The Psychophysical Characterisation of Dorsal and Ventral Stream Functions with Equivalent Noise Paradigm Normal Clinical Populations

  • Mahesh Raj Joshi

Student thesis: Doctoral ThesisDoctor of Philosophy (PhD)

Abstract

Global motion and global form are processed along the bifurcated visual processing pathways of dorsal and ventral stream. Global motion perception is reported to be affected more than the perception of global form in various developmental disorders, which has led to the suggestion of a dorsal stream vulnerability. However, a direct comparison of processing, deficits, or interaction between the two visual processing streams has remained difficult due to limitations in experimental design/stimulus.

In this current body of work, physically identical stimuli (random dot kinematograms for global motion and Glass patterns for global form) embedded in varying levels of noise were used to probe local/global processing in visually normal and clinical populations.

Our initial experiments revealed a higher sensitivity to global motion compared to global form perception in visually normal adults, which was due to an increased efficiency of the global integration mechanism in the motion domain. The results also showed that certain commonly used form stimuli may not target the global stage of form processing. The investigation of global motion and form interactions further revealed that such interactions may extend beyond local level processing at the primary visual cortex.

In order to evaluate complex visual processing effectively in the clinical arena, a more efficient paradigm is required. In the concluding chapters, a faster method was validated and employed to evaluate global motion and form perception in amblyopia a condition that has well documented global processing deficits.

Our results revealed motion and form processing deficits in strabismic amblyopia with relatively larger deficits found in the form processing mechanism -contradictory to the previously proposed dorsal stream deficiency in developmental disorders.

Overall our results showed that comparing motion and form processing is not a trivial task and careful consideration with regards to the experimental design/paradigms is required for an accurate comparison across the domains.
Date of Award2016
Original languageEnglish
Awarding Institution
  • Glasgow Caledonian University

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