Some observations on the Poggendorff and Müller-Lyer tactual illusions

Abstract

Two experiments were conducted in which illusory and nonillusory figures were presented in the right and left tactual fields. Experiment 1 used 24 men (aged 18-24 years) and the Poggendorff (P) illusion and an alignment (Al) task; Experiment 2 used another 24 men and the Müller-Lyer (ML) illusion and a line-match (Lm) task. Standard and mirror-image presentations of the figure were used in each case. Nested designs of analysis of variance and analysis of covariance were adopted for comparing left- and right-hand performance under each experimental condition. Covariance analysis on distortion scores of P and ML was performed separately with discrepancy measures on Al and Lm tasks as covariates. An investigation was also made into whether the direction of tactually perceived distortions was the same as or opposite to that reported for the visual illusions. The results show large P and ML tactual distortions. For ML, the tactual effects found were similar to those predictable from visual illusions, whereas for P, a high value of inversion emerged. Differences between hands were significant for P under the standard presentation, exploration with the right hand inducing a higher value of inversion. The latter results are discussed with reference to differences between the functions of human hemispheres which some authors have suggested for perceptual distortions. © 1986 Psychonomic Society, Inc.