Illusions and aftereffects of length in the minimal form of the parallel-lines configuration: a reexamination.

A number of recent studies have used the graded-series method to measure the illusion and aftereffect distortions of perceived length in the minimal form of the parallel-lines configuration. However, because of some peculiar characteristics of the graded-series method, the aftereffect distortions measured with this method cannot be interpreted unequivocally as reflecting distortions of the perceived length of the test line. On the basis of the results of an experiment that examined the contribution of a possible confound present in the method, it is argued that the method should not be used to measure length aftereffects, and, furthermore, that the results of studies using this method need to be reconsidered.