Abstract
Vision is a highly dynamic process. Saccadic eye movements are used to move retinal images of interest onto the fovea, while vergence eye movements act to minimise retinal disparity and maintain a single binocular view of the target which is brought into focus by ocular accommodation. Despite these ubiquitous disruptions to the retinal image we perceive a stable and clear visual world.Previous studies have revealed that this perceptual stability is partly due to suppression of low spatial frequency information in the visual scene during eye blinks, saccadic and vergence eye movements. The work in this thesis was aimed at exploring how dynamic ocular accommodation, that changes the ocular power to produce sharp retinal images of objects at different viewing distances, contributes to the perceptual stability of the external visual world.
The psychophysical and electro-physiological evidence presented here shows that visual suppression during dynamic accommodation does occur in addition to the reduction in sensitivity predicted by optical factors. This new type of reduced visual sensitivity was termed accommodative suppression. The accommodative suppression is selective for luminance modulated patterns of higher spatial frequencies around the time of peak velocity of fast dynamic accommodation responses and is independent of vergence eye movements, direction of accommodation, accommodative demand, changes in pupil size and attention.
The observed temporal characteristics of accommodative suppression suggest that the underlying neural mechanisms utilise proprioceptive feedback from within ciliary muscle, instead of corollary discharge signals elicited together with the motor command in midbrain areas as found for visual suppression triggered by extra-ocular muscle movements. A computational model was developed taking into account the relationship between the reduction in contrast sensitivity and accommodation velocity. The model may be implemented into algorithms of efficient artificial neural networks for visual information processing.
The new mechanism of visual suppression, operating during fast dynamic accommodation responses, may contribute to the perceptual clarity and stability of our visual environment.
| Date of Award | 2010 |
|---|---|
| Original language | English |
| Awarding Institution |
|
| Supervisor | Velitchko Manahilov (Supervisor), Niall Strang (Supervisor) & Dirk Seidel (Supervisor) |