Project Summary/Abstract In the previous project period we developed and tested principled theories for identification of occluding targets and depth boundaries in noise and natural backgrounds (previous Aims 1 & 2). The current aims are directed at extending these aims, and our previous work on visual search, to the study of covert and overt visual search for additive and occluding targets. In preliminary studies, we developed a principled theory of covert and overt search, and then tested the theory in a covert search task with additive targets in simple noise backgrounds. We found that overall search performance was near optimal, given the detectability across the visual field (the d' map) of the human observers. However, surprisingly, detectability was substantially reduced in the foveal region, but not in the periphery. In other words, there is substantial “foveal neglect” that occurs when covert search is directed over an extended area. We propose to characterize and test principled hypotheses for this phenomenon and its role in covert search both in simple and natural backgrounds. In preliminary studies we also designed stimuli that isolate the role of the boundary cues available for identification of occluding targets. In these stimuli, the target and background have surface textures that are statistically the same. We will develop and test optimal and suboptimal models of identification of these maximally-camouflaged targets, both for noise and natural textures. Finally, we plan to measure and model overt search accuracy and eye movements for additive and maximally-camouflaged occluding targets.