This research investigates the processing of visual and verbal information in tasks which require comparisons of visually presented stimuli. Particular concerns include what is stored when a subject has experience with a set of stimuli and how short-term codes for the stimuli are constructed and processed. These problems are investigated with two general paradigms. One is a same-different judgment task in which, for a series of trials, two consecutively presented pictures of common objects are judged to be the same or different according to some criterion. The criterion for sameness, interstimulus interval, and visual and semantic relationships between the stimuli are manipulated, and reaction time is the dependent variable. The second paradigm is a stimulus construction task. For a series of trials, the subject is first given a visual stimulus separated into basic components and then given a non-separated second stimulus. The subject's task is to mentally construct a non-separated representation of the first stimulus and indicate whether it matches the second. Manipulated variables include interstimulus interval, stimulus complexity, and number of components of the first stimulus. Reaction time is recorded. In both these paradigms, the reaction times are used as the basis for inferences about the nature, construction, and use of the memorial representations of the stimuli.