Evidence for the use of scene-based frames of reference in two-dimensional shape recognition.

A series of reaction time (RT) experiments are reported in which subjects had to match pairs of two-dimensional shapes. The shapes were either symmetrical or asymmetrical and were arranged into either symmetrical or asymmetrical displays. In the initial experiments the shapes straddled the vertical midline of the display. It was found that Same RTs to symmetrical displays were shorter than Same RTs to asymmetrical displays, and that Same RTs to symmetrical shapes were shorter than Same RTs to asymmetrical shapes. Moreover, display symmetry and shape symmetry produced an additive effect on responses. This pattern of results obtained when both shapes were presented simultaneously and when a delay was introduced between the presentation of one shape and the presentation of the other. However, display and shape symmetry interacted when the displays were rotated 90 deg within the plane so that the shapes straddled the horizontal meridian. The implications of these results are discussed in terms of both a transformational account of shape recognition and an account concerning the imposition and use of scene-based frames of reference.