Human vision and function/Part 1: How the eye works/1.3 Light stimulus and the eye/Answers

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1. What happens when a photoreceptor absorbs a photon of light? A nerve impulse is triggered and the impulses are sent to the brain.

2. Apart from rods and cones, what other cells are found in the retina? Ganglion, Bipolar, Amacrine, Horizontal.

3. Which photoreceptor is most sensitive to light? Rod. They only need one photon of light to trigger a response and don’t differentiate different colours.

4. What three wavelengths of light are the cone photoreceptors sensitive to? Blue, green and red.

5. In what section of the retina are the cones mostly found and what is the impact of this distribution? Cones are most concentrated at the centre of the retina (at the macula). The further from the macula you go, there are less cone photoreceptors. The impact of this is that vision is most sensitive in the centre of the vision and less sensitive in the periphery.

6. What is the blind spot? This is the section of the eye where the optic nerve exits the eye at the retina. There are no photoreceptors here and this is why it’s called a blind spot.

7. What happens to the fibres of the optic nerve at the chiasm? Half the fibres (the nasal fibres of each optic nerve) cross over at the chiasm to the other side.

8. Vision is decoded in the occipital cortex. Where are movement and sensation decoded? Movement is decoded in the frontal lobe and sensation is decoded in the parietal lobe.

9. How is the receptive field of the retina organised? It has a centre and a surround. I can be “on centre off surround” field, or the opposite, “off centre on surround”.

10. Where in the brain does decoding of lines and edges occur? At the occipital lobe.