Mechanisms of unilateral spatial neglect in copying a single object.

The present study examined 13 patients with typical left unilateral spatial neglect to explore the mechanisms of neglect in copying a single object. All patients identified the figure of a sunflower as a flower that had petals all around the central circle. Besides, in the free viewing of the flowers prepared by the examiner, 10 of the 13 patients could discriminate between the presence and absence of the left-sided petals. When copying the flower, however, they always left the left side unfinished without noticing the incompleteness. Whether perception in the left visual field was impaired or not was irrelevant to the performances in the copying and the free viewing of the flowers. We consider the mechanism of left unilateral spatial neglect in copying a flower as follows. Small leftward shift of attention may take place during the free observation of the stimulus flower. While copying, however, neglect patients pay attention exclusively to the right-sided petals they are drawing. The strong engagement of attention to the right side results in the lack of discovery of the left-sided omission. The close integration of attentional and premotor mechanisms seems to be crucial for the appearance of unilateral spatial neglect in copying a single object.