Bartolomeo P, Siéroff E, Decaix C, Chokron S
INSERM Unit 324, Centre Paul Broca, 2ter rue d'Alésia, 75014 Paris, France.
Exp Brain Res. 2001 Apr;137(3-4):432-44. doi: 10.1007/s002210000642.
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.
左侧单侧忽视是一种神经病症，其特征在于在定位和响应左侧发生的事件方面存在障碍。为了深入了解空间处理的大脑机制并为患者康复提供理论基础，根据现有的正常注意力定向模型来探究忽视患者表现出的注意力偏差非常重要。三项实验检验了这样一个假设，即忽视中的注意力偏差主要涉及外源性或基于刺激的注意力定向，而内源性或自愿性定向相对保留。六名患有右半球损伤和左侧单侧忽视的患者以及18名年龄匹配的无脑损伤参与者执行了一项线索反应时任务，目标可能出现在两个横向方框中的一个。线索包括其中一个方框轮廓的短暂变亮。目标在150、550或1000毫秒的刺激起始异步（SOA）下跟随线索出现。在实验1中，线索与目标的未来位置无关，因此引发了纯粹的外源性注意力定向。对照组在SOA>150毫秒时对线索位置的反应时变慢，这与返回抑制（IOR）的概念一致。忽视患者对右侧目标没有IOR的证据；他们对右侧（无效）线索之前的左侧目标表现出不成比例的代价；这种代价在最短的SOA时最大，这与忽视中存在偏向性外源性定向的观点一致。在实验2中，80%的线索是有效的（即它们正确预测即将出现的目标的位置），从而引发了最初的外源性和后来的内源性注意力向线索方框的转移。忽视患者再次对左侧无效线索的目标表现出代价，这次在SOA>150毫秒时仍然存在，就好像患者的注意力不仅在外源性上，而且在内源性上都被引导到了右侧，从而使向内源性地重新定向到左侧变得更加困难。在实验3中，只有20%的线索是有效的，因此最佳的反应策略是内源性地将注意力定向到与线索方框相对的方框。对照组能够利用无效线索快速对目标做出反应。在这种情况下，忽视患者能够消除他们的空间偏差；他们对左侧目标的反应时最快，处于他们对右侧目标的反应时范围内。然而，对于忽视患者来说，对左侧目标的快速反应仅在1000毫秒的SOA时出现，而对照组在550毫秒的SOA时就能够将注意力重新定向到未提示的方框。总之，这些结果表明，在单侧忽视中，内源性定向相对保留，只是速度变慢。
