Chapter 6

Chapter summary

Light is a form of energy that can be described as a ray, a wave, and a stream of particles known as photons or quanta. All three aspects of light are important for vision. Three important measures of light as a stimulus for vision are its intensity (number of quanta), contrast between the lightest and the darkest parts of an image, and wavelength (which is the basis for colour vision).

Humans have single-chambered eyes in which transparent cornea and lens form an image on the inner surface of the eye (retina). Photoreceptor cells called rods and cones transmit neural signals through the network of neurons in the retina to the optic nerve and on to the brain. The structure of the eye represents a compromise between properties which maximise spatial resolution and those which maximize sensitivity to light.

Eye movements are mediated by six extra-ocular muscles. Eye movements serve to shift our gaze to objects of interest, to stabilize our gaze when objects move, and to achieve binocular fixation on objects at different distances.