Response inhibition has been widely explored using the stop signal paradigm in the laboratory setting. However, the mechanism that demarcates attentional capture from the motor inhibition process is still unclear. Error monitoring is also involved in the stop signal task. Error responses that do not complete, i.e., partial errors, may require different error monitoring mechanisms relative to an overt error. Thus, in this study, we included a “continue go” (Cont_Go) condition to the stop signal task to investigate the inhibitory control process. To establish the finer difference in error processing (partial vs. full unsuccessful stop (USST)), a grip-force device was used in tandem with electroencephalographic (EEG), and the time-frequency characteristics were computed with Hilbert–Huang transform (HHT). Relative to Cont_Go, HHT results reveal (1) an increased beta and low gamma power for successful stop trials, indicating an electrophysiological index of inhibitory control, (2) an enhanced theta and alpha power for full USST trials that may mirror error processing. Additionally, the higher theta and alpha power observed in partial over full USST trials around 100 ms before the response onset, indicating the early detection of error and the corresponding correction process. Together, this study extends our understanding of the finer motor inhibition control and its dynamic electrophysiological mechanisms.

Electrophysiological working memory (WM) research has shown that distinct brain areas communicate through macroscopic oscillatory activities across multiple frequency bands. Such cross-frequency interactions generate nonlinear amplitude modulations (AM) in the observed signal. Traditionally, the AM of a signal is expressed as coupling strength between the signal and a pre-specified modulator at a lower frequency. Therefore, the idea of AM and coupling cannot be separately studied. This EEG study shows that the AM of parieto-occipital alpha/beta power and the coupling between frontal theta phase and parieto-occipital alpha/beta AM provide different information on WM processing. Thirty-three participants completed a color recall task with simultaneous EEG recording. The results showed that individual differences in WM precision are associated with frontal theta power enhancement and parieto-occipital alpha/beta power suppression. Furthermore, the AM of parieto-occipital alpha/beta power predicted WM precision after presenting a target-defining probe array. The phase-amplitude coupling (PAC) between frontal theta phase and parieto-occipital alpha/beta AM increased with WM load during the processing of incoming stimuli, but they did not predict the subsequent recall performance. These results indicate that the frontoparietal PAC reflects the executive control for selecting relevant WM representations, but whether the memorized information can be retrieved depends on the subsequent amplitude variation of parieto-occipital alpha/beta power. In conclusion, individuals with higher working memory precision are associated with enhanced frontal theta power and parieto-occipital alpha/beta power suppression.