Representation of the prediction of silence at sensory and higher cognitive levels of cortical processing

The unpredicted omission of expected sound, that is “silence”, elicits omission N1, N2 and P3 (early and late oN1, oN2, oP3) event-related potential (ERP) and pupil dilation responses (PDR), which are interpreted as prediction error signals located along different processing levels. This study aims to investigate whether these responses to unpredicted silence can also be elicited by the unpredicted continuation of sound, that is, the “absence” of expected silence. A prediction error response to the absence of silence would indicate that silence was predicted including the levels of processing on which a prediction of silence was established. Participants (27 women, 10 men) pressed a button every 1-2s while exposed to continuous Brownian noise. Button presses predictably (88% of trials), randomly (50% of trials) or never (0% of trials; motor-control) interrupted the noise. EEG and pupil diameter data were recorded. We found that the unpredicted absence of a silent interval in the noise elicited late oN1 (~150ms) and oN2, oP3 and PDR omission prediction error responses. However, we did not find an early oN1 (~100ms). Predictive representations of silence can be established at the level of categorical sensory processing (late oN1) and at the levels of later, higher cognitive processing and attention (oN2, oP3, and PDR), but not at the level of feature-based, early cortical sensory processing (early oN1), possibly because the absence of features cannot easily be encoded. These results suggest that silence is represented not only as the absence of sound but also as a predictable event in itself.