1Sometimes, salient-but-irrelevant objects (distractors) presented concurrently with a search 2 target cannot be ignored and attention is involuntarily allocated towards the distractor first. 3Several studies have provided electrophysiological evidence for involuntary misallocations of 4 attention towards a distractor, but much less is known about the mechanisms that are needed 5 to overcome a misallocation and re-allocate attention towards the concurrently presented 6 target. In our study, electrophysiological markers of attentional mechanisms indicate that (i) 7 the distractor captures attention before the target is attended, (ii) a misallocation of attention is 8 terminated actively (instead of attention fading passively), and (iii) the misallocation of 9 attention towards a distractor delays the attention allocation towards the target (rather than 10 just delaying some post-attentive process involved in response selection). This provides the 11 most complete demonstration, to date, of the chain of attentional mechanisms that are evoked 12 when attention is misguided and recovers from capture within a search display. 13

Because visual working memory has a very restricted capacity, good filtering mechanisms are essential for its successful functioning. A neuronal signal emitted by the prefrontal cortex is considered to be an important contributor to filtering. Proof of the functional significance of this signal during normal cognitive functioning is, however, still missing. Furthermore, research has so far neglected that the prefrontal cortex must receive input from posterior brain areas that report the necessity to filter. From human electroencephalograms, we extracted several event-related components that reflect the different subprocesses of filtering. On the basis of their timing and a clear pattern of correlations, we reason that filtering might consist of a causal chain of events that involve prefrontal and posterior cortex regions: After distractors are detected in posterior regions, a prefrontal mechanism is activated, which in turn prevents subsequent unnecessary parietal storage of distractor information.

Objects that stand out from the environment tend to be of behavioral relevance and the visual system is tuned to preferably process these salient objects by allocating focused attention. However, attention is not just passively (bottom-up) driven by stimulus features, but previous experiences and task goals exert strong biases towards attending or actively ignoring salient objects. The core and eponymous assumption of the Dimension-Weighting Account (DWA) is that these top-down biases are not as flexible as one would like them to be; rather, they are subject to dimensional constraints. In particular, DWA assumes that people can often not search for objects that have a particular feature, but only for objects that stand out from the environment (i.e., that are salient) in a particular feature dimension. We review behavioral and neuroimaging evidence for such dimensional constraints in three areas: search history, voluntary target enhancement, and distractor handling. The first two have been the focus of research on DWA since its inception and the latter the subject of our more recent research. Additionally, we discuss various challenges to the DWA and its relation to other prominent theories on top-down influences in visual search.

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The dimension-weighting account predicts that if observers search for a target standing out from the background in a particular dimension, they cannot readily ignore a distractor standing out in the same dimension. This prediction is tested here by asking two groups of observers to search for an orientation target or a luminance target, respectively, and presenting an additional distractor defined in either the respectively same dimension or the other dimension. Notably, in this cross-over design, the physically identical distractors served both as same-and different-dimension distractors, depending on target condition. While same-dimension distractors gave rise to massive interference, different-dimension distractors caused much weaker (though still substantial) interference. This result is most readily explained by the dimension-weighting account: different-dimension distractors are considerably downweighted but not fully suppressed. Furthermore, same-and different dimension distractors delayed response times even when considering only the fastest (down to 2.5%) of trials, indicating that interference is exerted consistently on each trial, rather than probabilistically on some trials. Our results put strong constraints on models of distractor handling in visual search.