Task efficiency mediates the effects of movement in visual search

Intrigued by contradictory findings in the literature, we examined whether smooth motion of items in visual search displays influences search behaviour. Subjects searched for a target in two display types: static (stationary elements) or moving (elements smoothly translating in random directions at 10 deg sÿ1 ). A target was always present, and on each trial subjects responded twice: firstly to indicate that they had found this target, at which point all elements were masked and the reaction time recorded; secondly to identify the target's location. Stimuli were varied across blocks to manipulate search efficiency, as reflected by the slope of the static search functions. For very efficient and very inefficient search, neither reaction times nor performance differed between the static and moving conditions. In the middle range of efficiency, however, motion increased reaction times and decreased performance. We suggest that a ceiling effect obtains for highly efficient search, and this accounts for the absence of any difference in performance and reaction times between the static and moving conditions.Why a difference between static and motion conditions is restricted to an intermediate range of search efficiency remains unclear, but