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Visual Processing in Reading and Dyslexia

  • The present research combines different paradigm in the area of visual perception of letter and words. These experiments aimed to understand the deficit underlying the problem associated with the faulty visual processing of letters and words. The present work summarizes the findings from two different types of population: (1) Dyslexics (reading-disabled children) and (2) Illiterates (adults who cannot read). In order to compare the results, comparisons were made between literate and illiterate group; dyslexics and control group (normal reading children). Differences for Even related potentials (ERP’s) between dyslexics and control children were made using mental rotation task for letters. According to the ERP’s, the effect of the mental rotation task of letter perception resulted as a delayed positive component and the component becomes less positive when the task becomes more difficult (Rotation related Negativity – RRN). The component was absent for dyslexics and present for controls. Dyslexics also showed some late effects in comparison to control children and this could be interpreted as problems at the decision stage where they are confused as to the letter is normal or mirrored. Dyslexics also have problems in responding to the letters having visual or phonological similarities (e.g. b vs d, p vs q). Visually similar letters were used to compare dyslexics and controls on a symmetry generalization task in two different contrast conditions (low and high). Dyslexics showed a similar pattern of response, and were overall slower in responding to the task compared to controls. The results were interpreted within the framework of the Functional Coordination Deficit (Lachmann, 2002). Dyslexics also showed delayed response in responding to the word recognition task during motion. Using red background decreases the Magnocellular pathway (M-pathway) activity, making more difficult to identify letters and this effect was worse for dyslexics because their M-pathway is weaker. In dyslexics, the M-pathway is worse; using a red background decreases the M activity and increases the difficulty in identifying lexical task in motion. This effect generated worse response to red compared to the green background. The reaction times with red were longer than those with green background. Further, Illiterates showed an analytic approach to responding to letters as well as on shapes. The analytic approach does not result from an individual capability to read, but is a primary base of visual organization or perception.

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Author:Gunjan Khera
URN (permanent link):urn:nbn:de:hbz:386-kluedo-40077
Advisor:Thomas Lachmann
Document Type:Doctoral Thesis
Language of publication:English
Publication Date:2015/02/03
Year of Publication:2015
Publishing Institute:Technische Universität Kaiserslautern
Granting Institute:Technische Universität Kaiserslautern
Acceptance Date of the Thesis:2013/08/20
Date of the Publication (Server):2015/03/03
Number of page:116
I would like to acknowledge that Chapter 5 of my thesis was published in Frontiers in Evolutionary Neuroscience on 12th June, 2012 (Lachmann, Khera, Srinivasan, and van Leeuwen, 2012) and in the conference Proceedings for the International Society for Psychophysics (Lachmann, Khera, van Leeuwen, 2011). I have used slightly varied version in my thesis.
Faculties / Organisational entities:Fachbereich Sozialwissenschaften
DDC-Cassification:1 Philosophie und Psychologie / 150 Psychologie
Licence (German):Standard gemäß KLUEDO-Leitlinien vom 13.02.2015