Hemispheric differences in spatial relation processing in a scene perception task: a neuropsychological study.

Understanding a complex visual scene depends strongly on our ability to process the spatial relations between objects in that scene. Two classes of spatial relations can be distinguished. Categorical information concerns more abstract relations, like "left of", while coordinate information is metric and more precise, such as "2cm apart". For categorical processing a left hemisphere advantage is typically found, and coordinate processing is linked to a right hemisphere advantage. However, this has scarcely been investigated in more naturalistic settings. The aim of the present study was to explore spatial relation coding in natural scenes as well as to gain more insight in hemispheric differences in processing categorical and coordinate position changes, by testing patients with unilateral stroke. By means of a comparative visual search task using images of rooms, a healthy control group (N=28), patients with left hemisphere stroke (LH) (N=16), and patients with right hemisphere stroke (RH) (N=17) were tested on their ability to detect position changes that were either only coordinately different (coo), or both coordinately and categorically different (coo+cat). The response pattern of the control subjects confirmed previous findings that both coordinate and categorical information contributed to position change detection. Compared to the control group, the RH patient group showed an impairment on both coo and coo+cat position changes. In contrast, the LH patient group was not impaired on the coo condition and showed only a trend of impairment on the coo+cat condition. These response patterns suggest that lateralisation patterns found in previous, more simple and controlled experiments are also present to some degree in a more complex and lifelike setting.