1 vergence movements: co-operative movements that keep both eyes fixed on the same target. 2 saccadic movements: rapid movement of the eyes make to maintain an image of a moving image upon the fovea. There are 3 types of cones in the human eye, each containing a different type of photopigment. Hue of a colour is determined by wavelength (ex: 540 nm = green) A colour"s brightness is determined by the intensity, or amount of energy, of the light that is being perceived. Third perceptual dimension of colour, saturation is roughly equivalent to purity (fully saturated colour consists of only one wavelength -> i. e. pure red) Vision = a synthetic sensory modality (synthesizes [puts together] rather than analyzes. Colour mixing: perception of two or more lights of different wavelengths seen together as light of an intermediate wavelength. Human visual system can synthesize any colour from various amounts of almost any set of.