The cost of simplifying complex developmental phenomena: a new perspective on learning to walk

Abstract

Researchers can study complex developmental phenomena with all the inherent noise and complexity or simplify behaviors to hone in on the essential aspects of a phenomenon. We used the development of walking as a model system to compare the costs and benefits of simplifying a complex, noisy behavior. Traditionally, researchers simplify infant walking by recording gait measures as infants take continuous, forward steps along straight paths. Here, we compared the traditional straight-path task with spontaneous walking during 20 minutes of free play in 97 infants (10.75-19.99 months of age). We recorded infants' footfalls on an instrumented floor to calculate gait measures in the straight-path and free-play tasks. In addition, we scored videos for other critical aspects of spontaneous walking-steps per bout, shape of walking path, and step direction. Studying infant walking during free play incurred no cost compared with the straight-path task, but considerable benefits. Straight-path gait was highly correlated with spontaneous gait and both sets of measures improved with walking age, validating use of the straight-path task as an index of development. However, a large proportion of free-play bouts were too short to permit standard gait measures, and most bouts were curved with omnidirectional steps. The high prevalence of these "non-canonical" bouts was constant over development. We propose that a focus on spontaneous walking, the phenomenon we ostensibly wish to explain, yields important insights into the problems infants solve while learning to walk. Other areas of developmental research may also benefit from retaining the complexity of complex phenomena.

Object Interaction and Walking: Integration of Old and New Skills in Infant Development

“…As in Cole, Robinson, and Adolph () and Lee et al. (), the coder identified the duration of each walking bout (time between the first step, when a foot lifted from the floor, and the last step, when a foot rested on the floor for at least 0.5 sec and infants were not shifting weight to another upright step), number of steps per bout, duration of each standing bout (both feet on the floor for at least 0.5 sec, not fully supported by furniture or caregiver, legs extended), and falls while walking (falls while climbing and other activities were excluded).…”

“…Presumably, older infants have more available resources for attention and effort; more experienced walkers have more practice carrying and exploring objects while walking; and more proficient walkers should be less affected by the biomechanical consequences of concurrent object interaction. We measured walking proficiency in a standard gait task: Infants walked several times in a straight path to their caregivers over a pressure‐sensitive mat, and we calculated their walking speed, step length, and step width (Adolph & Robinson, , ; Lee, Cole, Golenia, & Adolph, ). Of course, age, experience, and proficiency are intercorrelated such that older infants are also more experienced and proficient, providing a way to corroborate parents’ reports of walking experience and measures of walking proficiency (Adolph, Vereijken, & Shrout, ).…”

Use it or lose it? Effects of age, experience, and disuse on crawling

“…These low group averages conceal substantial inter‐individual variability; although every group contained participants with no unclassifiable steps, the maximum portion of steps excluded was 39% for one infant, 100% for one of the children while crawling on hands and feet, 33% for one young adult, and 11% for one of the adults with UTS. Thus, although trotting was by far the most common gait observed across ages and postures, both it—and existing periodic gait types more broadly—do not accurately describe all patterns of inter‐limb coordination for all crawlers; see also Lee, Cole, Golenia, and Adolph (2018). …”

“…Skill measured in the straight‐ line paradigm (fast crawling with multiple possible gaits) may not indicate skill in more real‐world challenges such as adapting gait to changing terrain. The straight‐line skill paradigm, after all, bears little resemblance to real‐world locomotion (Adolph et al, 2012; Lee et al, 2018). Locomotor experience is crucial for infants to accurately perceive the limits of their abilities (Adolph, 1997, 2000 ; Kretch & Adolph, 2013), and even adults judging their abilities for otherwise familiar actions show increased accuracy following brief practice in the laboratory (Cole, Chan, Vereijken, & Adolph, 2013; Franchak, van der Zalm, & Adolph, 2010).…”

Behavioral flexibility in learning to sit

“…The current findings argue against this standard-before-flexibility hypothesis. Similarly, recent findings indicate that infants take omnidirectional steps along curved paths from their very first week of walking and that such flexible, situation-specific gait patterns continue unabated across the first 10 months of walking, arguing that flexibility is integral to learning to walk (Lee, Cole, Golenia, & Adolph, in press). …”