Is visual illusion decrement based on selective adaptation?

Illusion decrement is the reduction in the magnitude of visual geometric illusions with continued exposure, and it has been explained in two ways. The first explanation is the selective adaptation, or fatigue, of neural channels carrying orientation and/or spatial frequency information; the second explanation involves perceptual learning, in which the observer changes viewing strategy after continued exposure to a stimulus. Either mechanism could cause changes in the perception of a stimulus over time. One hundred twenty observers were tested in an illusion-decrement paradigm under exposure conditions that altered the amount of selective adaptation of specific neural channels. Observers were also measured on the magnitude of the transfer-of-decrement effect. Both decrement and transfer of decrement occurred, but there was no significant difference across exposure conditions. In addition, the pattern of transfer differed from that observed in selective adaptation paradigms. These results argue against a neural adaptation interpretation of illusion decrement.