Search

In visual search tasks, targets are difficult to find when they are similar to the surrounding nontargets. In this scenario, it is optimal to tune attention to target features that maximize the difference between target and nontargets. We investigated whether the optimal tuning of attention is driven by biases arising from previously attended stimuli (i.e., trial history). Consistent with the effects of trial history, we found that optimal tuning was stronger when a single target–nontarget relation was repeated than when two target–nontarget relations alternated randomly. Detailed analysis of blocks with random alternation showed that optimal tuning was stronger when the target–nontarget relation probed in the current trial matched the relation in the previous trial. We evaluated several mechanisms that may underlie the effects of trial history, such as priming of attentional set, switch costs, and sensory adaptation. However, none of the accounts was able to fully account for the pattern of results. Public Significance Statement: Visual search is a common everyday activity. For instance, we often look for objects in a particular color. This task is difficult when the color of the target is similar to the surrounding colors. Observers perform surprisingly well in this situation, suggesting that they adjust attention optimally to maximize the difference between the color of the target and the surrounding colors. However, we show that this adjustment breaks down when observers attempt to find more than a single target. Therefore, to optimize performance, it may be best to search for only one object at a time. [ABSTRACT FROM AUTHOR]

In visual search tasks, negative features provide information about stimuli that can be excluded from search. It has been shown that these negative features help participants to locate the target, possibly by attentional suppression of stimuli sharing the negative feature. Attentional suppression is assumed to be reflected in an event-related potential, the PD component. To provide a further test of these assumptions, we presented the color of the distractor at the start of a trial and asked participants to find the other colored stimulus in the subsequent search display. Consistent with attentional suppression, we observed a PD to a lateral distractor shown with a vertical target. However, the PD occurred in this condition only when target and distractor could also be on opposite sides of fixation. The effect of trial context on the PD suggests that the PD reflects a search strategy whereby participants select stimuli opposite to the distractor when trials with opposite placements occur during the experiment. Therefore, the PD to the distractor may in fact be an N2pc to the opposite stimulus, indicating that the distractor is not suppressed, but avoided by redirecting attentional selection to the opposite side. [ABSTRACT FROM AUTHOR]

Attentional templates are representations of target features in working memory (WM). Although two attentional templates can guide visual search in dual-target search, search efficiency is reduced compared with one attentional template in single-target search. Here, we investigated whether the allocation of WM resources contributes to these differences. Participants always memorized two colors, but the use of the corresponding WM representations varied. In the blocked conditions, the two colors were either maintained as attentional templates for dual-target search or as simple WM representations for recall only. In the mixed condition, one color was maintained as an attentional template for single-target search and the other as a simple WM representation for recall only. Reaction times (RTs) were delayed and recall precision reduced with two attentional templates in the blocked condition compared with one attentional template in the mixed condition, indicating that search efficiency and WM resources decreased in dual-compared with single-target search. Moreover, the attentional template was always recalled more precisely than the simple WM representation in the mixed condition, despite lowered visual search frequency (Experiment 2) and retro-cueing (Experiment 3). Consistent with the existence of an "active" WM state, resources were strongly biased toward the attentional template in single-target search. In dual-target search, however, resources were balanced between two attentional templates and flexibly adjusted with retro-cues, as with two simple WM representations. Therefore, the allocation of WM resources goes beyond the traditional dichotomy between "active" and "accessory" WM states and explains how attentional templates guide visual search with variable efficiency. [ABSTRACT FROM AUTHOR]