Global shape recognition is modulated by the spatial distance of local elements--evidence from simultanagnosia.
Simultanagnosia is a rare deficit that impairs individuals in perceiving several objects at the same time. It is usually observed following bilateral parieto-occipital brain damage. Despite the restrictions in perceiving the global aspect of a scene, processing of individual objects remains unaffected. The mechanisms underlying simultanagnosia are not well understood. Previous findings indicated that the integration of multiple objects into a holistic representation of the environment is not impossible per se, but might depend on the spatial relationship between individual objects. The present study examined the influence of inter-element distances between individual objects on the recognition of global shapes in two patients with simultanagnosia. We presented Navon hierarchical letter stimuli with different inter-element distances between letters at the Local Scale. Improved recognition at the Global Scale was observed in both patients by reducing the inter-element distance. Global shape recognition in simultanagnosia thus seems to be modulated by the spatial distance of local elements and does not appear to be an all-or-nothing phenomenon depending on spatial continuity. The findings seem to argue against a deficit in visual working memory capacity as the primary deficit in simultanagnosia. However, further research is necessary to investigate alternative interpretations.
Huberle
Elisabeth
E
Section Neuropsychology, Department of Cognitive Neurology, Hertie-Institute for Clinical Brain Research, University of Tübingen, Hoppe-Seyler-Strasse 3, D-72076 Tübingen, Germany.
Karnath
Hans-Otto
HO
D000377:Agnosia / Q000503:physiopathology*; D001288:Attention / Q000502:physiology; D001931:Brain Mapping; D016022:Case-Control Studies; D005260:Female; D006801:Humans; D008875:Middle Aged; D010364:Pattern Recognition, Visual / Q000502:physiology*; D010775:Photic Stimulation / Q000379:methods; D049268:Positron-Emission Tomography; D011601:Psychophysics; D021641:Recognition, Psychology / Q000502:physiology*; D013028:Space Perception / Q000502:physiology*