The role of left-right symmetry in the encodement of spatial orientations

Three experiments investigated a hypothesis, suggested by studies of the di fficulties of discriminating between shapes forming symmetrical pairs, that spatial orientations of thin flat plates (lamellae) may be encoded in a pl ane, the encodement consisting of two enantiomorphs. The results indicated that participants encoded the spatial orientation of lamellar stimuli in te rms of the difference in cogency between their two enantiomorphic elements (Expt 1). The difference in the cogency of the two enantiomorphs is related to the orientation of the plane containing the lamellar stimulus with resp ect to the participant's fronto-parallel plane (Expt 2). The two possible o rientations of a lamella which yield the same difference of cogency, but wh ich differ in spatial orientation (e.g. lamella 'b' set at 30 degrees or se t at 150 degrees) are distinguished by the manner in which the two enantiom orphic elements are arranged with respect to their axis of symmetry (Expt 3 ). The results suggest that the orientation of a lamella may be encoded as a two-dimensional representation and hence that three dimensions may be enc oded by two by means of enantiomorphs. Implications of this finding for the encodements of three-dimensional solids, wherein pronounced contours may f ulfil the same role as do the edges of lamella, are discussed briefly.