Information processing limitations during concept formation or learning processes are examined. Although individuals do acquire concepts quite well, these limitations cause them to use or exhibit their knowledge less effectively. Previous data suggest that individuals code a category in terms of its most frequent attribute values or that they abstract a central tendency of the exemplars of a class by which to represent a class. The goals are to test a response procedure which allows subjects to more readily demonstrate their knowledge and to explore the nature of processing limitations by examining the effects of speed stress on newly devised tasks. In four experiments, the complexity of the structure of the stimulus displays and the available processing time are manipulated and varied; the way in which subjects modify their processing as the tasks become more difficult is examined. In these experiments, the participants are exposed to a series of 100 concept acquisition trials. In the first experiment, test trial comparisons involve pairs of stimuli in which one stimulus dominates the other. In the second experiment, that dominance is removed, thereby, introducing greater complexity in the task. In the third and fourth experiment, time constraints on the subject's judgment during test trials are introduced.