Paper presented at the Association for Research in Otolaryngology MidWinter Meeting (2015, February), Baltimore, Maryland, USA

Title: Integrated Sensory Predictions of Both What and When in Beta Band Oscillation: Unexpected Pitch in Rhythmic Entrainment

Authors: Andrew Chang, Dan Bosnyak & Laurel J. Trainor

Affiliation: Department of Psychology, Neuroscience & Behaviour, McMaster University

Key words: EEG, sensory prediction, rhythmic entrainment

Abstract: The neural basis of predicting what (predictive coding) will occur next and when (predictive timing) it will occur have typically been investigated separately. Beta band (15-25 Hz) oscillations in auditory cortex reflect predictive timing in that fluctuations in the power of beta band activity (BBA) predict the expected onset timing of the next beat during rhythmic entrainment. However, BBA also reflects predictive coding in that the power and phase of BBA increases following a mismatch between a perceived event and its expected content. Therefore, we hypothesized that BBA might reflect an integrated sensory prediction system crossing both what and when domains. In a series of experiments, we recorded EEG while subjects passively listened to an auditory oddball sequence with a fixed inter-onset interval (IOI) of 500 ms, in which 80% or 90% of the tones were a standard pitch (262 Hz) and 20% or 10% were a deviant pitch (494 Hz). We performed wavelet time-frequency decomposition to the source waveforms from right primary auditory cortex. In Experiment 1, the deviant tones were randomly dispersed in the sequence (and therefore not predictable). In addition to replicating the BBA power fluctuation predicting onset timing, the unexpected deviant tones induced a low-beta band (15-20 Hz) power increase after the deviant tones that was not present after the standards. This BBA increase was larger when the occurrence rate of deviant tone was lower (10% vs. 20%). In Experiment 2, we compared a predictable version (every fifth tone was a deviant) to an unpredictable version. We found that the power increase in BBA after the deviant tones was larger when the deviant tones were unpredictable than predictable. In contrast, the phase consistency of BBA was increased more following deviant than standard tones, but it was not modulated by predictability of the deviants. In Experiment 3, we presented the sequence of Experiment 1 at two additional tempos (390 and 610 ms IOI). The preliminary results of experiment 3 replicate previous work showing that the prediction of when the next tone is expected follows the tempo (IOI). However, a BBA increase following deviant tones remained for all tempos. Our results to date suggest that BBA power reflects top-down sensory prediction of upcoming auditory events, while BBA phase reflects bottom-up responses to rare events. In general, we have shown that beta band oscillation activity in auditory cortex is co-modulated by sensory prediction of both what and when.