W4L1: Comparative Colour Vision

What is the basis of colour vision?

• Distinguishing b/w the cone photoreceptors, which are responsive to different parts of the visible spectrum

  • We want a colour vision system to provide the visual brain w/ information about the relative amount of energy in different parts of the visible spectrum

• Red vs Green

• Blue vs Yellow

What is light?

The portion of the electromagnetic spectrum where energy varies w/n frequencies that can influence the brain & the body

What is brightness discrimination & how does it work?

• Brightness discrimination: measuring the energy produced based on differences in what is being reflected

• Works by acquiring information about the total energy across the visible spectrum

What is colour?

The spectral composition of light reflected from an object

What are the 2 main roles of an opsin protein?

• Translate isomerisation of retinal into a biological signal

• Determine spectral sensitivity i.e. the wavelength of light that the retinaldehyde will absorb

What is the difference between colour perception & colour characteristics?

• Perception: generated in the brain

• Characteristics: determined by cone opsin amino acid sequences encoded in the genome

What is the most common form of colour blindness?

Deuteranopia? Inability to distinguish along R-G colour axis

Which human opsins are X-linked?

• Long wave-length sensitive i.e. red cone photoreceptors

• Medium wave-length sensitive i.e. green cone photoreceptors

What would adding a fourth cone type allow?

• Improved spectral resolution w/n the human visible range

• Extend light detection to UV part of visible spectrum

Which group of vertebrates is the only one to have re-evolved a third cone opsin gene?

Primates

What does red-green discrimination require?

The centre having an over-representation of one class vs the surround