Abstract :
We will demonstrate possible and impossible response alternatives in the Piaget three-mountains task. The response alternative in the foreground in the demo photograph is impossible. The response alternative in the background is possible. In the Piaget three-mountains task, a cube, a sphere, and a cone are placed on a table. Response shapes, in relief, are a square, circle and triangle. Observers are given front, side and back views and decide which is which. The task is commonly used to assess spatial skills in the blind and blindfolded, children and adults. We point out that if there are three objects, there are six orders. Two of the orders are impossible, in any given arrangement of the three objects. We find that blindfolded observers are faster and more accurate in judging the front view than the impossibles, but the impossibles are on a par with other views.
