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Identifier

000341167

Title

Επίδραση της ανομοιομορφίας του πλέγματος των φωτοϋποδοχέων στη διακριτική ικανότητα

Alternative Title

The effect of asymmetry in the photoreceptor mosaic on visual resolution

Author

Θεοδωράκης, Μ.

Thesis advisor

Παλλήκαρης, Ιωάννης

Abstract

It is known that the packing geometry and density of photoreceptors have an effect on the spatial resolution of the human visual system. The primary objective of this work is to evaluate the effects of deviations in the spatial symmetry of the photoreceptor mosaic on spatial resolution. To this end, the reported shape and spacing of cone photoreceptors are examined in the foveal, parafoveal and peripheral retina and compared against the normally perceived spatial resolution. Especially in the fovea, this is done assuming a symmetrical hexagonal photoreceptor mosaic and alternative models of retina tiling that result in quasi-symmetrical patterns of photoreceptors, without change in the mean cone density. It is verified that there is uniformly less aliasing reported for high spatial frequency stimuli, than would be expected if the sole limitation were the cone Nyquist frequency. In the fovea, when the optics as a limiting factor is bypassed, aliasing is produced only slightly above the Nyquist limit. Parafoveally, where the departure from symmetry is significant, the cone Nyquist limit is more easily overcome. In the periphery, aliasing never appears, but this is due to the scarcity of cones and great increase in receptive field size and neural undersampling. Therefore, it is assumed that the asymmetry in cone packing is a significant factor in detecting and understanding stimuli exceeding the Nyquist limit, along with ocular movements and higher processing in the visual cortex. Research that would help elucidate its exact effect should encompass alternative asymmetrical models of retina tiling, the effective application of blind deconvolution techniques in real time experiments and the evaluation of natural imagery, whose power spectrum seems to be more efficiently rendered on asymmetrical mosaics.

Language

Greek

Subject

Ophthalmology

Vision physiology

Issue date

2006-08-04

Collection

School/Department--School of Medicine--Department of Medicine--Post-graduate theses

Type of Work--Graduate theses

Notes

Διατμηματικό-μεταπτυχιακό πρόγραμμα σπουδών: "Οπτική και Όραση"