Learning to walk is still an "old" problem: a reply to Zelazo (1983).
Zelazo (1983) proposes that two cognitive prerequisites are necessary for the development of locomotion: The conversion of neo-natal reflexive stepping into instrumental behavior and a shift from stereotypical to relational play. I argue that these cognitive assumptions are unnecessary. The disappearance of neo-natal stepping can be explained as a result of increasing leg mass, and the retention of this reflex with practice may be simply an exercise effect. Comparative and evolutionary evidence suggests that locomotion is not associated with abstract reasoning ability. Learning to walk is a complex, gradual process of maturation of motivation, the integration of subcortical pattern-generating centers with the neural substrate for control of posture and balance, and important changes in body proportions and bone and muscle strength. The control of walking is likely the province of mechanism phylogenetically more primitive than the human cerebral cortex. There is no need to invoke cortical explanations when more simple ones are sufficient.
Thelen
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Department of Psychology, University of Missouri, Columbia 65211, USA.