Stopping Speed in the Stop-Change Task: Experimental Design Matters!

Previous research comparing the speed of inhibiting a motor response in no-foreknowledge vs. foreknowledge conditions revealed inconsistent findings. While some studies found stopping to be faster in the no-foreknowledge condition, others reported that it was faster in the foreknowledge condition. One possible explanation for the heterogeneous results might be differences in experimental design between those studies. Given this, we wanted to scrutinize whether it makes any difference if foreknowledge and no-foreknowledge are investigated in a context in which both conditions are presented separated from each other (block design) vs. in a context in which both conditions occur intermingled (event-related design). To address this question a modified stop-change task was used. In Experiment 1 no-foreknowledge and foreknowledge trials were imbedded in a block design, while Experiment 2 made use of an event-related design. We found that inhibition speed as measured with the stop signal reaction time (SSRT) was faster in the foreknowledge as compared to the no-foreknowledge condition of the event-related study, whereas no differences in SSRT between both conditions were revealed in the block design study. Analyses of reaction times to the go stimulus reflect that participants tended to slow down their go responses in both experimental contexts. However, in the foreknowledge condition of the event-related study, this strategic slowing was especially pronounced, a finding we refer to as strategic delay effect (SDE), and significantly correlated with SSRT. In sum our results suggest that inhibition speed is susceptible to strategic bias resulting from differences in experimental setup

The impact of experimental design on inhibitory control in an extended version of the stop-change task

Previous studies repeatedly compared inhibitory control processes in a condition with foreknowledge about the response that has to be inhibited versus a condition without such foreknowledge. Some of these studies found stopping to be slower and interference to be lower in the foreknowledge condition. Other studies, however, reported the opposite results. Differences in experimental design between those studies might be the reason for such inconsistent findings. The present dissertation therefore aimed to clarify whether inhibitory control processes in foreknowledge and no-foreknowledge condition differ between block and event-related design. In the block design study (Experiment 1) no-foreknowledge and foreknowledge trials were presented in separate blocks of trials; in the event-related study (Experiment 2) both trial types occurred intermingled. Both experiments made use of a modified Stop-Change Task, an extension of the classical Stop-Signal Paradigm. Results indicate that in the event-related study inhibition speed was faster in the foreknowledge condition, whereas in the block design study it did not differ between the two conditions (Gordi et al., 2019). Compared to the no-foreknowledge condition interference was reduced in the foreknowledge condition of both designs, although this effect between conditions was much greater in the event-related design. Participants slowed down their responses to the go stimulus in both experimental designs. However, greater go RTs in the foreknowledge vs. no-foreknowledge condition reflect that this delay was especially pronounced in the event-related study. The finding was referred to as strategic delay effect (SDE) as participants most probably implemented a strategy of waiting until they were sure that no signal to inhibit would be shown before they conducted the go response. The present dissertations’ results suggest that inhibitory control measures are “susceptible to strategic bias resulting from differences in experimental setup” (Gordi et al., 2019, p. 1) and underline the importance of a unified experimental approach when comparing inhibitory control processes in no-foreknowledge vs. foreknowledge condition

Strategies of selective changing: Preparatory neural processes seem to be responsible for differences in complex inhibition

Selective inhibition describes the stopping of an action while other actions are further executed. It can be differentiated between two strategies to stop selectively: the fast but global stop all, then discriminate strategy and the slower but more selective first discriminate, then stop strategy. It is assumed that the first discriminate, then stop strategy is especially used when information regarding which action might have to be stopped is already available beforehand. Moreover, it is supposed that both strategies differ in matters of basal ganglia pathways used for their execution. Aim of the present study was to investigate the use of the two strategies in situations requiring selective changing of an action. Eighteen healthy male participants performed a selective stop-change task with informative and uninformative cues during fMRI. Behavioral results show that informative cues led to a benefit in both inhibition times and selectivity. FMRI data revealed that the same cortico-subcortical pathway was used with informative and uninformative cues. Behavioral and neuronal results indicate that participants used the first discriminate, then stop strategy for selective inhibition irrespective of the amount of previously available information. Moreover, the neural activity data indicate that the benefit in the informed condition was produced by an efficient preparation for the concrete change process. Possible factors that might affect which strategy is used for selective stopping are the level of previously available information (foreknowledge) and the experimental set-up, as e.g. task complexity