Effects of unilateral hemispheric lesions on two types of optico-geometric illusions

Two optico-geometrical illusions--the Müller-Lyer (ML) and the Ponzo (P) illusion--have been studied in normal subjects and in patients with unilateral cortical lesions. Patients with left-sided lesions have stronger illusions than normal subjects, the increase being significant only for the ML illusion. In the case of right-sided lesions, the P illusion is weakened while the ML illusion is equivalent to that of control subjects. The findings are discussed in relation to the mode of apprehension of information.