The Effect of Positional Noise in Age Related Reading Strategies

  • Abhishek Mandal

Student thesis: Doctoral ThesisDoctor of Philosophy (PhD)


Our visual world contains a vast number of objects at various locations in a three dimensional space. How we process these objects in the brain depends upon many factors including retinal function, the visual pathway and the oculomotor responses. When performing real life tasks such as reading, combined eye movements during changes in fixation will potentially result in the retinal images being distorted, but the words are usually perceived as stable and clear. The degraded information is removed from awareness by saccadic, vergence and accommodative suppressions.

The first experimental chapters in this thesis examine the visual suppression mechanism when we change fixation. During the experiment, participants’ visual performance was measured during changes in fixation from distance to near at different angles within the visual scene. Visual suppression to low spatial frequency gratings was found around the onset of the saccadic/vergence eye movements reflecting both saccadic suppression and vergence suppression. The results also suggested that suppression of high spatial frequency information occurs that is similar to predicted accommodation suppression values. These results suggest that suppression of visual information during combined eye movements helps to maintaining stability in the visual environment and is likely to be used to maintain high quality vision during reading.

The second set of experimental chapters investigated age-related changes in reading performance by measuring reading speed with a newly developed reading chart which embeds noise within the words. In all participants the results showed that reading duration increased linearly as a function of positional noise variance within the words. However in vi real word conditions the older adults were affected to a greater extent by the introduction of noise. These findings suggested that healthy older adults experience noise-exclusion deficits associated with binding letters into holistic word percepts when reading real words while the ability to process phonological information is preserved in normal aging. Impaired ability to bind local elements and construct global percepts may lead to weakened use of memory which in turn may diminish the memory function to learn from experience and to retain knowledge.

In subsequent chapters the reading chart was modified for clinical use and reading speed parameters were collected in dyslexic groups. In a dyslexic participant, reading speed and eye movement patterns were studied when reading text embedded with positional noise. Poor fixation control was noticed in the dyslexic participant, suggesting that oculomotor abnormalities may contribute to reduced reading speed in dyslexies. These studies suggest that the newly developed noise induced reading charts may provide useful information about reading performance in a number of clinical groups.
Date of Award2019
Original languageEnglish
Awarding Institution
  • Glasgow Caledonian University
SupervisorNiall Strang (Supervisor), Dirk Seidel (Supervisor) & Gunter Loffler (Supervisor)

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