Giulia Gennari¹, Biyu J. He¹; ¹New York University Grossman School of Medicine

Our subjective reality corresponds to a continual stream of perceptual updates. Although our experience seems to unfold in real time, psychophysical evidence supports a two-stage model of perception: conscious updates are preceded by long-lasting periods of unconscious processing. This model posits a divergence in representational formats, with unconscious analysis preserving high spatiotemporal fidelity to the incoming input and conscious percepts reflecting simplified, post-hoc interpretations. Yet, the neural substrates of these two phases remain unknown. Here, we used magnetoencephalography and multivariate decoding to delineate the neural underpinnings of unconscious processing versus phenomenology. Subjects performed a motion-induced blindness (MIB) task, in which the illusory disappearances and reappearances of a salient target reflect perceptual updates that follow periods of unconscious processing. Decoders were trained on brief localizer trials where the target was physically present or physically absent. Because these trials involved no task, the decoders remained blind to MIB-related decisional or motor processes. Our analyses uncovered a dissociation between slow cortical potentials (SCP, 0.05-5Hz) and the amplitude of gamma-band activity (30-60Hz). Whereas classifiers trained on SCP successfully discerned target disappearances and reappearances in awareness, classifiers trained on gamma amplitude could do so only in phenomenally-matched control trials, where perceptual changes had a direct physical counterpart. During illusory blindness, gamma-band classifiers always predicted the target as “present”, indicating faithful tracking of the physical input. Leveraging systematic manipulations of the target’s visual attributes, we further examined sensory processing in relation to the currently perceived content. Neural patterns in the gamma band encoded target’s veridical features and their evolution with high precision, irrespective of conscious access. Conversely, SCPs supported the decoding of perceived features as they (re)entered awareness, irrespective of their sensory accuracy. Overall, these findings reveal a frequency-domain division of labor in the brain, with distinct activity orchestrating the temporal structure of perception.

Acknowledgements: This work was supported by the Leon Levy Foundation, by the Charles H. Revson Foundation and by the National Institute of Health (R01EY032085).