Doctor of Philosophy (PhD)



Document Type



It is well known that target prevalence impacts various cognitive processes. In visual search, rare search targets are more difficult to detect than common targets. The present research investigated novel questions about target prevalence, focusing on observers’ functional viewing field (FVF) during passive search tasks. The FVF is the area in a display where attention is focused and item processing is enhanced. According the FVF framework (Hulleman & Olivers, 2017), the size of the FVF is modulated by the ease of target detections, such that visual search involving difficult target detection reduces the FVF. Although this would suggest that low target prevalence searches should be conducted with a “narrow” FVF, recent evidence from eye-movement analyses (Papesh & Guevara Pinto, 2019) seems to indicate the opposite: Relative to high-prevalence conditions, low-prevalence search yields a wider FVF. It is possible that this effect is due to expectations of target frequency learned during high target prevalence conditions. Three experiments were conducted to test hypotheses regarding the interaction of target prevalence and target expectations in modulating the FVF. Using a dual-task paradigm, where observers passively searched for targets at center of the display while simultaneously processing probes in their periphery, Experiment 1 examined the effects of target prevalence on the FVF size. Experiment 2 manipulated observers’ trial-by-trial expectations about target presence, revealing the consequences of expectations for the FVF in isolation from effects of target prevalence. Lastly, Experiment 3 directly contrasted prevalence and expectations within the same experimental design. The results showed that the size of FVF is modulated by direct experiences (i.e., target prevalence) and externally generated expectations (i.e., trial-by-trial cues), but the interaction between the two remains unclear. The implications of these findings expand our theoretical understanding of how target prevalence influence search behaviors, particularly those that extend beyond search miss rates.



Committee Chair

Papesh, Megan

Available for download on Wednesday, March 10, 2021