Decrement of the Müller-Lyer and Poggendorff illusions: the effects of inspection and practice.
Five experiments assessed the decline or decrement in illusion magnitude for the wings-out form and the combined or Brentano form of the Müller-Lyer illusion, and for the Poggendorff illusion. Judgments were obtained under conditions of either continuous or intermittent inspection of the illusion figure. In the continuous-inspection conditions observers scanned the illusion figure during the inter-trial intervals whereas in the intermittent-inspection conditions they did not. Substantial illusion decrement was found in all continuous-inspection conditions and in intermittent conditions with short inter-trial intervals (upto 20 s) but not with longer inter-trial intervals. However, intermittent-inspection with a long inter-trial interval (40 s) produced illusion decrement but only when observers were instructed during the decrement session to ignore the wings, and pay attention to the shaft, of the Müller-Lyer figure. Taken together, the pattern of results does not support the claim that illusion decrement is primarily a product of practice or repeated trials.
Predebon
John
J
Department of Psychology, University of Sydney, NSW, 2006, Australia. johnp@psych.usyd.edu.au
D006801:Humans; D009903:Optical Illusions; D010507:Periodicity; D011214:Practice, Psychological; D013997:Time Factors; D014796:Visual Perception