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Browsing by Subject "dyslexia"

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    Visual Constraints on Reading in Normal Vision, Low Vision and Dyslexia
    (2020-12) Atilgan, Nilsu
    Reading is one of the most important daily visual tasks. Majority of people become expert readers at a very young age and perform this complex task effortlessly and automatically throughout most of their lives. However, in this “effortless” task, multiple complex processes must be efficiently carried out in a very short amount of time. That is why, reading processes and their underlying mechanisms have been a great interest for researchers. For decades, researchers have been studying the constraints that prevent people from becoming “experts” in reading. These constraints may result from many different sources such as sensory limitations, cognitive disabilities, linguistic difficulties and so on. This thesis focuses on some of the sensory constraints that affect reading performance and present three studies that approach these constraints from different angles. Chapter 1 gives an overview of the thesis. Chapter 2 addresses the close relationship between text properties and reading performance. Specifically, in this chapter, the joint impact of print-size and display-size limitations on reading speed is investigated. The findings indicate that a minimum number of characters per line, which is determined by print-size and display-size constraints together, is required to achieve a criterion of 80% of maximum reading speed. Chapter 3 discusses the neural substrates of crowding, the inability to recognize objects when surrounded by other objects, which is directly related to reading performance given the nature of text materials (i.e. letters are surrounded by other letters). Specifically, the relationship between object recognition performance in crowding settings and the nature of visual parallel pathways (i.e. Magnocellular and Parvocellular pathways) were examined. The results showed that the magnitude of crowding is different depending on the visual stimuli and their relative engagement in the visual parallel pathways. For example, processing of spatial forms like letters is affected by crowding the most while color processing does not seem to be impaired by the crowding effect. Finally, Chapter 4 investigates the visual limitations in reading through testing people with dyslexia. Visual span, the number of identifiable letters at one fixation, and visual crowding were studied to examine the differences between typical readers and individuals with dyslexia. In addition, various standardized assessments and Flashcard reading speed tests were administered to examine the individual differences, and potentially the sub-groups of dyslexia. Chapter 4 aims to address the relationship between individual differences and the performance in visual-attentional tasks in dyslexia. The findings indicated that despite large individual variabilities in the assessments and visual experiments, the dyslexia group on average demonstrated slower reading speeds, narrower visual span profiles and larger critical spacing values compared to the control group. Together, these three studies provide a better understanding of sensory factors that limit reading performance.