Apparent reversals in trapezia: confirmation of the 'tan apex ratio' heuristic.

A new model for predicting the frequencies of apparent reversals in rotating trapezia, proposed by the authors in 1983, is validated and extended in two studies. Experiment 1 showed that the model retained its predictive efficiency over an increased range of shapes and viewing distances, and with trapezia made of sheet metal and not, as previously, of wire. Experiment 2 was designed to investigate an unexpected effect, in which the specificity of prediction was found to decrease as the corners of the stimulus objects were slightly rounded.