Being able to predict when an event will occur (temporal predictability) can help us prepare and time our responses. We here sought to delineate the neural and behavioural corollaries of highly implicit, probabilistic temporal predictability in an auditory foreperiod paradigm. To this end, we measured electroencephalography (EEG) and response times in two independent experiments (total N =46). Unbeknownst to participants, we induced a probabilistic variation of cue-target delays (i.e., foreperiods) in a pitch-discrimination task on a noise-embedded tone: The smaller the standard deviation of the underlying foreperiod distribution, the more predictable the time of target occurrence should be. Both experiments showed that more predictive foreperiods sped up listeners' responses. Crucially, neural signatures of temporal predictability emerged when comparing EEG activity between conditions of varying temporal predictability. First, cue-related P2 evoked responses were less pronounced for cues that implicitly signalled temporal predictability of target occurrence. Second, in both experiments, fronto-central delta (1-4Hz) phase coherence was found relatively reduced during predictive foreperiods. Concomitantly, in Experiment II, the most predictive condition yielded a central alpha (7-12Hz) power increase just before the most likely time point of tone onset, likely reflecting improved temporal orienting of attention. In sum, neural oscillations in anticipation of, and response times to a target show that humans are susceptible to even strictly implicit, probabilistic temporal regularities.
Keywords: Alpha; Delta; EEG; Implicit timing; Temporal hazard; Temporal predictability.
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