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Non-spatial extinction following lesions of the parietal lobe in humans
Humphreys, G., Romani, C., Olson, A., Riddoch, M.J. & Duncan, J.
Nature, 372, 357-359
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Efficient behaviour in the visual environment requires selection between stimuli competing for control of action. Many current models of selection are spatial: relevant objects are chosen through attention to their locations. Strong evidence for spatial selection is unilateral extinction following lesions of the parietal lobe. Though patients may identify a single stimulus presented in their contralesional field, they can fail to detect the same stimulus when a competing stimulus occurs simultaneously on the ipsilesional side. Here we demonstrate that extinction need not be spatial in nature, but may be determined by characteristics of the objects to be selected. In two patients with parietal lobe lesions and poor spatial localisation, pictures extinguished words and closed shapes extinguished open shapes. This object-based extinction indicates the existence of biases within non-spatial selection mechanisms which are independent of biases produced by spatial selection mechanisms. We suggest that selection of objects for action requires binding together the winners produced by the independent competitive biases for selection within distinct neural areas concerned with object properties and space.