Post-Stop-Signal Adjustments: Inhibition Improves Subsequent Inhibition Patrick G. Bissett and Gordon D. Logan Vanderbilt University Performance in the stop-signal paradigm involves a balance between going and stopping, and one way that this balance is struck is through shifting priority away from the go task, slowing responses after a stop signal, and improving the probability of inhibition. In 6 experiments, the authors tested whether there is a corresponding shift in priority toward the stop task, speeding reaction time to the stop signal. Consistent with this hypothesis, stop-signal reaction time (SSRT) decreased on the trial immediately following a stop signal in each experiment. Experiments 2– 4 used 2 very different stop signals within a modality, and stopping improved when the stop stimulus repeated and alternated. Experiments 5 and 6 presented stop signals in different modalities and showed that SSRT improved only when the stop stimulus repeated within a modality. These results demonstrate within-modality post-stop-signal speeding of response inhibition. Keywords: cognitive control, inhibition, post-stop-signal slowing, sequential control adjustments, stop- signal paradigm Cognitive control is required to balance the demands of the ever-changing environment. One common task used to investigate cognitive control is the stop-signal paradigm (Lappin & Eriksen, 1966; Logan & Cowan, 1984), which directly pits a go task against a stop task. Performance in the go task requires speed, and per- formance in the stop task requires caution. Control adjustments are necessary to achieve a balance between going and stopping, and one common adjustment is the slowing of go reaction time (RT) after a stop signal occurs (Bissett & Logan, 2011a; Emeric et al., 2007; Rieger & Gauggel, 1999; Verbruggen, Logan, Liefooghe, & Vandierendonck, 2008). One explanation for post-stop-signal slowing is that it is a goal-priority shift away from the go task (Bissett & Logan, 2011a). Slowing of go RT will improve sub- jects’ ability to stop, increasing their probability of inhibition. But this does not mean that the stop process itself is affected. In six experiments, we examine whether the priority shift away from the go task after stop trials is coupled with a priority shift toward the stop task, measured in faster stop-signal reaction time (SSRT). Several studies suggest that successive stop trials may slow SSRT. Van den Wildenberg, van der Molen, and Logan (2002) had subjects prepare for a no-go response and found an increase in SSRT during the preparatory period. Bissett, Nee, and Jonides (2009) also found an increase in SSRT following a visual stimulus that predicted a no-go trial. Verbruggen and colleagues found slower SSRT on trials that required inhibiting incompatible re- sponses in Stroop and flanker (Verbruggen, Liefooghe, & Vand- ierendonck, 2004) and Simon tasks (Verbruggen, Liefooghe, Note- baert, & Vandierendonck, 2005). However, Morein-Zamir, Chua, Franks, Nagelkerke, and Kingstone (2007) found faster SSRT in a task that required subjects to stop applying a constant pressure if they had also stopped applying pressure on the previous trial. The critical difference between the studies showing slower and faster SSRTs may lie in the similarity of the stop tasks and stop signals. Studies that found slower SSRT compared different tasks and different stop stimuli, whereas the study that found faster SSRT compared the same task with the same stop signal. This motivates the evaluation of stimulus differences and modality differences in the present study. Morein-Zamir et al. (2007) used an unusual stop task, which motivates the investigation of more typical stop tasks in the present study. Stop-Signal Paradigm In the stop-signal paradigm, subjects typically perform a choice RT task (the “go” task) and are asked to withhold their response when a stop signal occurs on a random subset of trials. The delay between the go stimulus presentation and the stop signal (stop- signal delay, or SSD) is adjusted to manipulate the probability of inhibition. When SSD is short, subjects frequently inhibit their responses, but as SSD increases, the probability of inhibition decreases. These findings have been explained with the “horse race” model (Logan & Cowan, 1984), which assumes that a go process, initiated by go stimulus onset, races against a stop pro- cess, initiated by stop-signal onset. If the go process finishes before the stop process, subjects fail to inhibit, producing a signal- respond trial. If the stop process finishes before the go process, subjects succeed at inhibiting, producing a signal-inhibit trial. Stop-signal delay biases the race between stop and go processes: Short SSDs bias the race in favor of stopping and thereby increase the probability of inhibiting; long SSDs bias the race in favor of going and thereby increase the probability of responding. SSD is often adjusted with a staircase procedure, increasing after signal- inhibit trials and decreasing after signal-respond trials to yield a This article was published Online First January 23, 2012. Patrick G. Bissett and Gordon D. Logan, Department of Psychology, Vanderbilt University. This research was supported by Grant BCS-0957074 from the National Science Foundation. Correspondence concerning this article should be addressed to Patrick G. Bissett or to Gordon D. Logan, both at Department of Psychology, Vanderbilt University, Nashville, TN 37240. E-mail: patrick.g.bissett@vanderbilt.edu or gordon.logan@vanderbilt.edu Journal of Experimental Psychology: © 2012 American Psychological Association Learning, Memory, and Cognition 2012, Vol. 38, No. 4, 955–966 0278-7393/12/$12.00 DOI: 10.1037/a0026778 955