Neglect of chimeric figures: two halves are better than a whole.

From a group of 22 patients with neglect, we identified five patients who neglected the left sides of "chimeric" figures composed of the conjoined right and left halves of drawings of two different objects; these subjects reported the left half-drawing significantly more accurately when a gap was introduced between the chimeric halves. The improvement in the "gap" condition cannot be attributed to the subjects' recognition that the right-sided stimuli were incomplete, as when whole figures were presented on the right along with left-sided half figures, the enhancement in reporting accuracy was maintained. For at least one patient, sufficient information was available about the neglected stimuli to support accurate recognition in a forced-choice task with foils visually similar to the targets. On the basis of these and other data, we propose that for these patients with neglect, visual processing systems subserving the registration of discrete object markers in a spatial map are at least relatively intact, but that there is an impairment in the allocation of attention to the left sides of these markers.