Common neural mechanisms for response selection and perceptual processing

Behavioral evidence supports a dissociation between response selection (RS; stimulus-to-response [S-R] mapping) and perceptual discrimination (PD): The former may be subject to a central processing bottleneck, whereas the latter is not (Pashler, 1994). We previously (Jiang & Kanwisher, 2003) identified a set of frontal and parietal regions involved in RS as those that produce a stronger signal when subjects follow a difficult S-R mapping rule than an easy mapping rule. Here, we test whether any of these regions are selectively activated by RS and not perceptual processing, as predicted by the central bottleneck view. In Experiment 1, subjects indicated which of four parallel lines was unique in length; PD was indexed by a higher BOLD response when the discrimination was difficult versus easy. Stimuli and responses were closely matched across conditions. We found that all regions-of-interest (ROIs) engaged by RS were also engaged by perceptual processing, arguing against the existence of mechanisms exclusively involved in RS. In Experiments 2 and 3, we asked what processes might go on in these ROIs, such that they could be recruited by both RS and perceptual processing. Our data argue against an account of this common activation in terms of spatial processing or general task difficulty. Thus, PD may recruit the same central processes that are engaged by RS.