Changing attentional demands in left hemispatial neglect
R. F. Kaplan, M. Verfaellie, M. E. Meadows, L. R. Caplan, M. S. Pessin and L. D. DeWitt
Department of Neurology, Tufts University School of Medicine, Boston, Mass.
Seven variations of a letter cancellation test were used to examine how
varying attentional demands affect hemispatial neglect in patients with
right hemisphere lesions. While the 14 targets always remained in the same
location, the number of distractors (zero, nine, 28, or 82) as well as
their complexity (one letter or nine different letters) were varied. The
percentage of targets canceled in the left hemispace was linearly related
to the number of distractors. There were no differences between the
complexity conditions. In a second study, the same 14 targets were
presented but the distractors (zero, 14, or 41) were all placed on the
right. Increasing the number of distractors on the right increased neglect
on both sides of the space. Taken together, these results suggest that,
while the limited attentional resources of the left hemisphere are biased
toward the right hemispace, the absence of contralateral attentional
demands allows these resources to be directed ipsilaterally.
