Abstract
In visual search, infrequent targets are missed more often than common ones; this phenomenon is known as the Low Prevalence Effect (LPE; Van Wert & Wolfe, 2010; Horowitz, 2017). Various studies have demonstrated the incredible difficulty in mitigating this effect (e.g., Van Wert, et al., 2009; Wolfe et al., 2007). Here, we attempted to module the size of the LPE by biasing observers’ attentional “spread” during a basic visual search task. Specifically, because one of the hallmarks of the LPE involves fewer fixations and shorter target-absent RTs during low, relative to high, prevalence conditions (Godwin et al., 2015; Peltier & Becker, 2016), we predicted that by biasing a local processing approach we would increase RTs and the number of item fixations made during search (Wen & Kawabata, 2018), consequently decreasing miss rates. Comparatively, a global processing bias would produce the opposite effect and exacerbate the LPE. To do so, we used a number-parity version of the Navon Task (Navon, 1977) to bias a global or local spread of attention prior to two blocks of standard T’s and L’s searches in which targets had a high chance (80%) or a low chance (20%) of being present (order counterbalanced). A control group completed a lexical-decision task prior to search. The results showed that, overall, we replicated the LPE: Observers missed more targets, spent less time searching, and made fewer fixation in the low, relative to high, prevalence condition. In terms of miss rates, however, we did not reliably mitigate it in the local bias condition relative to the control group. Despite this, the global bias condition did trend towards a larger LPE, as predicted, with shorter RTs and fewer fixations made during target-absent trials in relation to the control group, suggesting that the “spread” of attention during search may modulate target-prevalence effects.