Two types of response inhibition failures in humans

Response inhibition is a key control function that allows humans to perform safe, goal-directed behaviors. The dominant behavioral-computational model holds that response inhibition fails when the inhibition process is too slow to intercept unwanted movements. However, many have hypothesized that some inhibitory failures instead result from a failure to launch the inhibition process altogether. Since no method exists to identify individual 'trigger failure' (TF) trials, they are hitherto a largely hypothetical phenomenon. We combined Bayesian process-mixture modeling with likelihood ratio testing and jackknife resampling to identify TF trials in 253 humans. We find that TF indeed represent a separate category from other inhibitory failures. Unlike other inhibitory failures, TF do not result from premature responses. Furthermore, TF lack a stop-signal P3 event-related potential, a neural index of response inhibition. Surprisingly, TF do not result from perceptual/attentional lapses. Thus, TF are a qualitatively distinct class of executive failure during response inhibition.