Fatigue versus disengagement in unilateral neglect.

A letter cancellation task revealed neglect of the lower left quadrant when cancellation began at the top, but of the upper left quadrant when it began in the bottom. When the cancellation was done line by line through a "window" which covered all but the line currently worked on, the quadrant effects disappeared, so that fatigue could not explain these effects. An alternative hypothesis is that as the cancellation progressed, the subject's attention was attracted by progressively more stimuli on the right, and that disengagement difficulty and hence neglect increased proportionately to the number of stimuli.