Differences between reflexive and voluntary eye movements in patients with neglect

M. Niemeier, H.O. Karnath

Department of Neurology, University of Tübingen, Hoppe-Seyler-Strasse 3, D-72076 Tübingen, Germany (e-mail:niemeier@uni-tuebingen.de)

Oculographic analyses in patients with neglect have provided evidence for a direction-specific deficit of saccadic orienting. When required to perform reflexive eye movements towards targets in the left and right periphery saccades in contralesional direction showed (a) increased reaction times, (b) were hypometric, and (c) were increased in number creating a 'staircase pattern' of saccadic eye movements. One might assume that these deficits are associated with a general impairment in disengaging attention before shifts in the contralesional direction which has been discussed as the mechanism underlying neglect. If so, affected contralesional saccades should be observed not only with sudden appearance of peripheral targets but also in spontaneous visual search. In the present study we analysed (i) reflexive saccades towards targets suddenly appearing in the periphery and (ii) voluntary saccades during free exploration of space. As in previous studies, neglect patients showed a direction-specific 'staircase pattern', i.e. contralesional saccades were hypometric and increased in number. However, during free exploration of space we found no evidence for a direction-specific deficit, neither for the number of saccades nor for the average duration of fixation. Saccade amplitude was reduced regardless of direction. In conclusion, we found no indication for a general direction-specific deficit of saccadic eye movements in neglect. The results argue against an interpretation of neglect as a basic deficit to disengage from an attentional focus to a target located in the contralesional direction.