Salience matters: Distractors may, or may not, speed target-absent searches

Cue relevance drives early quitting in visual search

Irrelevant salient distractors can trigger early quitting in visual search, causing observers to miss targets they might otherwise find. Here, we asked whether task-relevant salient cues can produce a similar early quitting effect on the subset of trials where those cues fail to highlight the target. We presented participants with a difficult visual search task and used two cueing conditions. In the high-predictive condition, a salient cue in the form of a red circle highlighted the target most of the time a target was present. In the low-predictive condition, the cue was far less accurate and did not reliably predict the target (i.e., the cue was often a false positive). These were contrasted against a control condition in which no cues were presented. In the high-predictive condition, we found clear evidence of early quitting on trials where the cue was a false positive, as evidenced by both increased miss errors and shorter response times on target absent trials. No such effects were observed with low-predictive cues. Together, these results suggest that salient cues which are false positives can trigger early quitting, though perhaps only when the cues have a high-predictive value. These results have implications for real-world searches, such as medical image screening, where salient cues (referred to as computer-aided detection or CAD) may be used to highlight potentially relevant areas of images but are sometimes inaccurate.

The effect of prevalence on distractor speeded search termination

Visual search can be disrupted by irrelevant salient stimuli. Recently, Moher (Psychological Science, 31(1), 31-42, 2020) found salient distractors to speed search when a target was absent and increase error rates when the target was present. That is, distractors lowered search-quitting thresholds. Nonetheless, the salient distractors Moher used were present on 50% of all trials. Since distractor prevalence has been found to influence search processes more broadly, here, we aimed to test the effect of distractor prevalence on this distractor-quitting threshold effect (QTE). To do so, we conducted two experiments. Experiment 1 compared the performance of individuals in a search task where the target was present on 50% of trials across two distractor-prevalence conditions (25% vs. 75% prevalence). Experiment 2 followed the same procedure, except with a wider probability margin (10% vs. 90% prevalence). In Experiment 1, distractor prevalence did not modulate the QTE. Critically, in Experiment 2, the QTE was modulated. For high-prevalence distractors (90%), a QTE was observed. However, as low-prevalence distractors (10%) did not speed search, no QTE was observed. One potential reason no QTE was observed was because low-prevalence distractors have significantly greater attentional capture, which washed out speeded termination effects.

Investigating the role of spatial filtering on distractor suppression

In recent years, evidence has accumulated towards a distractor suppression mechanism that enables efficient selection of targets in a visual search task. According to these findings, the search for a target is faster in the presence of a salient distractor in a display among homogenous distractors as opposed to its absence. Studies have also shown that distractor suppression not only operates on the feature level but can also be spatially guided. The motivation of the current study was to examine if spatially guided distractor suppression can be goal-driven. We tested this across four experiments. In Experiment 1A, the task was to search for a shape target (e.g., a circle) and discriminate the orientation of the line within it. In some trials, a salient color distractor was presented in the display while participants were told that it appeared in one of the two locations on the horizontal axis (or the vertical axis, counterbalanced across participants). We expected enhanced distractor suppression when the salient distractor appeared within this "spatial filter" but did not find it since the target was also presented at the filtered locations. Experiment 1B replicated Experiment 1A, except that the target was always presented outside the filter; filtering enhanced search performance. In Experiment 2 even when the filter contained the salient distractor in only 65% of the filtered trials, filtering benefited search performance. In Experiment 3, the filter changed on every trial and did not benefit suppression.

Emphasizing responder speed or accuracy modulates but does not abolish the distractor-induced quitting effect in visual search

When a highly salient distractor is present in a search array, it speeds target absent visual search and increases errors during target present visual search, suggesting lowered quitting thresholds (Moher in Psychol Sci 31(1):31-42, 2020). Missing a critical target in the presence of a highly salient distractor can have dire consequences in real-world search tasks where accurate target detection is crucial, such as baggage screening. As such, the current study examined whether emphasizing either accuracy or speed would eliminate the distractor-generated quitting threshold effect (QTE). Three blocks of a target detection search task which included a highly salient distractor on half of all trials were used. In one block, participants received no instructions or feedback regarding performance. In the remaining two blocks, they received instructions and trial-by-trial feedback that either emphasized response speed or response accuracy. Overall, the distractor lowered quitting thresholds, regardless of whether response speed or response accuracy was emphasized in a block of trials. However, the effect of the distractor on target misses was smaller when accuracy was emphasized. It, therefore, appears that while the distractor QTE is not easily eradicated by explicit instructions and feedback, it can be shifted. As such, future research should examine the applicability of these and similar strategies in real-world search scenarios.

Delayed onsets are not necessary for generating distractor quitting thresholds effects in visual search

Salient distractors lower quitting thresholds in visual search. That is, when searching for the presence of a target among filler items, a large heterogeneously coloured distractor presented at a delayed onset produces quick target-absent judgements and increased target-present errors. The aim of the current study was to explore if the timing of the salient distractor modulates this Quitting Threshold Effect (QTE). In Experiment 1, participants completed a target detection search task in the presence or absence of a salient singleton distractor that either appeared simultaneously with other search items or appeared at a delayed onset (i.e., 100 ms or 250 ms after other array items appeared). In Experiment 2, a similar method was used, except that the salient singleton distractor appeared simultaneously, 100 ms before, or 100 ms after the other array items. Across both experiments, we observed robust distractor QTEs. Regardless of their onset, salient distractors decreased target-absent search speeds and increased target-present error rates. In all, the present findings suggest that delayed onsets are not required for lowered quitting thresholds in visual search.

The presence of a distractor matching the content of working memory induces delayed quitting in visual search

Previous research has shown that the presence of a distractor object matching the current content of working memory interacts with visual search. Because finding a target and quitting a search without finding a target may be implemented by qualitatively different processes, it is possible that the effects of a memory-matching distractor on target-present trials and on target-absent trials reveal different mechanisms by which the memory-matching distractor interacts with visual search. Although previous studies have well established the effect of attentional capture by a memory-matching distractor when the target object is found in the search display, there remains an open question about whether the presence of a memory-matching distractor can affect the process of search termination when no target is found. In the present study, we showed that search termination times on target-absent trials were delayed by the presence of a distractor matching the content of visual working memory. This delayed quitting effect cannot be conceived of as a more general influence of visual short-term memory, because the presence of a distractor matching the content of passive visual short-term memory (i.e., visual priming) did not influence quitting behavior in visual search. These findings offer a novel perspective that distractors matching the information maintained in visual working memory can cause observers to delay search termination when no target has been found.