How can no change in an auditory stimulus generate an N2b-P3a?

The purpose of this study was to investigate the occurrence of an endogenously-evoked no-go N2b. Previous literature focused on the N2b being evoked by exogenous auditory stimuli. In this study, no-go stimuli were the absence of a gap in a 1000-ms noise burst (i.e., no-gap trials). ERPs were measured from 35 participants while performing a gap-detection task and passively listening to the same stimuli. Participants were asked to press a button when they heard a gap in the noise burst (go trials) and to withhold their button press when they did not perceive a gap in the noise burst (no-go trials). The current study's gap-detection task had predictable timing (gaps always occurred at 500 ms after noise burst onset) and high probability of gaps occurring (10:1); therefore, participants built up an expectancy that gaps would occur on most trials at 500 ms. For no-gap trials, this meant that a participant's expectancy was violated and thus a N2b-P3a response was generated. We found that all participants had N2b-P3a responses to no-gap trials. Overall, this study demonstrated that the no-go N2b-P3a response can be evoked by an endogenous signal in the form of the omission of an expected gap in noise.