Eye movements reveal two search modes for the detection of targets in novel dynamically changing visual displays

摘要

Standard visual search tasks present participants with objects that do not change. This contrasts with some real-world tasks where observers monitor complex displays of dynamically changing visual indicators over time for evidence of risk (e.g. warning lights turning red). In these tasks, target detection may be driven by responses to specific target onsets, or by monitoring changes to potential targets over time. In the present study, participants completed a novel dynamic visual search task. Arrays of 9x12 squares changed between 16 colours at varying rates and each trial lasted 40 seconds. Participantsa?? task was to respond with mouse-clicks after moving a cursor to targets defined by a specific colour. Only a single target was ever present at once and target prevalence, the proportion of target-present trials, was either low (6%) or high (66%). Eye movements provided evidence for two concurrent modes of search. 46% of targets were detected in accordance with responses to specific target onsets, but other targets were detected predictively, via monitoring of distractors with likelihood to become targets. Monitoring might operate through a coarse template in which squares within two colour-steps of the target are assessed as potential targets. Hit-rate did not differ between high (84%) and low (82%) prevalence and, most often, targets were missed because they were not fixated. However, in line with recent evidence, target detection was slower when prevalence was low (2900ms) versus high (2500ms) and this was due extended verification times (time from first target fixation to response). We conclude that (1) target prevalence effects are similar in dynamic search to those in standard search; (2) prevalence influences search in dynamic displays by slowing verification; and (3) there are two distinct modes of search for targets in dynamically changing displays. Further analyses will explore the relationships between prevalence and search mode.