RÉSUMÉ
<p><b>OBJECTIVE</b>The Muller-Lyer illusion is a visual illusion in which a horizontal shaft with an inward-pointing chevron (fins-out) affixed to each end is perceived longer than a shaft with outward-pointing chevrons (fins-in). The goal of this study was to compare the effects of experience and knowledge about the Muller-Lyer illusion on participants' perceptual precision.</p><p><b>METHODS</b>Participants were undergraduate students (n = 108) who were not familiar with the Muller-Lyer illusion prior to the experiment. The task of participants was to adjust one movable line to make it equal to the other in Muller-Lyer figure. They received ascending and descending Muller-Lyer trials in three blocks with 20 trials each. The Experimental Group received information about the Muller-Lyer illusion prior to the third block.</p><p><b>RESULTS</b>For the Experimental Group, the amount of departure in Block 3 was reduced significantly compared with previous blocks.</p><p><b>CONCLUSION</b>Knowledge about the mechanisms underlying visual illusions may play an important role in helping individuals overcome them.</p>