Perception-action and the Müller-Lyer illusion: amplitude or endpoint bias?

Over the past decade there has been a great deal of controversy regarding the relative impact of visual illusions on cognitive judgments and the control of goal-directed action. We report the results of two experiments indicating that perceptual biases associated with the Müller-Lyer illusion involve a misjudgment of amplitude/extent while aiming biases involve error in the specification of a movement endpoint. This dissociation of perception and action is consistent with some aspects of Milner and Goodale's two visual system model, but not others.

The Müller-Lyer illusion affects the planning and control of manual aiming movements.

Participants made perceptual judgments about the length of, and manual aiming movements to the opposite end of, formerly visible Müller-Lyer stimuli. The Müller-Lyer illusion affected both perceptual judgments and aiming amplitude. Manipulations of stimulus duration (10 ms or 3000 ms) and memory delay length (10 ms or 3000 ms) had no impact on the illusory effect.