Is one hand always better than two? A replication study

Recently, it has been shown that the active movement of the left hand in the left hemispace reduces left neglect in visual exploratory tasks. Despite the important theoretical and practical implications, there exists no direct confirmation of these findings in the literature. To verify the presence of the beneficial effect of left hand movement in left space, we replicated three of the nine experiments devised by Robertson and North (Neuropsychologia 1992; 30: 553-63, Neuropsychologia 1994; 32: 1-11). To this end, we tested 10 consecutive patients with right brain damage and left neglect. We found the expected pattern of performance in only one patient: on reading and cancellation the total number of omissions significantly decreased when irrelevant movements were performed with the left hand in the left space. This finding underlines the importance of replication studies in cognitive neuropsychology.