Affiliations: Department of Psychology, Carnegie Mellon University,
PA, USA | Department of Neuroscience, University of Pittsburgh,
PA, USA | Department of Information Science, University of
Pittsburgh, PA, USA | Department of Statistics, Carnegie Mellon University,
PA, USA
Note: [] Corresponding author: Marlene Behrmann, Department of
Psychology, Carnegie Mellon University, Pittsburgh, PA 15213-3890, USA. E-mail:
behrmann+@cmu.edu
Abstract: Patients with unilateral neglect are impaired at making saccades to
contralesional targets. Whether this problem arises from a deficit in
perception, in planning the saccade or in executing the eye movement or some
combination thereof remains unclear. We measured several variables related to
the initiation and execution of saccades in an experiment which crossed two
factors: target side (left, right) and direction of saccade (leftwards,
rightwards). Relative to control subjects, patients with left-sided neglect
were impaired in planning but not executing the contralesional saccade; while
the latency to move their eyes following the onset of the target was increased,
the duration and velocity to reach the target were normal. In addition, there
were also no directional differences for saccades that were hypometric or
inaccurate in the patients, further ruling out an execution impairment.
Interestingly, this directional initiation deficit was exaggerated for leftward
saccades to left targets, compared with all other conditions. We suggest that
the disadvantage for contralesional saccades in neglect patients is
attributable to a deficit not only in perceiving contralateral targets but also
in planning leftward saccades. Once the saccade is initiated, however,
execution apparently proceeds unimpaired.
