Fellrath Julia, Blanche-Durbec Vanessa, Schnider Armin, Jacquemoud Anne-Sophie, Ptak Radek
Division of Neurorehabilitation, University Hospitals Geneva Geneva, Switzerland.
Front Hum Neurosci. 2012 Apr 18;6:93. doi: 10.3389/fnhum.2012.00093. eCollection 2012.
Impaired visual search is a hallmark of spatial neglect. When searching for an unique feature (e.g., color) neglect patients often show only slight visual field asymmetries. In contrast, when the target is defined by a combination of features (e.g., color and form) they exhibit a severe deficit of contralesional search. This finding suggests a selective impairment of the serial deployment of spatial attention. Here, we examined this deficit with a preview paradigm. Neglect patients searched for a target defined by the conjunction of shape and color, presented together with varying numbers of distracters. The presentation time was varied such that on some trials participants previewed the target together with same-shape/different-color distracters, for 300 or 600 ms prior to the appearance of additional different-shape/same-color distracters. On the remaining trials the target and all distracters were shown simultaneously. Healthy participants exhibited a serial search strategy only when all items were presented simultaneously, whereas in both preview conditions a pop-out effect was observed. Neglect patients showed a similar pattern when the target was presented in the right hemifield. In contrast, when searching for a target in the left hemifield they showed serial search in the no-preview condition, as well as with a preview of 300 ms, and partly even at 600 ms. A control experiment suggested that the failure to fully benefit from item preview was probably independent of accurate perception of time. Our results, when viewed in the context of existing literature, lead us to conclude that the visual search deficit in neglect reflects two additive factors: a biased representation of attentional priority in favor of ipsilesional information and exaggerated capture of attention by ipsilesional abrupt onsets.
视觉搜索受损是空间忽视的一个标志。在搜索独特特征（如颜色）时，忽视患者通常仅表现出轻微的视野不对称。相比之下，当目标由多种特征组合定义（如颜色和形状）时，他们在对侧视野搜索中表现出严重缺陷。这一发现表明空间注意的序列部署存在选择性损伤。在此，我们用一种预览范式研究了这一缺陷。忽视患者搜索由形状和颜色组合定义的目标，同时呈现不同数量的干扰项。呈现时间有所变化，在某些试验中，参与者在出现其他不同形状/相同颜色的干扰项之前，先与相同形状/不同颜色的干扰项一起预览目标300或600毫秒。在其余试验中，目标和所有干扰项同时呈现。健康参与者仅在所有项目同时呈现时才表现出序列搜索策略，而在两种预览条件下均观察到弹出效应。当目标出现在右半视野时，忽视患者表现出类似模式。相比之下，当在左半视野搜索目标时他们在无预览条件下以及300毫秒预览时表现出序列搜索，甚至在600毫秒预览时部分也是如此。一项对照实验表明，未能充分从项目预览中获益可能与对时间的准确感知无关。结合现有文献来看，我们的结果使我们得出结论，忽视中的视觉搜索缺陷反映了两个相加因素：注意力优先级偏向患侧信息的表征，以及患侧突然出现的刺激对注意力的过度吸引。
