Talking while looking: on the encapsulation of output system representations.

The idea that the human mind can be divided into distinct (but interacting) functional modules is an important presupposition in many theories of cognition. While previous research on modularity predominantly studied input domains (e.g., vision) or central processes, the present study focused on cognitive representations of output domains. Specifically, we asked to what extent output domain representations are encapsulated (i.e., immune to influence from other domains, representing a key feature of modularity) by studying determinants of interference between simultaneous action demands (oculomotor and vocal responses). To examine the degree of encapsulation, we compared single- vs. dual-response performance triggered by single stimuli. Experiment 1 addressed the role of stimulus modality under dimensionally overlapping response requirements (stimuli and responses were spatial and compatible throughout). In Experiment 2, we manipulated the presence of dimensional overlap across responses. Substantial performance costs associated with dual-response (vs. single-response) demands were observed across response modalities, conditions, and experiments. Dimensional overlap combined with shared spatial codes across responses enabled response-code priming (i.e., beneficial crosstalk between output domains). Overall, the results are at odds with the idea of strong encapsulation of output system representations and show how processing content determines the extent of interdependency between output domains in cognition.