The development of adaptation

The ability to adapt to change is a critical component of motor skill because we must constantly cope with multiple sources of variability. Two sources of variability are the environment and the body. This dissertation focuses on two studies in which aspects of the environment and of body dimensions were varied. A critical aspect of perception-action coupling is the ability to modify ongoing actions in accordance with variations in the environment. In chapter one, infants' ability to modify their gait patterns to descend shallow and steep slopes was examined at three nested time scales. Across sessions, a microgenetic training design showed rapid improvements in infants receiving concentrated practice on slopes and in control infants who were tested only at the beginning and end of the study. Within sessions, analyses showed that infants used a "braking strategy" to curb increases in walking speed across increasingly steeper slopes. Within trials, comparisons of infants' gait modifications before stepping over the brink of the slopes showed that the braking strategy was planned prospectively. Findings illustrate how observing change in action provides important insights into the process of skill acquisition. Chapter two examined effects of developmental factors on the time course, variability, and variety of patterns used in adapting to change. Infants and adults were presented with a novel challenge—walking with uneven leg lengths. A platform affixed to the bottom of one shoe created leg length asymmetry. Participants walked in four conditions; with even leg lengths, uneven leg lengths with the platform, uneven leg lengths after extended practice, and even leg lengths after the platform was removed. Both infants and adults adapted rapidly to the addition of the platform, but only adults showed stable, consistent responses. They showed a uniform response with taking a shorter step with the short leg and a slightly longer step with the long leg. Infants displayed a variety of adaptation patterns and high variability within each pattern. With increased walking experience, infants showed stronger step length differences between the long and short leg. Adaptive responses are discussed in terms of how change unfolds over time at multiple, nested time scales