Improving Letter Recognition and Reading in Peripheral Vision: Sensory and Cognitive Constraints

Abstract

Reading is an important daily task, but it is very difficult for people who have lost their central vision, because they must use peripheral vision to read. One hypothesis for slow reading speed in peripheral vision is the shrinkage of the visual span, which is the number of identifiable letters within a glimpse. Previous studies have shown that perceptual training tasks of letter recognition can enlarge peripheral visual span, as well as improving peripheral reading speed by 40% or more. This thesis focuses on sensory and cognitive factors that facilitate or limit the training-related improvements, with an ultimate goal of developing rehabilitation protocols for people with central-field loss. Chapter 1 gives an overview of the thesis. Chapter 2 demonstrates that there are common constraints limiting the size of the visual span across languages (Korean and English), and that extensive training of reading Korean characters using peripheral vision enlarges Korean visual span as well as English visual span. This transfer of training suggests a pre-symbolic nature of the visual span, and a strong potential for training benefits to generalize to untrained scripts. Chapter 3 discusses visual crowding, the inability to recognize objects in clutter, which is proposed to be the major sensory factor limiting the size of the visual span and reading. The results lead to the conclusion that reducing the impact of crowding can enlarge the visual span and can potentially facilitate reading, but not when adverse attentional bias is introduced, for example directing attention to one specific, small area in the visual field. By dissociating the influence of sensory and attentional factors, the link between crowding, visual span and reading was clarified. Finally, Chapter 4 reports on a study where the training was implemented in a word-guessing video game. The game training successfully enlarged the visual span and improved reading speed. Embedding the training in a game enhanced the enjoyment of the training and can temporarily boost letter-recognition performance during the game, but the quality of the training was not altered compared with similar training without the game. Together, the studies presented in this thesis not only speak to the theoretical basis for the training-related changes, but also provide practical guidance for designing potential reading rehabilitation protocols for people with central-field-loss.