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

Dimension intertrial and cueing effects in localization: support for pre-attentively weighted one-route models of saliency

There are several alternative accounts of dimensional intertrial and cueing effects in singleton feature search tasks. Some accounts assume that these effects arise at post-selective processing stages; dual-route accounts assume them to be perceptual in nature, but coming into play only in non-spatial tasks (e.g., detection but not localization). By contrast, the Dimension Weighting Account (DWA) assumes dimensional effects to arise at pre-attentive processing stages of spatial as well as non-spatial tasks. The data available are ambiguous, permitting no clear-cut choice among these accounts. Therefore, the present study examined for early effects of dimensional weighting in a spatial task, the presence of which is only predicted by the DWA and not by post-selective or dual-route accounts. Salience is known to saturate for high feature contrast and long presentation times. Consequently, with lower bottom-up salience that still permits efficient search, dimensional weights would produce a greater modulation-if present at all. Thus, we examined localization accuracy under brief-presentation conditions in Experiment 1, and localization speed under conditions of low versus high feature contrast in Experiment 2. Both experiments revealed significant dimension intertrial and cueing effects. This strongly argues against dual-route accounts and strengthens evidence for a pre-attentive origin of these effects