Mental rotation and mirror-image discrimination.

Two experiments involving judgments of same-different were conducted to assess conditions in which mental rotation is used. These two experiments were similar except in the way "different" pairs were constructed. In the first experiment, a "different" pair involved two different polygons; in the second one, a "different" pair involved one polygon and its mirror-image. The strategy used by the 8 subjects was investigated through patterns of reaction times. The first experiment exhibited a flat function of reaction times with orientation, whereas the second one exhibited a linear increase in reaction times with angular departure from upright. These results lead to the conclusion that mental rotation is used when a figure has to be distinguished from its mirror-image.