Natural image clutter degrades overt search performance independently of set size.

Although studies of visual search have repeatedly demonstrated that visual clutter impairs search performance in natural scenes, these studies have not attempted to disentangle the effects of search set size from those of clutter per se. Here, we investigate the effect of natural image clutter on performance in an overt search for categorical targets when the search set size is controlled. Observers completed a search task that required detecting and localizing common objects in a set of natural images. The images were sorted into high- and low-clutter conditions based on the clutter metric by Bravo and Farid (2008). The search set size was varied independently by fixing the number and positions of potential targets across set size conditions within a block of trials. Within each fixed set size condition, search times increased as a function of increasing clutter, suggesting that clutter degrades overt search performance independently of set size.