Table 2.

Experimental medicine tasks that provide measures of response inhibition in humans

Task	Task description	Key performance outcomes	Potential implementation and analytics issues
Go/No-Go task / Affective Go/No-Go task *	In the classic Go/No-Go task the participant must respond rapidly to a cue (e.g., X) but withhold a response when a no-go stimuli is shown (e.g., O). Typically target stimuli are presented more frequently than non-target stimuli (e.g., at a ratio of 3:1) in order to elicit prepotent responses to the target stimuli. Go/No-Go tasks that include affective or disease-relevant stimuli have been developed (Hege et al., 2015; Lyu et al., 2017; Mobbs et al., 2011). False alarms are the key performance outcome associated with response inhibition. Other measures include errors of omission, hits, successfully inhibited responses, and reaction times for hits. Some researchers calculate target sensitivity and/or response bias, although these appear to be less favored in the literature (Meule, 2017), possibly because interpretation is more unclear. Where different conditions have been employed, endpoints are explored by task condition, e.g. false alarms to affective stimuli vs. false alarms to neutral stimuli. Task is often quite long (approximately 15 minutes) to allow for a sufficient number of false alarms (Hege et al., 2015; Lyu et al., 2017). If adopting an affective version of the Go/No-Go, affective stimuli can be paired with the Go or the No-Go response, or both, and the task can take a block design or a mixed trials design. Block designs can allow investigation of the participants' ability to shift between rules (Meule, 2017). However, this can extend task duration and increase participant burden. Stop Signal Reaction Time task / Affective Stop Signal Reaction Time Task* Participants	False alarms are the key performance outcome associated with response inhibition. Other measures include errors of omission, hits, successfully inhibited responses, and reaction times for hits. Some researchers calculate target sensitivity and/or response bias, although these appear to be less favored in the literature (Meule, 2017), possibly because interpretation is more unclear. Where different conditions have been employed, endpoints are explored by task condition, e.g. false alarms to affective stimuli vs. false alarms to neutral stimuli.	Task is often quite long (approximately 15 minutes) to allow for a sufficient number of false alarms (Hege et al., 2015; Lyu et al., 2017). If adopting an affective version of the Go/No-Go, affective stimuli can be paired with the Go or the No-Go response, or both, and the task can take a block design or a mixed trials design. Block designs can allow investigation of the participants’ ability to shift between rules (Meule, 2017). However, this can extend task duration and increase participant burden.
Stop Signal Reaction Time task / Affective Stop Signal Reaction Time Task *	Participants perform a continuous or repetitive motor response, for example repeatedly pressing a button or touching a screen, in response to a ‘go’ cue. On some trials the ‘go’ cue is proceeded by a ‘stop’ cue indicating that the participant should withhold the response. The task can be modified to include affective stimuli, for example by presenting affective images prior to the go cue (Kalanthroff et al., 2013) or using affective stimuli as the go or stop cues (Svaldi et al., 2014).	Stop signal reaction time (SSRT), which is a measure of the speed of inhibiting the response after the stop cue has been given. Since correct inhibitions result in a lack of response the SSRT cannot be directly measured, and therefore mathematical models such as the independent race model (Logan and Cowan, 1984) are used to estimate the SSRT based on other endpoints such as the RT on unsuccessful stop trials, RTs on go trials, and the probability of making a false response.	There can be challenges when estimating the SSRT. Researchers must ensure that task design is appropriate for the given population, generating sufficient number of both successful and unsuccessful stop trials. Analysts must ensure that the underlying assumptions of the mathematical model are met before estimating the SSRT, otherwise estimates and therefore conclusions may be unreliable. See Verbruggen et al. for a comprehensive review of challenges in the design and analysis of the Stop Signal Task (Verbruggen et al., 2019). Task duration is approximately 10 minutes.
Stroop / Emotional Stroop *	Participants must respond to one feature of presented word stimuli, which is incongruent, on some trials, with the semantic properties of the word presented. For example the word ‘blue’ is presented in red color font, and the participant must name the color and inhibit the prepotent response to read the word. In the affective version of the Stroop, and those based on substances of abuse, disease-relevant word stimuli may produce attentional biases towards or away from the stimuli, compared to neutral word stimuli.	Accuracy and reaction time (for correct responses) for each trial type (e.g., incongruent vs congruent stimuli, or diseaserelevant vs. neutral).	As with the Affective Go/No-Go task, the Emotional Stroop can be implemented in either a block design or a mixed design. Stroop tasks are usually implemented with either button-press responses or vocal responses. However, we are not aware of comparative research which compares and contrasts these response types. Finally, there is a choice of whether or not to use masked stimuli. Duration of task incorporating several stimulus categories is roughly 5–10 minutes.

^*If using image stimuli, there are considerations to be made about sourcing and selecting images (see main text).