Psychological Review 1990, Vol. 97, No. 2. 253-270 Copyright 1990 by Ihe American Psychological Association, Inc. 0033-295X/90/$00.75 Dimensional Overlap: Cognitive Basis for Stimulus-Response Compatibility— A Model and Taxonomy Sylvan Kornblum University of Michigan Thierry Hasbroucq Cognitive Neurosciences Unit Centre National de la Recherche Srientifique Marseille, France Allen Osman University of California, San Diego The classic problem of stimulus-response (S-R) compatibility (SRC) is addressed. A cognitive model is proposed that views the stimulus and response sets in S-R ensembles as categories with dimensions that may or may not overlap. If they do overlap, the task may be compatible or incompati- ble, depending on the assigned S-R mapping. If they do not overlap, the task is noncompatible regardless of the assigned mapping. The overlapping dimensions may be relevant or not. The model provides a systematic account of SRC effects, a taxonomy of simple performance tasks that were hitherto thought to be unrelated, and suggestive parallels between these tasks and the experimental paradigms that have traditionally been used to study attentional, controlled, and automatic pro- cesses. In this article, we address the classic problem of stimulus- response (S-R) compatibility (SRC). A model is proposed that attempts to provide a systematic account of performance in highly compatible, incompatible, and noncompatible tasks. At the core of our model is the idea that when a particular S-R ensemble produces either high or low compatibility effects, it is because the stimulus and response sets in the ensemble have properties in common, and elements in the stimulus set auto- matically activate corresponding elements in the response set. Noncompatible tasks are those in which the stimulus and re- sponse sets have nothing in common. If the activated response is the required one, it will be executed rapidly and correctly; if it is not, then it will be relatively slow and error prone. Whether a particular S-R ensemble will produce compatibility effects is often quite easy to determine because of the relationship be- tween the stimulus and response sets. In the part of the model that treats the representational aspects of the problem, we pos- tulate that this relationship is based on the commonality, simi- This research was supported in part by National Institute of Mental Health Grants MH43287 and MH37145, Office of Naval Research Grant N00014-89-J-1557, and North Atlantic Treaty Organization Grant RG 86-0215 to Sylvan Kornblum and by a grant from the Fyssen Foundation to Thierry Hasbroucq. We thank Harold Hawkins, Steve Keele, David Meyer, Lindsay Oliver, Jean Requin, David Rosenbaum, J. E. K. Smith, Tony Whipple, and an anonymous reviewer for helpful comments. Correspondence concerning this article should be addressed to Sylvan Kornblum, Mental Health Research Institute, University of Michigan, 205 Washtenaw Place, Ann Arbor, Michigan 48109-0720. Electronic mail may be sent to: Sylvan_Kornblum@um.cc.umich.edu or GBDV @umichum.bitnet. larity, or correspondence of the sets in the ensemble. We call this the dimensional overlap of the ensemble. The automatic response activation mechanisms, as well as the response identi- fication processes underlying SRC effects, are the processing as- pect of the model. Even though the model is still in its qualita- tive development phase, it is able to make ordinal predictions concerning several different SRC effects, such as the effects of mapping, irrelevant dimensions, and number of alternatives. These effects had been viewed as unrelated empirical phenom- ena, and most of the work on SRC has dealt with them as mani- festations of unique, nongeneralizable properties of particular dimensions or specific tasks. This approach has led to different accounts being proposed for "spatial," "symbolic," "sensori- motor," and "semantic" tasks. Our model attempts to break with such past approaches in a fundamental way by proposing to account for most major SRC effects in terms of common basic cognitive mechanisms. This unitary approach leads to a taxonomy of SRC tasks that reveals striking similarities be- tween them and suggestive parallels with the experimental para- digms that have traditionally been used to investigate atten- tional, controlled, and automatic processes. Background on SRC SRC: The Term Stimulus-response compatibility refers to the fact that some tasks are easier or more difficult than others either because of the particular sets of stimuli and responses that are used or be- cause of the way in which individual stimuli and responses are paired with each other. For example, if a set of digits are used as stimuli, a particular digit generally can be paired more easily with its own name as the response than with the name of a city 253