Department of Psychology, Ludwig-Maximilians-Universität München, D-80802 Munich, Germany.
Cereb Cortex. 2012 Jul;22(7):1554-63. doi: 10.1093/cercor/bhr231. Epub 2011 Sep 7.
Visual search for feature singletons is slowed when a task-irrelevant, but more salient distracter singleton is concurrently presented. While there is a consensus that this distracter interference effect can be influenced by internal system settings, it remains controversial at what stage of processing this influence starts to affect visual coding. Advocates of the "stimulus-driven" view maintain that the initial sweep of visual processing is entirely driven by physical stimulus attributes and that top-down settings can bias visual processing only after selection of the most salient item. By contrast, opponents argue that top-down expectancies can alter the initial selection priority, so that focal attention is "not automatically" shifted to the location exhibiting the highest feature contrast. To precisely trace the allocation of focal attention, we analyzed the Posterior-Contralateral-Negativity (PCN) in a task in which the likelihood (expectancy) with which a distracter occurred was systematically varied. Our results show that both high (vs. low) distracter expectancy and experiencing a distracter on the previous trial speed up the timing of the target-elicited PCN. Importantly, there was no distracter-elicited PCN, indicating that participants did not shift attention to the distracter before selecting the target. This pattern unambiguously demonstrates that preattentive vision is top-down modifiable.
当任务不相关但更突出的分散注意力的单一元素同时呈现时，对特征单一元素的视觉搜索会变慢。虽然人们一致认为这种分散注意力的干扰效应可以受到内部系统设置的影响，但在处理的哪个阶段开始影响视觉编码仍存在争议。“受刺激驱动”观点的支持者认为，视觉处理的初始扫视完全由物理刺激属性驱动，只有在选择最突出的项目后，自上而下的设置才能影响视觉处理。相比之下，反对者认为自上而下的期望可以改变初始选择优先级，从而使焦点注意力“不是自动”转移到表现出最高特征对比的位置。为了准确追踪焦点注意力的分配，我们在一项任务中分析了后对侧负波（PCN），在该任务中，分散注意力出现的可能性（期望）被系统地改变。我们的结果表明，高（与低相比）分散注意力的期望和在前一个试验中经历分散注意力都会加快目标引发的 PCN 的时间。重要的是，没有分散注意力引发的 PCN，这表明参与者在选择目标之前没有将注意力转移到分散注意力上。这种模式明确表明，前注意视觉是可以自上而下进行调整的。
