Cones, Blobs and Colours: Neuroscience in an artistic way
This is probably the first The-Half-Decent-Pharmaceutical-Chemistry-Blog-ish post. In fact, I put a nice artwork in order to smart up the whole thing.
You can say it's a double inspiration: Andy Warhol's Mao's portrait has been a frequent memory while studying how human brain analyzes colours.
So, this is my tribute to Andy Warhol: it's called Four Colours.
Atoms and molecules absorb light with a certain wavelength and the colour we perceive is its complementary. The object reflects or emits light with the remaining wavelengths.
Everybody knows we have two kinds of photoreceptors, namely cone and rod cells: cones are less common among the animals and fewer than rods in human retina.
Cones are concentrated in the part of the retina called fovea, which is the one we see with in daylight: we use to move it to focus our attention.
There are three different types of cones (Trichromatic Theory), generally referred as Blue, Green and Red. However, considering the sensitivity of their pigments, it is definitely more correct to name them S-, M- and L-cells (small, medium and long wavelength). Or, if you like colours, Blue, Bluish-Green and Yellowish-Green.
According to the wavelength of the light emitted by the object, the three cones are differently stimulated and their responses, in terms of frequency of action potential, vary.
Cone cells are connected to parvocellular ganglion cells only. The information, then, goes through magnocellular layers of the lateral geniculate nucleus and, reaches the primary visual cortex (V1).
Blobs are a group of cells of V1, located in the third layer. Blobs process colour information as cone cells, with the cells activated by specific wavelengths.
The information is sent to V2 rough stripes and, finally,the analysis of colour finishes in V4, where there are neurons which are sensitive to a small range of wavelength: this guarantees a very accurate analysis.
V4 cells are responsible for colour constancy too: looking at a complex scene (i.e. with varying lightning conditions), the colours of objects do not change.
In the end, the processed data are transmitted to the association temporal cortex.
