Cerebral Cortex Advance Access originally published online on May 18, 2005
Cerebral Cortex 2006 16(3):337-345; doi:10.1093/cercor/bhi111
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Reflexive Orienting in Spatial Neglect Is Biased towards Behaviourally Salient Stimuli
Division of Rehabilitation, University Hospital Geneva, 1211 Geneva 14, Switzerland
Address correspondence to Dr Radek Ptak, Division of Rehabilitation, University Hospital Geneva, 26, Av. de Beau-Séjour, CH-1211 Geneva 14, Switzerland. Email: Radek.Ptak{at}hcuge.ch.
Patients with spatial neglect are impaired when detecting contralesional targets presented shortly after an ipsilesional cue. This ‘disengagement’ deficit is believed to reflect reflexive orienting towards ipsilesional stimuli that is independent of behavioural goals. Here, we show that the extent of this spatial bias depends on the behavioural salience of ipsilesional stimuli. Healthy participants, brain-injured patients without neglect and neglect patients reacted to ipsilesional and contralesional visual targets. Prior to target presentation, a visual cue similar or dissimilar to the target was presented at target position or opposite the target. Although participants did not react to the similar cue, it had high behavioural salience since it shared features with the target stimulus. Neglect patients showed dramatically increased reaction times to contralesional targets, but only when these followed behaviourally relevant ipsilesional cues. No decrease of performance was observed with irrelevant cues. This performance pattern was not due to perceptual similarity, since the same effect was found when cue and target were semantically related but differed perceptually. Importantly, semantically related cues ceased to attract attention when they were defined as behaviourally irrelevant. These results show that neglect patients only orient attention reflexively towards ipsilesional stimuli with high behavioural salience.
Key Words: behavioural salience • parietal lobe • reflexive orienting • selective attention • spatial neglect
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