People perform a remarkable range of tasks that require search of the visual environment for a target item among distractors. The Guided Search model (Wolfe, 1994(Wolfe, , 2007, or GS, is perhaps the best developed psychological account of human visual search. To prioritize search, GS assigns saliency to locations in the visual field. Saliency is a linear combination of activations from retinotopic maps representing primitive visual features. GS includes heuristics for setting the gain coefficient associated with each map. Variants of GS have formalized the notion of optimization as a principle of attentional control (e.g., Baldwin & Mozer, 2006;Cave, 1999;Navalpakkam & Itti, 2006;Rao et al., 2002), but every GS-like model must be 'dumbed down' to match human data, e.g., by corrupting the saliency map with noise and by imposing arbitrary restrictions on gain modulation. We propose a principled probabilistic formulation of GS, called Experience-Guided Search (EGS), based on a generative model of the environment that makes three claims: (1) Feature detectors produce Poisson spike trains whose rates are conditioned on feature type and whether the feature belongs to a target or distractor; (2) the environment and/or task is nonstationary and can change over a sequence of trials; and (3) a prior specifies that features are more likely to be present for target than for distractors. Through experience, EGS infers latent environment variables that determine the gains for guiding search. Control is thus cast as probabilistic inference, not optimization. We show that EGS can replicate a range of human data from visual search, including data that GS does not address.

Four groups of children and one group of adults judged the sizes of pairs of circles in two-and three-dimensional (2-D and 3-D) displays under restricted cue conditions. The cue of vertical intersection was either included or excluded. It was found that size constancy in the 3-D display already exists by age 4 yr. and develops further between the ages of 6 to 10 yr. No size constancy, nor differences in the judged location of the circles, was found in the 2-D condition. The cue to vertical intersection had some influence on young children's judgments in the 3-D condition, and strongly affected adults' judgments in the 2-D condition.