Olicoeur, 2003). These get Aprotinin capacity sharing accounts postulate that parallel processing can occur, but Task 1 and Task 2 have to share limited processing capacity. When Task 1 is prioritized (explicitly or implicitly), most processing capacity will be allocated to this task; consequently, response selection in Task 1 processing will not be influenced much by the presentation of the second stimulus, whereas response selection in Task 2 can only start properly when the response to the first stimulus has been selected. But when the tasks are prioritized more equally, responding in both tasks will be influenced (e.g. Miller et al., 2009). Based on the PRP literature, we propose a capacity sharing account for performance in selective stop tasks. This is shown in Fig. 5. The top panel of this figure depicts go processing on no-signal trials; the middle panel depicts go and signal processing on signal trials in the consistent-mapping group; and the bottom panel depicts go and signal processing on signal trials in the varied-mapping group. We assume that the go and signal processes will interact for their whole duration when a signal is presented. Furthermore, we assume that processing the signals in the varied-mapping condition is harder than in the consistent-mapping condition (for the reasons discussed above). Consequently, the decision to stop or not will finish later in the varied-mapping condition than in the consistentmapping condition (indicated by the thick vertical lines in Fig. 5), and go and stop processing will interact for a longer period. This can easily explain the RT differences PD150606 structure between conditions. Fig. 5 shows that signal espond RT will be shorter than no-signal RT when the decision is easier (middle panel), whereas it will be longer than no-signal RT when the decision to stop or not is difficult (bottom panel). The figure also shows that the interaction between going and stopping will cause invalid-signal RT to be longer than nosignal RT, but this difference will be more pronounced in the varied-mapping condition than in the consistent-mapping condition. In other words, we do not have to assume that subjects in the varied-mapping condition used a categorically different strategy than subjects in the consistent-mapping condition. Our limited capacity sharing account can explain the RT patterns in both groups. Note that we have depicted stop-signal processing by a single bar, but we assume that many processes contribute to successfully stopping a response (see Section 3.5). Here we propose that response selection in the go task has to share capacity the decision to stop or not, which could involve retrieval or activation of the relevant signal rule, a comparison of the signal with the cue, conjunctive feature evaluation, or a combination of these processes. When the signal is considered to be valid, a neural inhibitory process will be activated. Interactive race models have shown that at this point, go and stop will also briefly interact. We have previously formalized the concept of `processing capacity’ as a measure of the rate of processing (Logan et al., 2014): A process has unlimited capacity if its rate is unchanged when another process enters the race, whereas it has limited capacity if its rate decreases asCognition. Author manuscript; available in PMC 2016 April 08.Author Manuscript Author Manuscript Author Manuscript Author ManuscriptVerbruggen and LoganPagemore runners enter the race (see also Bundesen, 1990; Logan Gord.Olicoeur, 2003). These capacity sharing accounts postulate that parallel processing can occur, but Task 1 and Task 2 have to share limited processing capacity. When Task 1 is prioritized (explicitly or implicitly), most processing capacity will be allocated to this task; consequently, response selection in Task 1 processing will not be influenced much by the presentation of the second stimulus, whereas response selection in Task 2 can only start properly when the response to the first stimulus has been selected. But when the tasks are prioritized more equally, responding in both tasks will be influenced (e.g. Miller et al., 2009). Based on the PRP literature, we propose a capacity sharing account for performance in selective stop tasks. This is shown in Fig. 5. The top panel of this figure depicts go processing on no-signal trials; the middle panel depicts go and signal processing on signal trials in the consistent-mapping group; and the bottom panel depicts go and signal processing on signal trials in the varied-mapping group. We assume that the go and signal processes will interact for their whole duration when a signal is presented. Furthermore, we assume that processing the signals in the varied-mapping condition is harder than in the consistent-mapping condition (for the reasons discussed above). Consequently, the decision to stop or not will finish later in the varied-mapping condition than in the consistentmapping condition (indicated by the thick vertical lines in Fig. 5), and go and stop processing will interact for a longer period. This can easily explain the RT differences between conditions. Fig. 5 shows that signal espond RT will be shorter than no-signal RT when the decision is easier (middle panel), whereas it will be longer than no-signal RT when the decision to stop or not is difficult (bottom panel). The figure also shows that the interaction between going and stopping will cause invalid-signal RT to be longer than nosignal RT, but this difference will be more pronounced in the varied-mapping condition than in the consistent-mapping condition. In other words, we do not have to assume that subjects in the varied-mapping condition used a categorically different strategy than subjects in the consistent-mapping condition. Our limited capacity sharing account can explain the RT patterns in both groups. Note that we have depicted stop-signal processing by a single bar, but we assume that many processes contribute to successfully stopping a response (see Section 3.5). Here we propose that response selection in the go task has to share capacity the decision to stop or not, which could involve retrieval or activation of the relevant signal rule, a comparison of the signal with the cue, conjunctive feature evaluation, or a combination of these processes. When the signal is considered to be valid, a neural inhibitory process will be activated. Interactive race models have shown that at this point, go and stop will also briefly interact. We have previously formalized the concept of `processing capacity’ as a measure of the rate of processing (Logan et al., 2014): A process has unlimited capacity if its rate is unchanged when another process enters the race, whereas it has limited capacity if its rate decreases asCognition. Author manuscript; available in PMC 2016 April 08.Author Manuscript Author Manuscript Author Manuscript Author ManuscriptVerbruggen and LoganPagemore runners enter the race (see also Bundesen, 1990; Logan Gord.
