The Effect of positional noise and colours on reading performance in human vision

Abstract

Enhancing visual function is an important aspect of vision care. Reading difficulties among adults and children may adversely affect their quality of life through work and school education (Stifter et al., 2005). Changes in lighting and colour are known to influence visual comfort and reduce perceptual difficulties that affect reading for those with poor vision (Northway et al., 2010). In the initial experimental chapters of this thesis a visual noise model is used to simulate different levels of reading performance in young participants to investigate how reading performance, including reading rate and correct reading rate, is affected by changing the lighting conditions of the reading task. The first experiment chapter (Chapter 3) investigates the effect of introducing visual noise to a reading task in young participants with good near vision. Reading performance reduced when visual noise was introduced for both reading types (lexical and sub-lexical). The reading rate for sub-lexical words was slower than the reading rate for lexical words as the introduced noise disrupted word recognition or created cortical noise. The second experiment chapter (Chapter 4) investigates the effect of changing wavelengths or colours on reading performance when visual noise is introduced in participants with good vision. We found that the reading rate is not affected by changing wavelength or colour for both reading types. In the lexical words condition, however, introducing cortical noise affected word recognition differently with different wavelengths. The role of short wavelength and white colour in enhancing orthographic reading and word recognition is clear as it reduces the effects of positional noise (reducing the effects of cortical noise). The correct reading rate change differently with different wavelengths, even when positional noise is introduced. In sub-lexical words, the reading rate was almost same under different wavelengths and colour. However, the reading rate under long wavelength (red) was slower compared with other wavelengths and colour in both reading types. The third experiment chapter (Chapter 5) investigates the effect of changing the wavelength and colour on reading performance for amblyopic participants monocularly (amblyopic and non-amblyopic eyes) with and without cortical noise for both reading types. We found that the reading rate in amblyopic eye under different wavelengths and colour with and without cortical noise in different reading types was slower than the reading rate in non-amblyopic eyes. In non-amblyopic eyes, the reading rate reduction with lexical words was varied as varied the wavelengths and colour when cortical noise created. However, with sub-lexical words the reduction in reading rate was almost same under different wavelengths and colour. In amblyopic eyes, the reading rate reduction with with both reading types was almost similar but the reading rate in sub-lexical words was slower than lexical words. Also, the reading rate under long wavelength was the lowest compared other colours in all conditions. The fourth experiment (Chapter 6) investigates the effect of changing colours on central crowding reading for normal participants and how the object can be affected by changing the flanker distance and unflanked target. We found that central reading crowding is considered as a type of visual crowding. Also, different colours have different effects on central crowding. However, central crowding reading with red was not affected by changing the flankers.