The University of Queensland, Queensland Brain Institute, St Lucia 4072, Australia, and The University of Queensland, School of Psychology, St Lucia 4072, Australia.
J Neurosci. 2014 Feb 26;34(9):3390-401. doi: 10.1523/JNEUROSCI.3630-13.2014.
The visual world is typically too complex to permit full apprehension of its content from a single fixation. Humans therefore use visual search to direct attention and eye movements to locations or objects of interest in cluttered scenes. Psychophysical investigations have revealed that observers can select target elements from within an array of distractors on the basis of their spatial location or simple features, such as color. It remains unclear, however, how stimuli that lie outside the current search array are represented in the visual system. To investigate this, we recorded continuous neural activity using EEG while participants searched a foveal array of colored targets and distractors, and ignored irrelevant objects in the periphery. Search targets were defined either by a unique feature within the array or by a conjunction of features. Objects outside the array could match the target or distractor color within the array, or otherwise possessed a baseline (neutral) color present only in the periphery. The search array and irrelevant peripheral objects flickered at unique rates and thus evoked distinct frequency-tagged neural oscillations. During conjunction but not unique-feature search, target-colored objects outside the array evoked enhanced activity relative to distractor-colored and neutral objects. The results suggest that feature-based selection applies to stimuli at ignored peripheral locations, but only when central targets compete with distractors within the array. Distractor-colored and neutral objects evoked equivalent oscillatory responses, suggesting that feature-based selection at ignored locations during visual search arises exclusively from enhancement rather than suppression of neural activity.
视觉世界通常过于复杂，以至于无法从单次注视中完全理解其内容。因此，人类使用视觉搜索来引导注意力和眼球运动，以关注杂乱场景中的目标位置或物体。心理物理学研究表明，观察者可以根据目标的空间位置或颜色等简单特征从数组中的干扰项中选择目标元素。然而，目前尚不清楚视觉系统如何表示当前搜索数组之外的刺激。为了研究这个问题，我们使用 EEG 记录了参与者在注视彩色目标和干扰项的数组中进行搜索时的连续神经活动，同时忽略了外围的不相关物体。搜索目标可以通过数组内的独特特征或特征的组合来定义。数组外的物体可以与数组内的目标或干扰项颜色匹配，或者具有仅存在于外围的基线（中性）颜色。搜索数组和不相关的外围物体以独特的频率闪烁，从而引发了不同的频率标记神经振荡。在结合搜索但不是独特特征搜索时，数组外的目标颜色物体相对于干扰项颜色和中性物体引起了增强的活动。结果表明，基于特征的选择适用于被忽略的外围位置的刺激，但仅当中央目标与数组中的干扰项竞争时才适用。干扰项颜色和中性物体引起了等效的振荡反应，这表明在视觉搜索期间，基于特征的忽略位置选择仅来自于神经活动的增强而不是抑制。
