Seeing things

I sometimes suspect that I return to the same topics time and again. Not too often I hope, because that will put people off reading this blog (in case anyone does!) This is possibly a topic which I may have already addressed, but hopefully this post will be interesting anyway.

It seems obvious to me that we all see things differently, and I’m talking about vision here, not “seeing” as a philosophical point of view. Some are short sighted, some long sighted, and others have impaired vision. I see a colour as a shade of blue, while my wife sees it as a shade of green.

One could argue that the difference is merely where the line is drawn, but I think that it is more than that. Apart from the physical differences in the lenses of our our eyes, we may have differences in the physical structure of the rest of our eyes, perhaps in the rods and the cones, and it is highly likely that the physical structures of our brains are different, and our minds (which I think of as the software that runs of the hardware of the brain) are definitely different.

It’s no surprise then that my wife and I disagree on whether a colour is a shade of blue or of green. (Actually we disagree about a lot of things. I believe that it goes with being married for 40+ years!)

In Googling around as I write this post I found an article about the brain’s colour processor. Interestingly it has a section entitled “Color is Personal” which is a part of my theme for this post. This section, however, is not really relevant to my theme as the author then discusses Achromatopsia, where damage to the colour processor causes all sensation of colour to disappear.

It seems that even in our own brains and thinking processes the idea of colour is not fixed. I read another article which describes our own personal perception of colours as “malleable”. The implication of this is that a person might describe a colour as “a shade of green” one day, and “a shade of blue” on another day. Is there no hope of a definitive answer?

A physicist could help us out, couldn’t he/she? He/she could measure the frequency of the light and say, definitively, that the colour is blue, or it is green, couldn’t he/she? Well, sort of. This would work for very simple colours, but real world colours are rarely made up of just one colour. The scientist’s scope would likely show a range of frequencies resembling a mountain range. That blue/green colour might have traces or red or violet, and is fairly certain to have more than one peak in the blue/green range.

Albert Einstein showed us that if a scientist was moving at a high speed relative to us, he/she would measure the frequencies in the colour differently from a scientist whose spectroscope was alongside us and not moving or moving at the same speed as us.

The ambient light has an effect on the colours that we perceive. A red object in red light doesn’t look red. Other objects of different colours look different in a red light. Similarly, it is difficult to determine the colours of cars and other objects under the yellow/orange sodium lights. According to Wikipedia, the colour of a street light has effects other than simple colour perception – it appears to affect peripheral vision.  New LED technology may be able to remove some of these deficiencies.

There are innumerable effects which affect or perception of colour. The most recently famous illusion is the dress which appears to people to be either black and blue or white and gold, but there are many such illusions. One which I came across a long time ago is the chessboard illusion. In this illusion, two square appear to be different colours, but are in fact the same colour. This illusion is usually shown in monochrome, but the illusion works in colour too, and depends on the shadow of the cylinder to produce the effect.

One brain is very like any other brain. When a scientist shows someone a colour on a card, the same areas of the brain show activity in all individuals, if we exclude some cases where brain function is abnormal for some reason. We can’t delve very much deeper into this issue as we don’t know what this activity signifies, beyond the bare fact that the person was shown a card with a colour on it. We certainly can’t tell if they see it as a shade of blue or a shade of green, and we can’t tell what their subjective experience is when the brain activity occurs.

In some individuals a number or letter may invoke a sensation of colour. Such people might have the sensation of seeing something green when they think of or read the number 6. I don’t know if this imprinted behaviour because the person was presented with a green symbol when first learning their numbers or whether or not it was merely a chance association that arose at a different time, or indeed if it was because of some neurological happening or trauma that has allowed the association to happen.

Anyhow, when we see something, there are many stages to the process that  starts with light leaving the object, reaching our eyes, being refracted by the lens of the eye to form an image on the retina at the back of the eye, being sensed by the rods and cone cells in the retina, and sending signals to the brain, which then processes the data.

The amazing thing here is that the image sent to the brain is pretty messy. The eye is not a perfect sphere, the retina is curved in three dimensions and the resolution is pretty rubbish. The retina has at least one major gap in it, rods and cones are not evenly distributed across the retina. Our perception however, is smooth and break free. We have our image processing hardware and software in the brain to that for that.

It means we can watch a soccer match, and we can see the black and white panels or the ball rotating as it spins across the television screen, when the unprocessed image that reaches our eyes may be quite blurred. Seeing is believing!