Consciousness = learning? The role of recurrent processing in perceptual learning

The starting point of this thesis is a neural definition of consciousness, independent of attention or other cognitive functions that are required for a behavioral report. It is defined as recurrent processing (RP) - which is needed for integration of information - as opposed to unconscious feedforward processing. As RP is mediated by NMDA receptors, it is hypothesized that consciousness (according to the neural definition) plays a role in learning. Using EEG, I showed that stimuli that evoked RP yet were unattended (and therefore unreportable) are learned at the perceptual level, whereas attended yet masked stimuli (for which RP was blocked) do not show any learning effects. Interestingly, the behavioral learning effect only became apparent when performance feedback was given. This suggests that the memory trace formed during inattention was latent until reactivated by behavioral feedback. A follow-up fMRI experiment revealed that performance feedback boosts neural learning effects as well. In addition, when NMDA receptors are manipulated with ketamine (thereby reducing RP), visual feature integration is diminished and perceptual learning precluded. Together, these results provide a first step in understanding the benefit of defining the distinction between unconscious and conscious processing as the divide between feedforward and recurrent processing respectively. It allows us to understand consciousness on a more fundamental level, by understanding its function: consciousness is needed for learning. It would be interesting to investigate how far the current findings extend beyond the perceptual learning domain, and to further elucidate the role of feedback in reconsolidating latent memory traces.