PT - JOURNAL ARTICLE AU - Sasskia Brüers AU - Rufin VanRullen TI - At What Latency Does the Phase of Brain Oscillations Influence Perception? AID - 10.1523/ENEURO.0078-17.2017 DP - 2017 May 19 TA - eneuro PG - ENEURO.0078-17.2017 4099 - http://www.eneuro.org/content/early/2017/05/19/ENEURO.0078-17.2017.short 4100 - http://www.eneuro.org/content/early/2017/05/19/ENEURO.0078-17.2017.full AB - Recent evidence has shown a rhythmic modulation of perception: pre-stimulus ongoing EEG phase in the theta (4-8 Hz) and alpha (8-13 Hz) bands has been directly linked with fluctuations in target detection. In fact, the ongoing EEG phase directly reflects cortical excitability: it acts as a gating mechanism for information flow at the neuronal level. Consequently, the key phase modulating perception should be the one present in the brain when the stimulus is actually being processed. Most previous studies, however, reported phase modulation peaking 100 ms or more before target onset. To explain this discrepancy, we first use simulations showing that contamination of spontaneous oscillatory signals by target-evoked ERP and signal filtering (e.g. wavelet) can result in an apparent shift of the peak phase modulation towards earlier latencies, potentially reaching the pre-stimulus period. We then present a paradigm based on linear systems analysis which can uncover the true latency at which ongoing EEG phase influences perception. After measuring the impulse response function, we use it to reconstruct (rather than record) the brain activity of human observers during white-noise sequences. We can then present targets in those sequences, and reliably estimate EEG phase around these targets without any influence of the target-evoked response. We find that in these reconstructed signals, the important phase for perception is that of fronto-occipital ∼6Hz background oscillations at about 75 milliseconds after target onset. These results confirm the causal influence of phase on perception at the time the stimulus is effectively processed in the brain.Significance Statement When investigating the relationship between ongoing EEG oscillations and perception in humans, most studies report a peak influence of the EEG phase before stimulus onset. Yet, we should also be able to measure these effects post-stimulus, when the target is actually processed by the brain. First, we use simulations to show that a combined influence of the target-evoked potential and filtering can explain the lack of post-stimulus phase modulation in typical studies. Crucially, we then introduce a paradigm to uncover the true latency at which phase influences perception. The “white-noise paradigm” allows us to model background oscillations without target-evoked potentials. For the first time, we show that a theta-band ongoing oscillation influences perception ∼ 75 ms after target onset.