colour 2 Flashcards
what is the physiology and neuroanatomy underlying colour processing of cone signals
chromatically opponent retinal ganglion cells
chromatic tuning in LGN, V1 and V2
V4 (and cerebral acrhomatopsia)
what psychophysical evidence is there for opponency
coloured after effects arise from adaption at multiple stages
habituation experiments
how can colour processing explain colour appearance
explaining the unique hues
flexible relationship between lights (the physical stimuli) and appearance (our perception)
how is colour information extracted from cone readout
comparison between cone classes
the relative variation in light’s spectral energy as a function of e(𝜆) read from ratio of cone excitations
preserved even when light intensity changes
when the spectrum is altered the ratios change
as long as these are not metamers, the colour will change
how is chromatic opponency implemented in ganglion cells
gaglion cells make the comparison of ratios explicit
midget ganglion cells are L-M opponent and have on-off receptive fields that are spatially and chromatically opponent (although unclear whether the surround is M cone signal specific or randomly wired with L and M cones)
small bistratified ganglion cells are S-opponent
compared with LM signals combined
only chromatically opponent
how are ganglion cell RFs organised
ganglion cells feed three separate pathways of the LGN, they differ in size RF and cone contact
what are the properties of parasol ganglion
10% of all retinal ganglion cells, large spatially opponent, chromatically non-opponent RF, projects to magnocellular layers in LGN, L and M cones input via diffuse bipolar cells (probably not S cones), poor chromatic selectivity
what are the properties of midget ganglion cells
60-80% of all retinal ganglion cells
RFs are 2-3x smaller and spatially and chromatically opponent
project to the parvocellular layers of the LGN
L or M input to centre, antagonistic surround from complementary type or L&M mixture (probably not S cones)
good chromatic selectivity: cherry-teal
what are the properties of small bistratified ganglion cells
4% of all retinal ganglion cells
larg spatially non-opponent, chromatically opponent RF
project to the koniocellular layers of the LGN
S input, opposed by spatially overlapping L plus M inputs
good chromatic selectivity lilac-lime
what are the different retinogeniculate pathways
magnocellular
parvocellular
koniocellular
what are the properties of the magnocellular pathway
not colour selective
poor spatial resolution
fast
(movement)
what are the properties of the parvocellular pathway
colour selective
good spatial resolution
slow
(objects)
what are the properties of the koniocellular pathway
colour selective
very poor spatial resolution
very slow
how is colour represented in cone-opponent DKL space
L+M+S signal: white-black (intensity)
S-(L+M) signal: lilac-chartreuse (small bistratified ganglion)
L-M signal: cherry-teal (midget ganglion)
Hue corresponds to Azimuth (angle around the plane)
Saturation corresponds to elevation in the plane
how are cells in the visual pathway chromatically tuned
plotting populations of chromatically opponent cells on the axis elevation and azimuth reveals that they cluster around 0-90* (Derrington et al., 1984)
90 azimuth K-cells, S-opponent small bistratified
90 elevation M-cells, parasol
0 azimuth P-cells L/M opponent midget
repeating these measurements in different areas of the visual system shows that in V1 chromatic tuning is more evenly distributed around the hue circle