A masking analysis of glass pattern perception.

A Glass pattern consists of randomly distributed dot pairs (dipoles) whose orientations are determined by a geometric transform. To understand how an observer perceives the global structure, we investigated how the threshold for detecting a concentric or a radial Glass pattern (target) can be affected by the presence of another Glass pattern (masker). The Glass patterns had either concentric, radial, vertical, plaid, or spiral global forms. We used a 2AFC paradigm in which a mask was presented in both intervals while a target was randomly presented in one interval and a random dot pattern in the other. The target dot density thresholds were measured at 75% accuracy. For all masker types, the target threshold was constant at low masker densities and then increased with masker density. For concentric targets, concentric and spiral maskers had the best masking effect. For radial targets, a low-curvature spiral mask produced the best masking. The target threshold versus masker density functions were fit with a divisive inhibition model, in which the response of a global mechanism is the excitation of a linear template to the input image raised by a power and divided by the sum of an inhibition input and a constant.