls (Figure 2B) showed that these falls were due to a loss of stability (1) in stable conditions (standing or constant-speed walking; purple bars), (2) during spontaneous movements that pull the body off balance (e.g., waving hand, turning head; blue bars), and (3) after unexpected external perturbations (e.g., tripping/slipping; gray bars). Falls caused by loss of balance during stable and spontaneous movements decreased with walking experience, rs ≥ -.37, ps ≤ .001. However, falls caused by unexpected perturbations remained frequent across walking experience, p = .24. Thus, decrease in fall rate is driven by infants’s mastery of basic upright activities.

We extended our analysis of the causes of falls to novice and experienced crawlers to further examine changes in the cause of errors in skill acquisition. Preliminary analyses suggest that basic prone falls decreased with crawling experience, but falls in basic upright postures increased as crawlers started to cruise and walk.

In sum, we found that overall error rate during skill acquisition was a combination of decreasing errors resulting from gradual mastery of current skill and increasing errors due to infants’ spontaneous performance of more advanced skills. Infants’ “curiosity” or “drive” for new challenges creates a developmental spiral of outgrowing old problems, encountering new problems, and thereby incurring new errors. Thus, skills increase in complexity and function without stagnating, and the causes of falls change as a reflection of skill acquisition and development.

Authors

• Danyang Han, New York University
  Presenting Author

• Jaya Rachwani, City University of New York Hunter College
  Non-Presenting Author

• Yueqiao Liu, New York University
  Non-Presenting Author

• Karen E Adolph, New York University
  Non-Presenting Author