Local luminance factors that determine the maximum disparity for seeing cyclopean surface shape

We measured the maximum disparity grating amplitude (d(max)) for seeing cyc lopean surface shape, using stereograms made from dense arrays of micropatt erns, whose luminance characteristics were manipulated. In Experiment 1, we used disparity gratings made from Gabor micropatterns. D-max was found to vary inversely both with luminance spatial frequency and with Gabor size, b ut was constant for a constant bandwidth (frequency times size). To test wh ether this was due to changes in bandwidth per se or to changes in the numb er of local features, in Experiment 2 we manipulated the local feature cont ent with a range of micropatterns that we termed 'edgels'. The results supp orted neither hypothesis. In Experiment 3 we varied the phases of the Fouri er components of square wave edgels, thereby introducing more features, and we found that this did not change d(max). Taken together, our results show that d(max) decreases with an increase in the number of local luminance cy cles at each luminance scale. D-max is mainly limited by false target match ing between similar components of the micropatterns. Stereopis, in terms of surface shape perception, is served only by first order mechanisms, and on ly by luminance filters that are broadband. (C) 2000 Elsevier Science Ltd. All rights reserved.