Science fiction in the sense that what follows does start from known facts. Then there is what is intended to be plausible speculation from those facts.
My interest is in the subjective experience of colour, of black and white. Is there any sense in which these experiences can be said to vary, to vary from one person to another? Persons with more or less normal vision that is. This post tries to clear away some preliminaries.
As we move the pointer through the spectrum of visible light, what you get from a prism or a rainbow, say from left to right in the figure above, we experience the gamut of pure colours, that is to say colours produced by packets of light of a single wavelength, or at least confined to a fairly narrow band of wavelength. Black for absence is present, but white, a mixture, is absent. The magentas, mixtures of blue and red are also absent, round the back if we were to join the two ends of the band above together to make a colour circle.
Noting in passing that I find the rendering of violet rather unconvincing. Seems far too bright and light in hue to me. But that is another matter.
Visible light is mostly in the range 400 to 800nm (nanometres, a metric unit of length equal to one thousand-millionth of a metre) and, for example, yellow is around 590nm, roughly where the red receptor and the green receptor lines cross in the figure above – where the colour receptors in human eyes are called cones. The much more numerous rods do black and white.
High (right), medium and short (left), while I prefer to talk of red, green and blue, or RGB for short.
With the result that the red and green receptors are stimulated roughly equally, so the RGB signal reaching the brain from the eye is something like (100,100,0). However, as can be seen from the figure above, the same aggregate signal could be arrived at by mixing roughly equal amounts of light from a little to the right (red) and a little to the left (green). There is an infinite number of such mixtures which would deliver what is seen, what would be experienced, as the same shade of yellow.
The colour vision system is additive and works on the mixture of the signals delivered by the three sorts of receptor. So a bit of colour might really be yellow, sending out light at around 590nm, or the bit might actually be a judicious mixture of dots of red and green, aggregated by the vision system taken as a whole to yellow. The subjective result would be the same. A fact exploited by colour printing processes.
Let us work with the LWS-R hypothesis (for which see reference 1), according to which, inter alia, vision is delivered by the topically organised firing of neurons across a small patch of cortex. Where by topical we mean that the neurons are organised in a way that relates in a fairly simple way to what you might get in a two dimensional picture of the same scene. That is to say, if you could look at the neurons through a suitable microscope, you would recognise the scene.
Then colour is a property of that firing expressed over very small patches of cortex, over which there is a sustained and stable frequency mix of firing. The neurons in that very small patch are organised into three cohorts, each spread evenly across the patch and one cohort for each receptor. Within each cohort, the aggregate firing rate oscillates, at least approximately, with the frequency appropriate to that receptor.
The allocation of neuron to cohort varies according to circumstances. The LWS-R frame construction process draws on the base population of neurons according to the needs of the moment, according to the colour of the patch in question.
Some combination of time and space is needed to deliver the subjective experience: if there is more time you can get away with less space and vice-versa.
A natural assumption would be that the frequency of oscillation allocated to a receptor varies monotonically with the frequency to which the receptor is most responsive. So higher frequency oscillations of firing for blue receptors, lower frequency firing for red receptors and green in the middle. But, we argue that it might just as well be the other way around. Then, jumping from colour to black and white, the growing brain might do a similar trick with colour to that which Microsoft’s Powerpoint does with its invert black and white feature, with the figure above being an example of its use. No doubt Adobe’s Photoshop offers lots of tricks of this sort.
We have read recently of people who have four sort of colour receptor – cones – rather than the normal three. This could be accommodated in a straightforward way in the model above. Bearing in mind the need for room: from where I associate to the business of allocating radio frequencies bands to the various uses to which radio can be put.
Additional information
Note that there is no question of a population of neurons in a brain delivering oscillations at the frequency of those of visible light, say thousands of billions of hertz, even in aggregate, even though suitably organised aggregates can deliver much faster oscillations than the individuals can manage. The brain has to come up with some other solution.
I have read that if you give a person glasses which turn the world upside down, after a few days, the brain will turn it back up again. I wonder it something of the sort would happen if you had glasses which did the black and while inversion illustrated above?
In the foregoing, it is suggested that the subjective experience of colour is a straightforward matter of frequency, a fairly obvious candidate. But it might be something much more complicated. It might even be a matter of geometry, with the brain firing up lots of little hexagons or lots of little triangles. Perhaps plausible enough, but perhaps also requiring more neurons in the relevant part of the cortex than are actually available – which according to reference 3 might be around 5,000 to the cubic millimetre. But it does depend on where you look, with rather higher estimates being offered at reference 4 – and which also tells us that estimating this particular number is challenging.
Conclusions
We have offered a speculation about the delivery of the subjective experience of colour.
And to the extent that the frequencies chosen can vary, one might think that the subjective experiences might vary. Perhaps these frequencies are a function of some gene or other, a gene which comes in many varieties, like Heinz.
References
Reference 1: https://psmv4.blogspot.com/2020/09/an-updated-introduction-to-lws-r.html.
Reference 2: https://en.wikipedia.org/wiki/Visible_spectrum.
Reference 3: https://bionumbers.hms.harvard.edu/search.aspx.
Reference 4: https://www.pnas.org/content/pnas/105/38/14615.full.pdf. Gender differences in human cortical synaptic density - L. Alonso-Nanclares, J. Gonzalez-Soriano, J. R. Rodriguez, J. DeFelipe – 2008.
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