PSYCH 2220 Perception Lecture 8 Seeing in colour

PSYCH 2220 Perception Lecture 8 Seeing in colour

Isaac Newton Spectrum Colour mixing (additive, subtractive) Metamers Trichromacy (Young and Helmholtz)

Figure 9. 7 Color mixing with paint. Mixing blue paint and yellow paint creates a paint that appears green. This is subtractive color mixture.

Figure 9. 9 Absorption spectra of the three cone pigments. From Dartnall, H. J. A. , Bowmaker, J. K. and Mollon, J. D. (1983). Human visual pigments: Microspectrophotometric results from the eyes of seven persons. Proceedings of the Royal Society of London B, 220, 115 -130.

Short wavelength cones rods Medium and long wavelength cones

COLOUR VISION DEFICIENCIES Monochromat Dichromat (all mammals except primates) Trichromat (primates)

ISHIHARA PLATES

x x

Trichromacy vs opponency Can explain colour matching Young & Helmholtz Can explain adaptation Hering

OPPONENCY THEORY - - - ? -

Colour opponency is found at the level of RETINAL GANGLION CELLS

On centre off centre magnocellular parvocellular

CONCLUSION Both trichromacy and colour opponency are correct

P-pathway essential (parvocellular) Lesions in inferotemporal can cause achromatopsia Colour blobs

Motion vs still Colour vs grey

SIMULTANEOUS COLOUR CONTRAST

COLOUR CONSTANCY DIFFERENT SOURCES OF ILLUMINATION HAVE DIFFERENT SPECTRAL CONTENT. But colours look (relatively) the same.

http: //www. youtube. com/watch? v=TVUr. Hf 2 kc. UM