Restricted ocular exploration does not seem to explain simultanagnosia.
One major function of parietal cortex is to direct our attention towards salient stimuli. The present data suggest that it also plays an important role in visual gestalt perception. Patients with simultanagnosia following lesions in this area are not able to extract the meaning of a visual scene whereas being perfectly able to recognise individual objects of this scene. We tested two patients with simultanagnosia with hierarchical Navon figures combined with eye movements recordings. The patients' performance allowed us to compare directly the scan paths in trials in which the global letter shape was recognised with trials in which the global letter shape was not recognised. We did not find any obvious differences in the eye movement pattern related to the two perceptual situations. The two patients did not show a significant problem in shifting their eyes (and thus possibly also their attentional focus) to all aspects of the complex visual stimulus when attempting to bind together the different elements of spatially distributed information. The results demonstrate that restricted ocular exploration cannot be the reason for the patients' inability to recognise the global shape of stimuli. Our data rather suggest a role of parietal cortex in visual gestalt perception that is beyond its role of directing attention towards relevant objects.
Clavagnier
Simon
S
Section Neuropsychology, Center of Neurology, Hertie-Institute for Clinical Brain Research, University of Tübingen, Hoppe-Seyler-Str. 3, D-72076 Tübingen, Germany.
Fruhmann Berger
Monika
M
Klockgether
Thomas
T
Moskau
Susanna
S
Karnath
Hans-Otto
HO
D000377:Agnosia / Q000503:physiopathology*; D001288:Attention / Q000502:physiology*; D001931:Brain Mapping; D002540:Cerebral Cortex / Q000473:pathology; D004576:Electromyography / Q000379:methods; D005133:Eye Movements / Q000502:physiology*; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods; D008297:Male; D008875:Middle Aged; D009483:Neuropsychological Tests / Q000706:statistics & numerical data; D010364:Pattern Recognition, Visual / Q000502:physiology*; D010775:Photic Stimulation / Q000379:methods; D049268:Positron-Emission Tomography / Q000379:methods; D013997:Time Factors