‘Where’ depends on ‘what’: A differential functional anatomy for position discrimination in one- versus two-dimensions

• Published in: Neuropsychologia Vol. 38; no. 13; pp. 1741 - 1748
• Main Authors: Fink, Gereon R, Marshall, John C, Weiss, Peter H, Shah, Nadim J, Toni, Ivan, Halligan, Peter W, Zilles, Karl
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 01.01.2000; Elsevier Science
• Subjects: Adult; Anatomical correlates of behavior; Behavioral psychophysiology; Biological and medical sciences; Brain - anatomy & histology; Cognition - physiology; Eye Movements - physiology; Functional Laterality - physiology; Fundamental and applied biological sciences. Psychology; Humans; Judgement; Landmark task; Magnetic Resonance Imaging; Male; Neuroimaging; Psychology. Psychoanalysis. Psychiatry; Psychology. Psychophysiology; Reaction Time; Space Perception - physiology; Visual Fields - physiology; Visuospatial; Visuospatial; Neuroimaging; Landmark task; Judgement; Human; Discrimination; Hemispheric specialization; Position; Vision; Medical imagery; Cognition; Space perception; Laterality; Nuclear magnetic resonance imaging; Judgment; Functional imaging
• ISSN: 0028-3932; 1873-3514
• DOI: 10.1016/S0028-3932(00)00078-6

Line bisection is widely used as a clinical test of spatial cognition in patients with left visuospatial neglect after right hemisphere lesion. Surprisingly, many neglect patients who show severe impairment on marking the center of horizontal lines can accurately mark the center of squares. That these patients with left neglect are also typically poor at judging whether lines are correctly prebisected implies that the deficit can be perceptual rather than motoric. These findings suggest a differential neural basis for one- and two-dimensional visual position discrimination that we investigated with functional neuroimaging (fMRI). Normal subjects judged whether, in premarked lines or squares, the mark was placed centrally. Line center judgements differentially activated right parietal cortex, while square center judgements differentially activated the lingual gyrus bilaterally. These distinct neural bases for one- and two-dimensional visuospatial judgements help explain the observed clinical dissociations by showing that as a stimulus becomes a better, more ‘object-like’ gestalt, the ventral visuoperceptive route assumes more responsibility for assessing position within the object.