Dissociation between temporal and spatial variability in locomotor development

Infant motor development is characterized by high variability; during locomotion, spatial and temporal aspects of locomotor coordination seem to change on every step. Such continuous variability could serve an exploratory function analogous to exploration-driven reinforcement learning. However, we need further insight into the structure of this variability to enable careful comparison with computational models of learning and their underlying assumptions. In this study, we identify structured signatures of spatial and temporal variability in infant locomotor patterns. Natural walking data were collected from 16 children ($9-45$ months) and compared to 9 adults. Analyses revealed a surprising dissociation between spatial and temporal variability; while children, like adults, exhibit a strong speed-dependent stride length relationship, they exhibit a much weaker speed-dependent stride frequency relationship. This observed dissociation between spatial and temporal variability poses a question for models of locomotor learning: under what assumptions might models exhibit a similar dissociation? Future modeling studies could test multiple hypotheses to explain this observation such as distinct underlying mechanisms for spatial and temporal exploration or faster learning enabled by sequencing spatial and temporal exploration inspired by infants.