Robert A. M. Gregson, Australian National University

Abstract: Two experiments exploring similarity judgments on pairs and triplets of stimuli drawn from pictorial series are described. The stimuli are the Man-Woman and Gypsy-Girl pictures that slowly change from one prototype to the other as one progresses along the series. These have been used previously to demonstrate hysteresis of category judgments on ambiguous figures; the Man Woman series has been both modelled as a problem in neural network theory and mapped onto part of a cusp catastrophe surface. It. is shown that the transition process is complica-ted with a zone of uncertainty and prevalence of bimodality in many of the pairwise similarity judgments. The dynamics are interpreted in terms of transitions between two saddle-node attractors that are themselves not a discrete pair but have some overlap in their composition.

Keywords: similarity, boundaries, intransitivities, attractors