Perceptual learning of the orientation structure of faces and textures

Abstract

Perceptual learning occurs because observers become more sensitive to informative aspects of the stimuli. Learning the informative aspects of one stimulus set does not transfer to another stimulus set of the same class. In this dissertation, the argument will be made that if observers learn how to discover informative aspects, learning will be more generalizable. However, discovery requires that the informative aspects are not easily apparent. To this end, stimulus orientation structure can be manipulated to contain informative structure in one orientation band, and non-informative structure in the other orientation band. Such a manipulation was inspired by research on face perception: Faces are best identified when decisions are based more on the horizontal relative to the vertical facial structure. Hence, the first three chapters focus on understanding the horizontal bias during face identification, and the final two chapters introduce a novel stimulus set for which horizontal bias may be learned. Chapter 2 identifies a neural marker of horizontal bias that is correlated with face identification accuracy, suggesting that we can predict how well observers identify faces based on their neural sensitivity to horizontal relative to vertical structure. Chapter 3 shows that when face identification accuracy declines due to healthy ageing, so too do behavioural and neural horizontal bias, but Chapter 4 shows that perceptual learning can increase horizontal bias in healthy older adults. Chapter 5 uses texture stimuli and shows that observers can learn to discover informative horizontal structure embedded in uninformative vertical structure. Chapter 6 extends these findings to show that adequate practice results in learning that generalizes to novel textures for which the orientation-selective processing is relevant. The results presented inform our understanding of the neural representations associated with orientation-selective processing, and suggest that observers can learn to discover informative structure conveyed by a particular orientation band.