Illusion decrement and transfer of illusion decrement in Müller-Lyer figures

In the work reported in the literature the reduction or decrement in the magnitude of the Müller-Lyer illusion with continued inspection has been typically investigated with the use of the composite illusion form. Three experiments are reported in which the illusion decrement was separately examined in the underestimated (wings-in) and the overestimated (wings-out) forms of the Müller-Lyer illusion, with particular attention paid to the transfer of illusion decrement between the two forms. Decrement occurred in both forms of the Müller-Lyer illusion, although there was considerable intersubject variability in decrement effects, and nonuniform rates of decrement across the inspection period. In none of the experiments did transfer of illusion decrement between the two forms occur. It is argued that the attentional/differentiation hypothesis of illusion decrement provides a plausible account of the present findings as well as of those found with the composite Müller-Lyer figure.