The relationship between high-level vision and reading ability

Abstract

Reading is a skill that is required for formal education, human communication, and cognitive development. Approximately 5-12% of the population display difficulties with reading because they are affected by developmental dyslexia (DD), a reading disorder that has a neurobiological origin. The most popular and well-developed theory of DD is the phonological deficit theory which postulates that problems with reading are as a result of failing to learn the relationship between spelling and sounds. However, the phonological account does not explain why many dyslexic readers have measurable visual deficits. Specifically, there is increasing evidence to suggest that impaired function in the magnocellular pathway, which is sensitive to low contrast, low spatial and high temporal frequency stimuli, is associated with reading difficulties. The purpose of the current set of experiments is to test if performance in high-level visual tasks, e.g., object recognition, is associated with reading ability, and to include conditions designed to bias the magnocellular pathway, as previous work has focused on lower-level tasks, e.g., contrast detection, and/or has not specifically included a magnocellular condition. In conditions where the magnocellular pathway was stimulated, slow readers typically performed significantly worse over a range of high-level visual tasks: object recognition, visual search, scene gist classification, emotional face perception and optical illusions. In contrast, differences were not observed between groups in chromatic conditions which suggests that the parvocellular pathway, associated with high spatial acuity and colour vision, is intact. It is suggested that the deficits seen here are as a result of dysfunctional magnocellular input to various high-level regions interfering with top-down facilitation, attentional mechanisms, and global processing. Intervention programmes for DD often focus on improving phonological processing. The data presented across this thesis highlights the potential of visual training programmes to specifically target and strengthen the magnocellular pathway to improve visual-based tasks. Specifically, the use of games and illusions provide an engaging, practical method for potentially identifying those at risk in the pre-reading phase. Targeting those at risk during this critical period can prevent a spiral of negative effects that can occur in individuals with dyslexia. Overall, the findings provide new insight into the link between reading ability and high-level visual processing.