The Karlin and Kestenbaum experiment is typical of PRP experiments, making use of simple tasks such as choice reaction time (but see Carrier & Pashler, 1995, for an exception). Such cognitively lean experiments do not map closely onto what has been the main goal of ACT-R, which is the modeling of higher-level human cognition. In order to make PRP experiments more cognitive, we have selected two relatively simple tasks that also include an important cognitive component: memory retrieval. ACT-R has a strong theory of memory retrieval based on the activations of declarative units and spreading activation from the goal. Thus, including a retrieval component augments the simple perceptual-motor requirements of the typical PRP task to provide a true perception-cognition-action experiment. One of the most well-developed theories of retrieval with ACT-R is in the domain of arithmetic (Chapter 9, this volume); so, we chose single-digit multiplication and addition as the two tasks for our experiment. This allowed us to manipulate the difficulty of Task 2 by varying the size of the operands involved in the problem.