Quantitative assessment of effects of visual scanning on concurrent task performance

Much of the research in visual scanning has adopted a single task experimental paradigm. The characteristics of visual scanning in multi-task situations are largely unknown. A quantitative assessment of the effects of visual scanning on concurrent task performance was gained from two experiments. Subjects were required to perform a simulated driving task, which involved a primary pursuit tracking task and a discrete response task. The response task was one of simple information acquisition in the first experiment and of complex information integration in the second. The information acquisition task required subjects to search for a spatial or verbal target. The information integration task required them to search for a spatial or verbal target and then make a rule-based decision by integrating the information carried by current and previous targets. The two types of task involved either spatial or verbal material, whose location was displayed with 4 levels of spatial uncertainty. The results of the two experiments which were: 2 (single/dual task) x 2 (spatial/verbal material) x 4 (levels of uncertainty of target location) revealed unique characteristics of visual scanning in multi-task performance. The effects of visual scanning on task performance and subjective workload were more pronounced in the dual task conditions than in the single. Increases in scanning demand produced greater interference with a concurrent spatial task than with a verbal one when the location uncertainty of visual scanning was sufficiently high. Implications for multi-task human-machine interface design are discussed.