Effects of illusory spatial anisometry in unilateral neglect

• Published in: Experimental brain research Vol. 154; no. 2; pp. 226 - 237
• Main Authors: Ricci, Raffaella, Pia, Lorenzo, Gindri, Patrizia
• Format: Journal Article
• Language: English
• Published: Berlin Springer 01.01.2004; Springer Nature B.V
• Subjects: Aged; Aged, 80 and over; Biological and medical sciences; Female; Functional Laterality - physiology; Humans; Illusions - physiology; Male; Medical sciences; Middle Aged; Nervous system (semeiology, syndromes); Nervous system as a whole; Neurology; Neuropsychological Tests; Parietal Lobe - physiopathology; Perceptual Disorders - physiopathology; Perceptual Disorders - psychology; Photic Stimulation; Psychomotor Performance - physiology; Space Perception - physiology; Visual Cortex - physiopathology; Visual Fields - physiology; Visual Pathways - physiopathology; Human; Nervous system diseases; Spatial neglect; Anisometry; Perceptual illusion; Visual illusions; Space perception; Milner Landmark task; Eye disease; Stimulus distance; Modulation; Visuospatial neglect; Optical illusion; Neurological disorder
• ISSN: 0014-4819; 1432-1106
• DOI: 10.1007/s00221-003-1650-y

Patients with visuospatial neglect tend to underestimate horizontal magnitudes in contralesional space. It has been recently hypothesised that this behaviour might be due to anisometry of space perception, by which horizontal stimuli would be progressively underestimated proceeding from the ipsi towards the contralesional side of space. We investigated the effects of modulating space perception through the Oppel-Kundt illusion (i.e. a filled space is perceived as more expanded than an empty space) on the behaviour of 28 neglect patients and 28 normal subjects. The two groups bisected lines on backgrounds of vertical lines evenly spaced or unevenly spaced, with distances which decreased progressively from one side of the page to the other. On the same backgrounds, they extended segments to the left or to the right so as to double them. Patients also had to cancel targets, the density of which was evenly distributed or horizontally increased from one side of the page to the other. Both groups were prone to the illusion. Neglect bias was modulated by the illusion in the expected direction. It was reduced when the illusion induced a perceptual distortion opposite to that thought to underlie neglect. On bisection and cancellation tasks, illusory effects were greater in patients with higher values of response bias on the Milner Landmark task. These findings, taken together with patients' anatomical data, suggest that a modulation of neglect through a visual illusion can normally be induced in patients with relatively intact visual input processes.