Mechanisms of spatial attention revealed by hemispatial neglect

We report performance by a patient, NG, with hemispatial neglect after nond ominant stroke, in detecting briefly (200 msec) presented visual targets. N G's detection of targets (gaps in circles) was determined by the location o f the target in the space in which stimuli appeared. Gaps on the neglected side of a circle at fixation were rarely detected when circles of uniform s ize were always presented at fixation. The same targets in the same locatio n were detected far more often in blocks that also included targets present ed on each side of the central circle, or in blocks that included larger ta rget stimuli. In these blocks, the window of space in which stimuli appeare d was larger, such that the target fell closer to the center of this "windo w". These results indicate that the spatial extent of attention, and of hem ispatial neglect, can be modified on the the basis of expectations and task requirements.