Introduces a technique to study the flow of information through processing stages in choice RT tasks. The technique was designed to determine whether response preparation can begin before stimulus identification is complete ("continuous" models), or if a stimulus must be fully identified prior to any response activation ("discrete" models). To control the information available at various times during stimulus identification, some relevant stimulus characteristics were made easy or difficult to discriminate. Ss were 68 right-handed undergraduates. The usefulness of partial output was varied by manipulating the assignments of stimuli to responses. For some mappings, partial information could contribute to effective response preparation because the responses consistent with partial information were assigned to fingers on the same hand; for other mappings, partial information was assigned to fingers of different hands. Performance differences between these mappings were considered evidence that partial information about a stimulus was transmitted to response activation processes before the stimulus was identified and thus were considered evidence against discrete transmission of information about the stimulus as a whole. Results suggest that information is transmitted discretely with respect to stimulus codes, although distinct codes activated by a single stimulus may be transmitted at different times.