An Analysis of Illusion Components with ⌞ and ⊥ - Figures in Active Touch

Abstract

The influence of radial movement in haptically explored ⌞ and ⊥-figures is investigated by tilting them from the frontoparallel to the horizontal plane. Inclining an upright ⌞-figure towards the horizontal plane leads to an illusion that increases with the degree of inclination (Experiment I). The same curve, only shifted upwards, is found with a ⊥-figure (Experiment II), indicating an additive bisection effect. A theoretical function relating illusion magnitude and angle of inclination is presented. The results confirm an interpretation of the illusion in terms of radial and tangential components of arm movements. The implications of these results are discussed in relation to theoretical explanations of the haptic and visual form of the horizontal-vertical illusion.