Unconscious perception can be predicted from prestimulus activity

A fundamental open question is vision science is why humans can make accurate guesses about stimuli they report not consciously seeing. We show that the objective accuracy of discriminating the location of a subjectively unconscious stimulus can be predicted in trial-by-trial manner from low frequency (1-15 Hz) electroencephalographic activity present before the stimulus. Accurate discrimination of unconscious stimulus location was supported by lateralized prestimulus neural activity that optimally suppressed non-relevant ipsilateral cortical signals or increased the excitability of contralateral visual cortex to weak stimuli. The effect was present up to 1 second before the stimulus was presented. Signal detection analyses indicated that this perceptual capacity lied on the same continuum as conscious vision. The results indicate that unconscious perception is not a distinct capacity, but relies on the same top-down mechanisms as conscious vision.