A quantitative analysis of illusion magnitude changes induced by rotation of contextual distractor

In the present study, the predictions of the computational model of centroid extraction were verified in psychophysical examination of the length illusion induced by stimuli comprising the conventional or asymmetric Müller-Lyer wings as the contextual distractors. In experiments, the illusion magnitude changes evoked by rotation of distractors with different spatial parameters were quantitatively determined. It was demonstrated that the model calculations adequately account for the illusion magnitude variations shown by all the subjects for all modifications of stimuli. A good correspondence between the experimental and theoretical data supports the suggestion that local positional biases caused by the neural processes of automatic centroid extraction can be one of the main reasons of emergence of illusions of the Müller-Lyer type.