A brief justification is needed here for the use of SS>GS as our earlier studies have contrasted SS and SE trials. There are a couple of issues to consider in the use of SS>SE vs. SS>GS to identify the correlates of response inhibition. Whereas SS does not involve an overt motor response, both SE and GS do. Compared to SS, SE is highly salient and engages a wide array of cortical and subcortical structures, including the thalamus, insula, and midbrain (Li et al., 2008). In contrast, SS is more salient than GS. Thus, the question about which contrast to use in the regression against SSRT to identify the correlates of response inhibition hinges on conceptualizing the relationship of saliency response and inhibitory control. Since our earlier publications, our thinking has evolved that a critical component of motor inhibition as required of the SST is triggered by saliency processing of the stop signal (Cai et al., 2014; Cai et al., 2015; Hampshire and Sharp, 2015) and a proper contrast would have to index this saliency response. Thus, a contrast of SS>GS
