Abstract
A segmented container called the V-box was designed to train adult subjects who fail a Piagetian type measure of the horizontality concept. The first segment appears round when viewed from straight on and virtually all adults were able to predict correctly how the water line would appear when this segment was half filled with water. Partitions can be removed and the water allowed to fill up the entire container which has straight-line boundaries. On a pretest, 28 of 43 subjects failed to indicate the water line correctly on the container, when its straight-line characteristics were apparent. Of these 28, 18 were able to do so after being exposed gradually to the container's rounded segment and, step by step, to its elongated segments with straight-line boundaries. The difference in pre- to posttest change in performance between these 18 subjects and the 10 control subjects was significant.