Expectation in Sensory Processing and Perceptual Decision-Making

Abstract

At every level of sensory processing, prior experience contributes to the construction of the perceptual world. In the last two decades, there has been renewed interest in the mechanisms that implement these contributions and the implications for the broader understanding of the perceptual processing stream. This thesis sought to contribute to this growing literature, by examining the influence of prior experience in the early processing of sensory information, the evaluation of that sensory evidence in perceptual decision-making, and the outcome of these processes in perceptual experience. Chapter 2 suggests that perceptual awareness of stimuli in binocular rivalry is shaped by prior experience, but not in the fashion predicted by a prominent model of predictive perceptual processing. Chapter 3 provides evidence that violations of sensory expectations provoke responses at some stage of sensory processing, but the responses of an electrophysiological index of early sensory processing did not discriminate expected from unexpected stimuli. The primary advantage of accumulating evidence in perceptual decisions is the minimisation of noise, but few studies have investigated the decision process using stimuli with little physical noise. Chapter 5 demonstrates that perceptual decisions about low-noise stimuli also rely on the accumulation of evidence. Chapter 6 describes an investigation of the implementation of expectation in perceptual decision-making using neurophysiological indices of the key stages of the decision process. The study provides evidence that prior expectations lead to preparatory motor activity instantiating a starting point bias in the decision process, but there were also suggestions that the decision may have been shaped by a more complex interaction between several decision mechanisms. Together this research provides insight into the role of expectation in sensory processing and perceptual decision-making.