Spatial contrast sensitivity and external noise: applications to optical and neural modulation transfer functions

Abstract

The thesis will show how to equalise the effect of quantal noise across spatial
frequencies by keeping the retinal flux (If-2) constant. In addition, quantal noise
is used to study the effect of grating area and spatial frequency on contrast
sensitivity resulting in the extension of the new contrast detection model
describing the human contrast detection system as a simple image processor.
According to the model the human contrast detection system comprises low-pass
filtering due to ocular optics, addition of light dependent noise at the event of quantal absorption, high-pass filtering due to the neural visual pathways, addition of internal neural noise, after which detection takes place by a local matched filter, whose sampling efficiency decreases as grating area is increased.
Furthermore, this work will demonstrate how to extract both the optical and
neural modulation transfer functions of the human eye. The neural transfer
function is found to be proportional to spatial frequency up to the local cut-off
frequency at eccentricities of 0 - 37 deg across the visual field. The optical
transfer function of the human eye is proposed to be more affected by the
Stiles-Crawford -effect than generally assumed in the literature. Similarly, this
work questions the prevailing ideas about the factors limiting peripheral vision by showing that peripheral optical acts as a low-pass filter in normal viewing
conditions, and therefore the effect of peripheral optics is worse than generally
assumed.

Date of Award	Aug 1995
Original language	English
Supervisor	Jyrki Rovamo (Supervisor)