Faculty Bibliography

Although both infancy and artificial intelligence (AI) researchers are interested in developing systems that produce adaptive, functional behavior, the two disciplines rarely capitalize on their complementary expertise. Here, we used soccer-playing robots to test a central question about the development of infant walking. During natural activity, infants' locomotor paths are immensely varied. They walk along curved, multi-directional paths with frequent starts and stops. Is the variability observed in spontaneous infant walking a "feature" or a "bug?" In other words, is variability beneficial for functional walking performance? To address this question, we trained soccer-playing robots on walking paths generated by infants during free play and tested them in simulated games of "RoboCup." In Tournament 1, we compared the functional performance of a simulated robot soccer team trained on infants' natural paths with teams trained on less varied, geometric paths-straight lines, circles, and squares. Across 1,000 head-to-head simulated soccer matches, the infant-trained team consistently beat all teams trained with less varied walking paths. In Tournament 2, we compared teams trained on different clusters of infant walking paths. The team trained with the most varied combination of path shape, step direction, number of steps, and number of starts and stops outperformed teams trained with less varied paths. This evidence indicates that variety is a crucial feature supporting functional walking performance. More generally, we propose that robotics provides a fruitful avenue for testing hypotheses about infant development; reciprocally, observations of infant behavior may inform research on artificial intelligence.

What do infants learn when they learn to sit upright? We tested behavioral flexibility in learning to sit-the ability to adapt posture to changes in the environment-in 6- to 9-month-old infants sitting on forward and backward slopes. Infants began with slant at 0°; then slant increased in 2° increments until infants lost balance. Infants kept balance on impressively steep slopes, especially in the forward direction, despite the unexpected movements of the apparatus. Between slant adjustments while the slope was stationary, infants adapted posture to the direction and degree of slant by leaning backward on forward slopes and forward on backward slopes. Postural adaptations were nearly optimal for backward slopes. Sitting experience predicted greater postural adaptations and increased ability to keep balance on steeper changes of slant, but only for forward slopes. We suggest that behavioral flexibility is integral to learning to sit and increases with sitting experience.

How do infants plan and guide locomotion under challenging conditions? This experiment investigated the real-time process of visual and haptic exploration in 14-month-old infants as they decided whether and how to walk over challenging terrain - a series of bridges varying in width. Infants' direction of gaze was recorded with a head-mounted eye tracker and their haptic exploration and locomotor actions were captured on video. Infants' exploration was an organized, efficient sequence of visual, haptic, and locomotor behaviors. They used visual exploration from a distance as an initial assessment on nearly every bridge. Visual information subsequently prompted gait modifications while approaching narrow bridges and haptic exploration at the edge of the bridge. Results confirm predictions about the sequential, ramping-up process of exploration and the distinct roles of vision and touch. Exploration, however, was not a guarantee of adaptive decisions. With walking experience, exploratory behaviors became increasingly efficient and infants were better able to interpret the resulting perceptual information in terms of whether it was safe to walk.

We recommend the widespread use of a simple, inexpensive, easy-to-implement, and uniquely powerful tool to improve the transparency and reproducibility of behavioural research - video recordings.

In many situations, multiple actions are possible to achieve a goal. How do people select a particular action among equally possible alternatives? In six experiments, we determined whether action selection is consistent and biased toward one decision by observing participants' decisions to go over or under a horizontal bar set at varying heights. We assessed the height at which participants transitioned from going over to under the bar within a "gray zone"-the range of bar heights at which going over and under were both possible. In Experiment 1, participants' transition points were consistently located near the upper boundary of the gray zone, indicating a bias to go over rather than under the bar. Moreover, transitional behaviors were clustered tightly into a small region, indicating that decisions were highly consistent. Subsequent experiments examined potential influences on action selection. In Experiment 2, participants wore ankle weights to increase the cost of going over the bar. In Experiment 3, they were tested on a padded surface that made crawling under the bar more comfortable. In Experiment 4, we introduced a secondary task that required participants to crawl immediately after navigating the bar. None of these manipulations altered participants' decisions relative to Experiment 1. In Experiment 5, participants started in a crawling position, which led to significantly lower transition points. In Experiment 6, we tested 5- to 6-year-old children as in Experiment 1 to determine the effects of social pressure on action selection. Children displayed lower transition points, larger transition regions, and reduced ability to go over the bar compared to adults. Across experiments, results indicate that adults have a strong and robust bias for upright locomotion.

This article reviews research on the development of motor behavior from a developmental systems perspective. We focus on infancy when basic action systems are acquired. Posture provides a stable base for locomotion, manual actions, and facial actions. Experience facilitates improvements in motor behavior and infants accumulate immense amounts of experience with all of their basic action systems. At every point in development, perception guides motor behavior by providing feedback about the results of just prior movements and information about what to do next. Reciprocally, the development of motor behavior provides fodder for perception. More generally, motor development brings about new opportunities for acquiring knowledge about the world, and burgeoning motor skills can instigate cascades of developmental changes in perceptual, cognitive, and social domains. WIREs Cogn Sci 2017, 8:e1430. doi: 10.1002/wcs.1430 For further resources related to this article, please visit the WIREs website.