This longitudinal study investigates infants' touching behaviors with others during naturalistic observations in a daycare center in Japan. Interactions between eight infants and their caretakers during free play time were videotaped. The obtained data were examined based on infants' postures and the body parts used to engage in interpersonal touch during locomotor development. As the locomotor period progressed from crawling to walking, the infants made bodily contact more frequently. When they were crawlers, incidental touch occurred often, but with progress in locomotion, purposeful (instrumental and social) touch became more common. Infants' purposeful touch occurred more frequently when they used their hands than when they used other body parts to touch. Touching with hands was more frequent when (a) infants who were able to walk were in walking postures than when they were unable to walk and in crawling postures; (b) infants who could walk were in sitting postures than when they could not walk and were in sitting postures, and (c) infants who could walk were in standing postures than when they were in sitting postures. Infants' locomotor development freed infants' hands from locomotion, and overall progress in physical coordination helped infants maintain balance. These advances in motor development made infants' touch behaviors social.
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