The vertical-horizontal illusion: assessing the contributions of anisotropy, abutting, and crossing to the misperception of simple line stimuli.

Mamassian and de Montalembert (2010) have proposed a simple model of the vertical-horizontal illusion. This model identified two components, an anisotropy which results in horizontal lines being perceived approximately 6% shorter than verticals and a bisection component which results in a bisected line being perceived approximately 16% shorter. We have shown that this bisection component confounds two effects: One when lines cross one another and a second effect when one line abuts another. We propose an extension to the Mamassian-de Montalembert model in which their bisection component is replaced by separate crossing and abutting components.