Unravelling the dynamics of response force: Investigating motor restraint and motor cancellation through go/no-go and stop-signal tasks

Prior research has found that the go/no-go (GNG) task primarily reflects participants' motor-restraint process, while the stop-signal task (SST) primarily represents participants' motor-cancellation process. However, traditional binary keyboards used in these experiments are unable to capture the subtleties of sub-threshold response-force dynamics. This has led to the neglect of potential sub-threshold motor-inhibition processes. In two experiments, we explored sub-threshold inhibition by using a custom force-sensitive keyboard to record response force in both GNG and SST. In experiment 1, participants displayed increased response force when correctly rejecting no-go targets in the GNG task compared to the baseline. In addition, they exhibited higher response force in hit trials than in false alarms, revealing engagement of both motor-restraint and motor-cancellation processes in GNG. Initially, participants utilised motor restraint, but if it failed to prevent inappropriate responses, they employed motor cancellation to stop responses before reaching the keypress threshold. In experiment 2, we used participants' average response-force amplitude and response-force latency in SST stop trials to characterise the motor-cancellation process. Average amplitude significantly predicted false-alarm rates in the GNG task, but the relationship between response latency and false-alarm rates was insignificant. We hypothesised that response latency reflects reactive inhibition control in motor cancellation, whereas average amplitude indicates proactive inhibition control. Our findings underscore the complexity of motor inhibition.