Abstract
Vigilance and visual search tasks have been two important tasks used in visual attention research. Both tasks involve detection of a potential target. While vigilance tasks usually involve continuous monitoring of a single object, visual search tasks usually involve multiple objects and discrete trials. In real life, we often search for potential targets among multiple objects continuously. Infrared body temperature surveillance and lifeguarding are some examples. In this study, we are interested in whether previous findings on visual search generalize to a continuous variant. Specifically, we want to know whether a target prevalence effect – that targets are usually missed when they are rare – generalizes to continuous visual search. We designed a task that involves detection of a target feature among objects of continuously changing features. Targets may occur rarely or frequently in each several minute long session that is not separated into trials. In Experiment 1, participants monitored for the occurrence of a specific color among changing colors. Rare targets were associated with a slower detection RT and a higher miss rate. In Experiment 2, participants monitored both for a color and an orientation, and their relative frequency was manipulated. For both features, miss rates were higher when they were rarer. In Experiment 3, set size effects were measured and showed a relative frequency effect. The more frequent targets were associated with higher search efficiencies. Experiment 4 ruled out a vigilance account based on a flash detection dual task. This suggests that target-rate effects in continuous visual search were mostly decisional. Taken together, common behavioral effects in visual search, including target-rate effects and set-size effects, seems to be replicable in its continuous variant. Further research is needed to detail the similarities and differences in the attentional and decisional processes between standard and continuous visual search tasks.