The tilt illusion as a function of the relative and absolute lengths of test and inducing lines

The explanation of the tilt illusion that attributes the effect to lateral inhibitory interactions between cortical orientation-selective neurons suggests that illusion magnitude is dependent in part upon the lengths of the inducing (I) and test (T) arms of an angle. The model predicts (1) larger illusions for I length > T than for T > I; (2) that when I=T, peak illusion magnitude will occur for smaller angles between I and T when these lines are long than when they are short; and (3) that when I=T, smaller peak illusions for long lines than for short lines. Two experiments were conducted to test these predictions, and the results were consistent with all but the last of them. It is suggested that the aspect of the model that attributes perceived line orientation to the most active neurons stimulated by a line (the mode of the response function) requires reexamination.