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Vision

Vision
Aims
• To understand the anatomy and physiology of the visual system
• To understand the concept of neural adaptation

Introduction

We heavily rely on our eyes everyday for vision in order to perceive people, objects, and colours. Normal vision results when light rays from objects in the external environment are refracted by the cornea and the lens of the eye and focused onto the photoreceptors of the retina. Formation of an image on the retina is mainly concerned with focusing light rays involving four basic processes: refraction of light rays, accommodation of the lens, constriction of the pupil and, convergences of the eyes. This experiment looks at neural adaptation which is when neurons which are continuously being stimulated by a particular visual feature (colour, movement direction) become fatigued, the neurons that process the opposite colours or movement direction then start to respond at normal levels resulting in the vision of an afterimage (Engelmann 2004).

Results and Discussion

This experiment was divided into four parts; the first two on motion and the second two on colour. Both motion and colour were looked at via binocular and monocular aspects of vision.

Part 1A involved the prolonged view of a black and white rotating object for a certain period then an instant switch to a blank (white) screen. Upon view of the blank screen the object – an afterimage could be seen rotating in the opposite direction at a slower speed. At higher speeds, the afterimage appeared to rotate also at a faster rate in the opposite direction, and the afterimage seemed to get smaller with increased speed, that is only the rotating part of the afterimage began to concentrate towards the centre of the object as the speed of it increased.

The pathway involved with processing these motion signals begins with the photoreceptors – the rods and cones which transmit signals to the outer plexiform layer, where they synapse with the bipolar cells and...