Scanning behaviour in natural scenes is influenced by a preceding unrelated visual search task

Three experiments explored the transference of visual scanning behaviour between two unrelated tasks. Participants first viewed letters presented horizontally, vertically, or as a random array. They then viewed still images (experiments 1 and 2) or video clips (experiment 3) of driving scenes, under varying task conditions. Despite having no relevance to the driving images, layout of stimuli in the letter task influenced scanning behaviour in this subsequent task. In the still images, a vertical letter search increased vertical scanning, and in the dynamic clips, a horizontal letter search decreased vertical scanning. This indicated that (i) models of scanning behaviour should account for the influence of a preceding unrelated task; (ii) carry-over is modulated by demand in the current task; and (iii) in situations where particular scanning strategies are important for primary task performance (eg driving safety), secondary task information should be displayed in a manner likely to produce a congruent scanning strategy.