Infants' developing motor skills promote perceptual exploration and learning as part of a nested developmental cascade. A set of three papers shows that postural development facilitates multimodal object exploration, which, in turn, induces infants' learning about objects' three-dimensional (3D) forms. Concurrently, upright posture and coordinated visual-manual exploration support the regulation of infants' motor commands.;Paper 1 shows that 3D object completion emerges at around 6 months of age. Infants at 4 and 6 months of age were habituated to a computer-generated 3D object shown from a single viewpoint. Only the 6-month-olds showed a post-habituation novelty preference for an incomplete object missing a back side, implying that they perceived the limited-view object as a complete volume. Infants in a control task showed no spontaneous visual preferences for either test display.;Paper 2 indicates that exploration of objects from multiple viewpoints supports development of 3D object completion. Infants between 4.5 and 7.5 months of age completed a replication of the habituation task from Paper 1 and a motor skill assessment. Infants with more days of independent sitting experience and who displayed more coordinated visual-manual exploration showed stronger novelty preferences for the incomplete object display. Moreover, self-sitting infants manipulated objects more often while looking at them than not looking, but non-sitters explored objects equally often with looking and without.;In Paper 3, infants spontaneously mirrored movements of the manipulating hand with their free hand and legs during one-handed object exploration. The presence of these extraneous overflow movements suggests that the immature motor system is ineffective in relegating motor commands to the appropriate side of the body. Young infants exhibit motor deficits similar to persons with neurological damage. However, overflow movements were reduced in a sitting posture compared to lying supine on the back and when infants looked at objects while manipulating them. Over time, sitting upright and coordinating visual and manual exploration may reduce extraneous movements, guiding neural maturation and promoting skilled manual actions.
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