Salience-Based Selection: Attentional Capture by Distractors Less Salient Than the Target

Current accounts of attentional capture predict the most salient stimulus to be invariably selected first. However, existing salience and visual search models assume noise in the map computation or selection process. Consequently, they predict the first selection to be stochastically dependent on salience, implying that attention could even be captured first by the second most salient (instead of the most salient) stimulus in the field. Yet, capture by less salient distractors has not been reported and salience-based selection accounts claim that the distractor has to be more salient in order to capture attention. We tested this prediction using an empirical and modeling approach of the visual search distractor paradigm. For the empirical part, we manipulated salience of target and distractor parametrically and measured reaction time interference when a distractor was present compared to absent. Reaction time interference was strongly correlated with distractor salience relative to the target. Moreover, even distractors less salient than the target captured attention, as measured by reaction time interference and oculomotor capture. In the modeling part, we simulated first selection in the distractor paradigm using behavioral measures of salience and considering the time course of selection including noise. We were able to replicate the result pattern we obtained in the empirical part. We conclude that each salience value follows a specific selection time distribution and attentional capture occurs when the selection time distributions of target and distractor overlap. Hence, selection is stochastic in nature and attentional capture occurs with a certain probability depending on relative salience.

现有注意捕获（attentional capture）理论均认为，显著性最高的刺激必然会被优先选择。然而，现有的显著性与视觉搜索模型均假设，在显著性图计算或选择过程中存在噪声干扰。因此这类模型预测，首次选择的结果会随显著性水平呈现随机依赖性，这意味着注意甚至可能优先被视野中第二显著（而非最显著）的刺激所捕获。但迄今为止尚无低显著性分心物捕获注意的相关报道，且基于显著性的选择理论主张，分心物必须具备更高的显著性才能成功捕获注意。

本研究采用视觉搜索分心物范式的实证与建模方法，对该理论预测进行了验证。实证部分中，我们通过参数化方式操纵目标与分心物的显著性水平，并对比了存在与不存在分心物时的反应时干扰效应。反应时干扰效应与分心物相对于目标的显著性水平呈显著相关。此外，通过反应时干扰与眼动捕获（oculomotor capture）指标的测量结果显示，即使显著性低于目标的分心物也能捕获注意。建模部分中，我们利用显著性的行为测量指标，并纳入包含噪声的选择时间进程，对分心物范式下的首次选择过程进行了模拟。我们成功复现了实证研究中得到的结果模式。

本研究得出结论：每个显著性值均遵循特定的选择时间分布，当目标与分心物的选择时间分布发生重叠时，便会发生注意捕获。因此，选择过程本质上具有随机性，注意捕获的发生概率取决于目标与分心物的相对显著性水平。