Influence of instructions and cognitive articulation on reducing the Müller-Lyer illusion with a repeated trial.

The role of specific, suggestive instructions and of the subject's cognitive articulation in fostering modifications of Müller-Lyer illusory effect was studied. 60 female students were divided into four subgroups on the basis of (a) Witkin's GEFT scores and (b) instructions given to the subjects for the repeated trial. Analysis shows no statistically significant difference between the more and less articulated subjects on the first trial, for influence of both cognitive articulation and instructions or their interaction on the reduction of the illusion. Data are interpreted in terms of some theoretical explanations of geometrical illusions, such as 'centration theory' and 'assimilation theory'.