in contrast to traditional models of cognition, which often posit the one-way flow of sensory information from the periphery towards more remote areas of the brain, clark has suggested a two-way "cascade of cortical processing" underlying perception, action, and learning. the concept of predictive processing lies at the heart of this view, wherein top-down predictions attempt to correctly guess or "explain away" bottom-up sensory information in an iterative, hierarchical manner. discrepancies between the expected signal and actual signal, in essence the "prediction error," travel upward to help refine the accuracy of future predictions. interactions between forward flow of error (conveyed by "error units") and backward flow of prediction are dynamic, with attention playing a key role in weighting the relative influence of either at each level of the cascade (dopamine is mentioned as "one possible mechanism for encoding precision" with regard to error units). action (or action-oriented predictive processing) also plays an important role in clark's account as another means by which the brain can reduce prediction error by directly influencing the environment. to this, he adds that "personal, affective, and hedonic" factors would be implicated along with the minimization of prediction error, creating a more nuanced model for the relationship between action and perception.