An object's axis of elongation serves as an important frame of reference for forming three-dimensional representations of object shape. By several recent accounts, the formation of these representations is also related to experiences of acting on objects. Four experiments examined 18- to 24-month-olds' (N=103) sensitivity to the elongated axis in action tasks that required extracting, comparing, and physically rotating an object so that its major axis was aligned with that of a visual standard. In Experiments 1 and 2, the older toddlers precisely rotated both simple and complexly shaped three-dimensional objects in insertion tasks where the visual standard was the rectangular contour defining the opening in a box. The younger toddlers performed poorly. Experiments 3 and 4 provide evidence on emerging abilities in extracting and using the most extended axis as a frame of reference for shape comparison. Experiment 3 showed that 18-month-olds could rotate an object to align its major axis with the direction of their own hand motion, and Experiment 4 showed that they could align the major axis of one object with that of another object of the exact same three-dimensional shape. The results are discussed in terms of theories of the development of three-dimensional shape representations, visual object recognition, and the role of action in these developments.

Three experiments examine 18- to 24-month-old (N = 78) toddlers ability to spatially orient objects by their major axes for insertion into a slot. This is a simplified version of the posting task that is commonly used to measure dorsal stream functioning. The experiments identify marked developmental changes in childrens ability to preorient objects for insertion, with 18-month-olds failing completely and 24-month-olds succeeding easily. In marked contrast, 18-month-olds preorient their empty hands for insertion into the same slots. This developmental dissociation between aligning hands and aligning objects to slots suggests that the key developmental change is in action with the goal of object-to-object alignment versus action on an object.

Acting on Objects: Integrating Visual and Motor Processes 18-24 months Sandra Street Indiana University Linda Smith Indiana University Abstract: Recent findings indicate substantial changes between the ages of 18- and 24-months in childrens integra- tion of object properties with their actions on objects. Here we report new results from shape sorting and posting tasks in an attempt to understanding how motor and visual developments (or their combination) may contribute to this period of rapid development. Toddlers aged 18-months participated in four experiments involving insert- ing objects into openings. Results suggest that the key developmental achievements reside not in visual or motor developments alone, but in their integration.