The ability to inhibit responses is a central requirement for goal-directed behavior but has been dominated by a top-down or cognitive control view. Only recently, the role of bottom-up perceptual factors were focused in research. However, studies usually use clearly distinguishable stimulus categories to trigger response execution or inhibition. In the current study, we present a novel Gabor patch Go/No-go task to induce perceptual ambiguity during response inhibition. To examine the neurophysiological processes in detail, we use EEG recordings and combined temporal EEG signal decomposition methods with source localization analyses. We show that perceptual similarity between Go and No-go trials compromises response inhibition performance. Interestingly, the EEG data show that this is due to a modulation of stimulus-response transition or decision processes, and not purely stimulus-related processes. This was possible by applying a temporal EEG decomposition method. We provide evidence that a prefrontal P2 (pP2) likely reflects decision processes on action execution using stimulus information. These processes were associated with superior and middle prefrontal regions (BA8). When these processes fail, occasions to execute a response become misinterpreted as occasions to inhibit a response. Successful and unsuccessful decisions to inhibit a response under high perceptual ambiguity seem to further depend on how well "what-decisions," supported by neural mechanisms in BA19, can be processed. However, these what-decisions seem to be closely linked to the specification of the required action. Stimulus processing is closely linked to response programming so that response control is already informed when uncertainty with regard to stimulus identity is detected.NEW & NOTEWORTHY This study introduces a novel Go/No-go paradigm and shows what neurophysiological subprocesses and functional neuroanatomical are involved during inhibitory control when ambiguous stimulus input is provided. The results show that bottom-up perceptual processes are important to consider during top-down controlled response inhibition. Stimulus processing is closely linked to response programming so that response control is already informed when uncertainty with regard to stimulus identity is detected.
Keywords: EEG; perception; prefrontal cortex; response inhibition; source localization.