CHAPTER 1 | The human visual system

Category: Colour Theory and Perception | Type: Technical Fundamentals | Section: 1.2

1.2 The human visual system

• S-cones (blue-sensitive): Peak at approximately 420 nm

• M-cones (green-sensitive): Peak at approximately 535 nm

• L-cones (red-sensitive): Peak at approximately 565 nm

Fovea: A small area at the centre of the retina with a high concentration of cones and no rods. This is the area with the highest visual acuity and colour discrimination.

Optic nerve: Transmits the visual information from the retina to the brain.

1.2.2 From light to colour perception

The path from light to colour perception proceeds through several steps:

1. Phototransduction: When light reaches the retina, the photopigments in the cones absorb the light. This causes a biochemical reaction that ultimately results in an electrical signal.
2. Neural processing in the retina: The signals from the cones are processed by several layers of nerve cells in the retina, including bipolar cells and ganglion cells. This is where the first processing of colour information already begins, according to the opponent-process theory.
3. Transmission to the brain: The ganglion cells form the optic nerve, which sends the visual information to the brain.
4. Processing in the brain: The visual information is first processed in the lateral geniculate nucleus (LGN) of the thalamus and then forwarded to the primary visual cortex (V1) and higher visual areas in the occipital and temporal lobes.
5. Colour perception: Ultimately, these processes lead to our conscious experience of colour, influenced by both physiology and higher cognitive processes.