Visual search of traffic scenes : on the effect of location expectations

The present study investigates top-down governed visual selection in natural traffic scenes. The subjects had to search for a target object (for example, a traffic sign, or other road users) which was embedded in a natural traffic scene. Given a particular prototypical scene, the target was located either at a likely (expected) or unlikely (unexpected) position. The probability that a target object appeared at a likely location was varied between groups of subjects. The results showed the existence of scene dependent scanning strategies: search in the unexpected condition was significantly more error prone than search in the expected condition. This suggests that subjects strategically prepare for the upcoming stimulus and only search those locations which are likely to contain a target. If the target is not found at those likely locations, subjects tend to give a negative response. This effect remained after repeated presentation. The importance of these findings for search during actual driving is discussed.