Assimilation theory, attentive fields, and the Müller-Lyer illusion

The assimilation theory of geometric illusions was employed to predict changes in the outgoing and ingoing forms of the Mûller-Lyer illusions as a function of attentive field size. It was found that the theory predicted correctly the form of the function relating amount of illusion and size of attentive field only for the outgoing Müller-Lyer. For the ingoing illusion the prediction was opposite to the empirically obtained results. The findings are seen as additional evidence for the untenability of a unitary theory, such as assimilation theory, for both versions of the Müller-Lyer illusion as they fail to account for substantial difference between them.