Flexibility in Action: Development of Locomotion Under Overhead Barriers

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 (8 girls) and 14 13-month-old (7 girls) walking infants, and a comparative sample of 14 adults (8 women). 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 2 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 quickly (within 4 seconds) 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 more related to age than to walking experience. Thus, development of flexibility likely involves the contributions of multiple domains—motor, perception, and cognition—that facilitate strategy selection and implementation.