Brain Advance Access published online on September 28, 2007
Brain, doi:10.1093/brain/awm234
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
A non-spatial bias favouring fixated stimuli revealed in patients with spatial neglect
1Division of Neurorehabilitation, University Hospital Geneva, 1211 Geneva 14 and 2Department of Neurology, University Hospital Bern, 3000 Bern, Switzerland
Correspondence to:
Dr Radek Ptak, Division of Neurorehabilitation, University Hospital Geneva, 26, Av. de Beau-Séjour, 1211 Geneva 14, Switzerland E-mail: radek.ptak{at}hcuge.ch
The cardinal feature of spatial neglect is severely impaired exploration of the contralesional space, a failure resulting in unawareness of many contralesional stimuli. This deficit is exacerbated by a reflexive attentional bias toward ipsilesional items. Here we show that, in addition to these spatially lateralized failures, neglect patients also exhibit a severe bias favouring stimuli presented at fixation. We tested neglect patients and matched healthy and right-hemisphere damaged patients without neglect in a task requiring saccade execution to targets in the left or right hemifield. Targets were presented alone or simultaneously with a distracter that appeared in the same hemifield, in the opposite hemifield, or at fixation. We found two fundamental biases in saccade initiation of neglect patients: irrelevant distracters presented in the preserved hemifield tended to capture gaze reflexively, resulting in a large number of saccades erroneously directed toward the distracter. Additionally, distracters presented at fixation severely disrupted saccade initiation irrespective of saccade direction, leading to disproportionately increased latencies of left and right saccades. This latency increase was specific to oculomotor responses of neglect patients and was not observed when a manual response was required. These results show that, in addition to their failure to inhibit reflexive glances toward ipsilesional items neglect patients exhibit a strong oculomotor bias favouring fixated stimuli. We conclude that impaired initiation of saccades in any direction contributes to the deficits of spatial exploration that characterize spatial neglect.
Key Words: visuospatial neglect; saccadic eye movements; visual attention; oculomotor function; parietal lobe
Abbreviations: ANOVA, Analysis of variance; RH, right hemisphere; RT, reaction time
Received April 10, 2007. Revised June 4, 2007. Accepted August 30, 2007.