Highly dangerous road hazards are not immune from the low prevalence effect

Reducing the low prevalence effect: Does similarity search translate to binary decisions?

In visual search, observers often miss rare targets. This low prevalence effect (LPE) is resistant to many cognitive interventions. However, a recent study showed that having participants identify the item that was most similar to the target (similarity search) eliminated the LPE. As real-world searches often require binary decisions (e.g., is there a threat in this bag?) we tested whether the benefits of similarity search generalize to binary decisions and to more naturalistic stimuli. Participants searched for T shapes amongst near-T distractors and the prevalence of true Ts was manipulated. In the similarity-search-only condition, participants clicked on the "most T-like object." In the similarity search & binary decision condition, participants additionally reported whether the chosen item was a true T (yes/no). We found that in some circumstances, similarity search can be used to attenuate the LPE. However, there was an LPE for the binary decision task. Participants were less likely to classify the target as a true T during low prevalence compared with high. We replicated this result in an additional experiment using more naturalistic stimuli. Participants watched clips of road videos and clicked on the "most hazardous location" in the video, followed by a binary decision ("would you need to respond to that hazard? yes/no"). Though participants located the hazards regardless of prevalence, there was an LPE for the binary decision task. Together, these results indicate potential limitations in applying similarity search outside the laboratory; the LPE is still seen in these searches if a binary decision is involved.

No evidence of attentional prioritization for threatening targets in visual search

Throughout human evolutionary history, snakes have been associated with danger and threat. Research has shown that snakes are prioritized by our attentional system, despite many of us rarely encountering them in our daily lives. We conducted two high-powered, pre-registered experiments (total N = 224) manipulating target prevalence to understand this heightened prioritization of threatening targets. Target prevalence refers to the proportion of trials wherein a target is presented; reductions in prevalence consistently reduce the likelihood that targets will be found. We reasoned that snake targets in visual search should experience weaker effects of low target prevalence compared to non-threatening targets (rabbits) because they should be prioritized by searchers despite appearing rarely. In both experiments, we found evidence of classic prevalence effects but (contrasting prior work) we also found that search for threatening targets was slower and less accurate than for nonthreatening targets. This surprising result is possibly due to methodological issues common in prior studies, including comparatively smaller sample sizes, fewer trials, and a tendency to exclusively examine conditions of relatively high prevalence. Our findings call into question accounts of threat prioritization and suggest that prior attention findings may be constrained to a narrow range of circumstances.