Manipulating Processing Biases to Mitigate the Low Prevalence Effect

When searching for rare items, targets are missed at a much higher rate than when they are more commonly encountered, this is known as the low prevalence effect (LPE; Wolfe et al., 2005). Previous research has been unsuccessful in eliminating this effect, even when explicitly warning participants about the effect (Wolfe et al., 2007). In this investigation, we attempted to implicitly manipulate participants' processing bias by using the Navon task (Navon, 1977). In the Navon task, participants are instructed to indicate the parity of either a larger or smaller number. As the LPE is characterized by short search times and fewer fixations (Godwin et al., 2015; Peltier & Becker, 2016), we hypothesized that a perceptual bias task may implicitly reduce it by increasing the number of fixations. We predicted that a local processing bias would increase fixations, increase search times, and therefore increase accuracy rates and mitigate LPE. Comparatively, this same task can also induce a global processing bias, which should exacerbate the LPE. Participants completed a Ts/Ls search with target prevalence manipulated between subjects (20% v 80% target-present). The search task was intermixed with Navon trials during each block to ensure participants could not predict whether a search or a Navon trial would appear next, inducing an implicit perceptual bias. The type of perceptual bias (local v global v control) was manipulated within subjects across three blocks of trials. The results replicate the traditional LPE regarding search hits, search times, and fixation counts, with no Prevalence x Type of Bias interaction across any measure. However, we observed a significant main effect of Type of Bias for fixation count, indicating that local processing bias did increase the number of fixations, relative to a global bias. This finding is promising as it suggests that perceptual biases can implicitly influence search behaviors.