The proposed research concerns perception of, and memory for visual material (ranging from relatively simple stimuli such as digit arrays to more complex stimuli such as natural scenes). The research is framed largely within a theory, the sensory- response/information-acquisition rate theory that PI and his collaborators have been developing for the past three years. Of central importance to the research is methodology involving equivalence techniques. Equivalence techniques which - essentially entail determination of the rules by which different factors combine to produce equivalent internal states - allow conclusions which, unlike those allowed by evaluation of typical statistical interactions, can be generalized both to theoretical constructs (e.g., "strength") and to other dependent variables (e.g., d') that are nonlinearly related to the dependent variable that happens to be measured in a particular experiment (e.g., proportion correct). Five broad research topics are proposed, designed to investigate, (1) visual degradation (e.g., contrast) effects on visual perception and memory, (2) processing of and memory for visual stimuli decomposed into high and low spatial frequencies, (3) unification of two facets of everyday visual behavior-information acquisition and phenomenological appearance, (4) processing as a path through some multidimensional encoding space, (5) integration of information across a series of brief presentations that mimic eye fixations, and (6) the relation between confidence and accuracy in visual memory. Data and theory about normal visual processing provide a foundation for isolating causes of, and guiding solutions to abnormal or suboptimal visual processing. Suppose, for example, that an individual complains that he or she "just can't seem to keep up with what's happening in a complex visual environment." What is causing this problem? Is it, for example, simply a slowing of initial information acquisition? Is it a lack of ability to use appropriate contextual information to guide processing? Is it a lack of ability to manipulate acquired visual information in short- term memory? The proposed research will provide the empirical and theoretical technology that would enable a clinician to differentiate among these (and other) possible reasons for the difficulty.