Flexibility in action: Development of locomotion under overhead barriers

Abstract

Behavioral flexibility-the ability to tailor motor actions to changing body-environment relations-is critical for functional movement. Navigating the everyday environment requires the ability to generate a wide repertoire of actions, select the appropriate action for the current situation, and implement it quickly and accurately. We used a new, adjustable barrier paradigm to assess flexibility of motor actions in 20 17-month-old (eight girls, 12 boys) and 14 13-month-old (seven girls, eight boys) walking infants and a comparative sample of 14 adults (eight women, six men). Most participants were White, non-Hispanic, and middle class. Participants navigated under barriers normalized to their standing height (overhead, eye, chest, hip, and knee heights). Decreases in barrier height required lower postures for passage. Every participant altered their initial walking posture according to barrier height for every trial, and all but two 13-month-olds found solutions for passage. Compared to infants, adults displayed a wider variety of strategies (squat-walking, half-kneeling, etc.), found more appropriate solutions based on barrier height (ducked at eye height and low crawled at knee height), and implemented their solutions more quickly (within 4 s) and accurately (without bumping their heads against the barrier). Infants frequently crawled even when the barrier height did not warrant a low posture, displayed multiple postural shifts prior to passage and thus took longer to go, and often bumped their heads. Infants' improvements were related to age and walking experience. Thus, development of flexibility likely involves the contributions of multiple domains-motor, perception, and cognition-that facilitate strategy selection and implementation. (PsycInfo Database Record (c) 2022 APA, all rights reserved).

Figure 1.

Apparatus and participants. (A) Adjustable overhead barrier. Participants walked on an elevated walkway. Between trials the barrier was adjusted to five heights (overhead-, eye-, chest-, hip-, or knee-height). Infants’ caregivers sat at the end of the walkway and encouraged infants to pass under the barrier to retrieve toys, snacks, and hugs. An experimenter followed alongside infants to ensure their safety on the raised walkway. Line drawing is the authors’ original artwork. (B) Standing height in infants and adults. Dashed lines denote group averages. Numbers on graph denote the mean, minimum, and maximum for each group. Barrier height was normalized to each participant’s standing height.(C) Infant age and walking experience. Each symbol represents a single infant (blue for boys, red for girls) and dashed lines denote group averages for age (x-axis) and walking experience (y-axis). Numbers on graph denote the mean, minimum, and maximum for each group. Dark yellow region denotes overlap in walking experience between the 13- and 17-month-olds. Light yellow region denotes 17-month-olds within 1 week of the 13-month-olds.

Figure 2.

Solutions for passing under barriers. (A) Silhouettes show all observed locomotor solutions. Bipedal strategies were walking, ducking, and squat-walking; midway strategies were half-kneeling and hands-feet crawling; crawling strategies were hands-knees crawling, low crawling, and belly crawling; or participants could fail to find a solution for passage. Barrier heights are displayed against the silhouette of walking to illustrate body-scaled heights. Line drawing is the authors’ original artwork. (B) Variety of solutions used by each participant on at least one trial. Colors correspond to the silhouettes in (A). Each row represents a participant. Rows are ordered by the variety of solutions displayed. Empty spaces mean that the strategy was not displayed. Note, the 17-month-old who never walked on overhead barrier trials had 4 months of walking experience and he walked in the warm-up trials. (C) Appropriateness of strategy choice by barrier height. Stacked bars show the average percent of trials for each barrier height by age group.

Figure 3.

Quickness and accuracy of solutions. (A) Average latency across trials at each barrier height for each age group at each barrier height. Error bars denote standard errors. (B) Average number of postural shifts prior to passage for each age group at each barrier height. Error bars denote standard errors. Note, 1 adult ducked prior to squat-walking or hand-feet crawling on 1 trial each at chest- and hip-heights, respectively. And another adult squat-walked prior to hand-knees crawling at hip-height. (C) Head bumps for each age group at each barrier height. Green bars denote no head bumps; red bars denote initial head bumps; yellow bars denote traveling head bumps; and striped bars denote both initial and traveling head bumps.