Induction-, test-, and comparison-figure interactions under illusion and figural aftereffect conditions

Ganz (1966a, b) has argued that an induction figure will displace a test figure placed near it under both illusion and figural aftereffect conditions. The data from Experiments I and II show that most of the illusion produced by the figures studied by Ganz results from an interaction between the comparison and induction figures. The data from Experiment III suggest that both the test and comparison figures interact with the induction figure under figural aftereffect conditions. Although the induction-test figure interactions do not contradict Ganz’s model, the induction-comparison figure interactions cannot be explained by it. The data also suggest that researchers should be extremely cautious in drawing conclusions about the processes underlying illusions and figural aftereffects unless they are confident that there is no interaction between the induction and comparison figures.