Unilateral neglect can be affected by stimuli in the neglected field

Neglect patients' attention is usually pathologically captured by stimuli present on the side ipsilateral to the brain damage. In previous research it was shown that not only the mere presence but also the number of "relevant" stimuli on the right side influenced patient's performance. However, the influence of stimuli whose presence was completely irrelevant for the execution of the task was not previously studied. We asked neglect patients to bisect lines of 28 cm of length, which could be presented alone or with line-drawings of objects placed either only on the left, only on the right or bilaterally on the display. We found that the presence of irrelevant left-side stimuli improved the bisection performance in 3 out of 5 patients with respect to the baseline condition, in which, no stimuli were present on either side of the display. Right-side stimuli did not affect the performance, whereas bilateral stimuli tended to worsen the performance for those patients who presented the beneficial effect of left-side stimuli. These findings were discussed with reference to the hypotheses advanced to explain neglect.