Great Expectations: The Neural Mechanisms of Prediction and Attention in Visual Awareness

Abstract

Mechanisms of attention and prediction operate in the service of visual perception and subjective awareness. Attention enhances the processing of sensory stimuli that are relevant for guiding behaviour (Posner, 1994), whereas prediction uses prior information to guide the processing of new sensory input. Despite their convergent functions, attention and prediction have traditionally been cast as independent mechanisms and exhibit seemingly antagonistic effects on neural activity: attention enhances, whereas prediction suppresses, neural responses to sensory stimuli (Schröger, Marzecová, & SanMiguel, 2015). Recently, however, predictive coding theory has reconciled these effects under a new theoretical framework that casts attention and prediction as synergistic determinants of perceptual awareness (Feldman & Friston, 2010). Perceptual experience is proposed to reflect an inference about the causes of sensory inputs, whereas attention is the inference about the uncertainty of those causes. Mechanistically, attention is proposed to optimise precision expectations by increasing the gain of units encoding the difference between predicted and observed sensory events (so-called 'prediction errors'). Predictive coding theory generates several important hypotheses about the interdependent relationships between attention, prediction, and awareness, which are explored in this thesis. First, attention is proposed to be an inference about the uncertainty of environmental states, rather than the states themselves, and therefore should be dissociable from awareness. Although recent research supports this hypothesis for certain types of attention, it remains unclear whether spatial attention can dissociate from awareness at the level of neural representations. Second, prediction is proposed to facilitate awareness by building a generative model of likely sensory events. Consistent with this theory, recent research has demonstrated that sensory templates are activated immediately prior to stimulus onset (Kok, Mostert, & de Lange, 2017), but it remains unclear how these templates influence visual awareness. Third,