No abstract

This paper reports new data on the emergence and development from the 9th to 19th month of age of motor, interactive, and social behaviors of 17 children with peers in a milieu that allows the "conquest" of the third dimension of space without limitation of their motor activity. Their motor skills and social behaviors appear more precocious and complex than previously indicated by scientific publications, clinical observations, and developmental scales. 1. The motor skills that allow the "conquest" of climbing structures (ascents of a spiral staircase and a ramp) are already observed before the age of 12 months in some children (ascents of the ramp) or nearly half of them (ascents of the staircase). Complex social behaviors (multimodal interactions from here and there along a holed partition, imitations, cooperations, anticipation of the behavior of the partner) also emerge before 12 months. 2. The age range from 12 to 14 to 15 months is characterized by consolidation of the motor skills that allow the "conquest" of the third dimension of the space and a rapid increase of the imitations and interactions around the holed partition. 3. The age range from 14 to 18 months is characterized by diversification of the posturomotor patterns during ascents and descents of staircase and ramp and the growing predominance of the standing position. This is also a phase of significant increase in frequency of imitations and cooperations and of emergence of complex forms of cooperation. 4. Aggression is infrequent at all ages.