Part of Advances in Neural Information Processing Systems 20 (NIPS 2007)
David Baldwin, Michael C. Mozer
People perform a remarkable range of tasks that require search of the visual en- vironment for a target item among distractors. The Guided Search model (Wolfe, 1994, 2007), or GS, is perhaps the best developed psychological account of hu- man 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 en- vironment 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 infer- ence, not optimization. We show that EGS can replicate a range of human data from visual search, including data that GS does not address.