Fernando Castillo Rodriguez¹, Joseph DeNavas², Arthur G Shapiro², Cathleen M Moore¹; ¹University of Iowa, ²American University

In the Müller-Lyer (ML) illusion, the separation between two wings-out arrow heads is perceived as greater than the identical separation between two wings-in arrow heads. We asked whether this difference in perceived separation was functional in that it would transfer to differences in perceived speed. Specifically, we asked whether the speed of an object moving between two wings-out arrow heads would be perceived as greater than the speed of an identically moving object between two wings-in arrow heads. Using both linear (Brentano) and circular (Todorović) ML displays, large differences in perceived separation were found between wings-out and wings-in arrowheads. The perceived speed of moving discs within the same displays, however, was unaffected by the direction of the arrow heads, and was generally accurate. Thus, the motion system was blind to perceived differences in separation due to the ML illusion. This indicates that the ML illusion does not give rise to functional representations of different separations, as mechanisms of size constancy do. These results, therefore, challenge explanations of the ML illusion that appeal to size constancy.