Modulating the attentional bias in unilateral neglect: the effects of the strategic set |
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Authors: | Paolo Bartolomeo Eric Siéroff Caroline Decaix Sylvie Chokron |
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Institution: | (1) INSERM Unit 324, Centre Paul Broca, 2ter rue d'Alésia, 75014 Paris, France,;(2) Neuroscience Department, Henri-Mondor Hospital, Créteil, France,;(3) Université René Descartes (Paris 5), Laboratoire de Psychologie Expérimentale, CNRS URA 8581, Paris, France,;(4) Laboratoire de Psychologie Expérimentale, CNRS UMR 5105, Grenoble, France,;(5) Fondation Ophtalmologique Rothschild, Paris, France, |
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Abstract: | Left unilateral neglect is a neurological condition characterized by an impairment in orienting and responding to events
occurring on the left side. To gain insight into the brain mechanisms of space processing and to provide theoretical foundations
for patient rehabilitation, it is important to explore the attentional bias shown by neglect patients in the light of existing
models of normal attentional orienting. Three experiments tested the hypothesis that attentional bias in neglect involves
primarily exogenous, or stimulus-based, orienting of attention, with relatively preserved endogenous, or voluntary, orienting.
Six patients with right hemisphere damage and left unilateral neglect and 18 age-matched participants without brain damage
performed a cued reaction time (RT) task to targets which could appear in one of two lateral boxes. Cues consisted of a brief
brightening of the contour of one of the boxes. The target followed the cue at 150, 550, or 1000 ms stimulus-onset asynchrony
(SOA). In experiment 1, the cues were not informative about the future location of the target, and thus elicited a purely
exogenous orienting of attention. Controls showed slowed RTs to the cued locations at SOAs > 150 ms, consistent with the notion
of inhibition of return (IOR). Neglect patients had no evidence of IOR for right targets; they showed a disproportionate cost
for left targets preceded by right (invalid) cues; this cost was maximal at the shortest SOA, consistent with the idea of
a biased exogenous orienting in neglect. In experiment 2, 80% of the cues were valid (i.e., they correctly predicted the location
of the impending target), thus inducing an initially exogenous, and later endogenous, attentional shift toward the cued box.
Neglect patients showed again a cost for left invalidly cued targets, which this time persisted at SOAs > 150 ms, as if patients'
attention had been cued to the right side not only exogenously, but also endogenously, thus rendering more difficult an endogenous
reorienting toward the left. In experiment 3, only 20% of the cues were valid, so that the best response strategy was to endogenously
orient attention toward the box opposite to the cued one. Controls were able to take advantage of invalid cues to rapidly
respond to targets. In this condition, neglect patients were able to nullify their spatial bias; they achieved their fastest
RTs to left targets, which were in the range of their RTs to right targets. However, for neglect patients fast responses to
left targets occurred only at 1000 ms SOA, while controls were able to redirect their attention to the uncued box already
at 550 ms SOA. Altogether, these results suggest that endogenous orienting is relatively spared, if slowed, in unilateral
neglect.
Electronic Publication |
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Keywords: | Spatial attention Exogenous orienting Endogenous orienting Unilateral neglect Brain damage |
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