Visual attention and the apprehension of spatial relations: The case of depth

Several studies have shown that targets defined on the basis of the spatial relations between objects yield highly inefficient visual search performan ce (e.g., Logan, 1994; Palmer, 1994), suggesting that the apprehension of s patial relations may require the selective allocation of attention within t he scene. In the present study, we tested the hypothesis that depth relatio ns might be different in this regard and might support efficient visual sea rch. This hypothesis was based, in part, on the fact that many perceptual o rganization processes that are believed to occur early and in parallel, suc h as figure-ground segregation and perceptual completion, seem to depend on the assignment of depth relations. Despite this, however, using increasing ly salient cues to depth (Experiments 2-4) and including a separate test of the sufficiency of the most salient depth cue used (Experiment 5), no evid ence was found to indicate that search for a target defined by depth relati ons is any different than search for a target defined by other types of spa tial relations, with regard to efficiency of search. These findings are dis cussed within the context of the larger literature on early processing of t hree-dimensional characteristics of visual scenes.