EEG Evidence for Spatial Selectivity in Feature-Based Preparation for Visual Search, 2023-2024

In many visual search tasks, the detection of target objects in visual search requires feature-selective attentional guidance and space-based attentional selection. Feature-based attention is often assumed to operate in a spatially global fashion across the entire visual field, but there is also evidence that it can be restricted to task-relevant locations under some conditions. Here, we investigated whether such spatial filtering processes are already evident when representations of target-defining features (attentional templates) are activated during the preparation for an upcoming search episode. We measured N2pc components (an electrophysiological index of attentional allocation) in response to a rapid series of lateral task-irrelevant but template-matching colour probes that appeared while participants prepared for an upcoming search task with colour-defined targets. Critically, search targets would either always appear in the same lateral regions of visual space as the probes, or at different locations (near fixation or in lateral areas that never contained probes), thus rendering the probed locations either task-relevant or irrelevant. N2pc components triggered by target-colour probes during the preparation period emerged later and were attenuated when probes were presented at irrelevant locations. This demonstrates that the effects of preparatory feature-based attentional templates can be modulated by spatial expectations. However, this type of spatial filtering during search preparation only attenuates but not completely eliminates feature-based attentional modulations.

在诸多视觉搜索任务中，目标物体的侦测需要依托特征选择性注意导向与基于空间的注意选择机制。尽管通常认为基于特征的注意会在整个视野范围内以空间全域的方式运作，但也有证据表明，在特定条件下该注意机制可被限制于与任务相关的位置。本研究旨在探究：当被试为即将开展的搜索任务做准备，激活目标定义特征的表征（注意模板，attentional templates）时，此类空间过滤过程是否已然显现。实验中，我们测量了N2pc成分（注意分配的电生理指标）对一系列快速呈现的侧向探针的响应：这些探针与当前任务无关，但匹配注意模板的颜色，且呈现在被试为颜色定义目标的搜索任务做准备的时段。关键实验设置为：搜索目标要么始终与探针处于视觉空间的同一侧向区域，要么位于不同位置（靠近注视点，或是从未出现过探针的侧向区域），由此令探针探测的位置要么与任务相关，要么无关。研究结果显示，准备阶段由目标颜色探针触发的N2pc成分，在探针呈现在无关位置时，其出现时间延迟且幅值减弱。这表明，搜索准备阶段基于特征的注意模板的效应可被空间预期所调节。不过，此类搜索准备阶段的空间过滤仅能减弱而非完全消除基于特征的注意调节效应。