By Monish Chhabra ǀ January 15, 2019

The colours that we see, are all due to one particular type of cell in our eyes called - ‘cone’.

These cones are also responsible for any activity that requires fine visual detail – reading, driving etc.

All these cones – 6 million of them - are densely packed in a tiny pit on the retina of our eyes. This small depression - 1.5 mm in diameter - is called ‘fovea’.

Anything that requires accurate vision, is done at this site. Fovea is only 1% of the size of the retina, and contributes more than 50% of the optical signals that our brain receives.

Humans have three types of cones. Each of these respond to a different wavelength of light, thus perceiving three basic colours – blue, green and red.

However, since we receive signals from all three cone types simultaneously and each cone can pick up 100 different gradations of colour, our brain can perceive a continuous range of colours. This gives an average human the ability to discern more than a million different colours.

Fishes and birds have an extra type of cone cell, thus possessing four colour receptors. This allows them to detect additional wavelengths, which often includes ultraviolet.

On the other hand, most carnivore animals have only two types of cones, thus reducing their visual perception to only two basic colours.

Having fewer colour receptors gives them a different advantage. They have a higher ability to distinguish between colours in dim light. This gives them an edge when hunting in the dark.

In humans, when one of the three cone pigments are missing or not functioning properly, it leads to colour blindness. The most common such blindness is between red and green items. In such cases, an average human can still distinguish about 10,000 different colours.

Women are less likely to have colour blindness, as compared to men. This is because, two cone cell genes are present on the X chromosome. Since women have two sets of X chromosomes, in case one is defective, the other set can compensate for it.

This also makes women more likely to have multiple cone cell pigments, thus increasing their ability to distinguish between more colours. More than half of the women can discern colours better than men.

What we look at, and what we see

The fovea sees only the central two degrees of the visual field; approximately the size of a coin at arm's length. Outside this region, the image that the eye perceives is largely blurry and colourless.

Researchers at MIT, Cohen et al. explain in a paper that most of our visual perception is focused on the “big picture”. They point out many experiments in which people were very much surprised by the limits of their own cognitive experiences.

The brain does capture some details; however, it is hardwired to quickly and mainly take in the large objects and scenes, in order to get the gist of things.

We are not necessarily aware of everything in front of us…at least not consciously.

Once we notice the big things, our brain fills up the gaps with its own information.

Dr. Teufel, at the Cardiff University, points out that the neurons in our eyes respond to small, local patches of information. Our brain organizes this patchwork into a coherent percept.

Since we don’t really see everything in the scene that we look at, there is a level of ‘perceptual uncertainty’. We learn to acquire internal models of our environment, to deal with this uncertainty.

These internal models are made up of our past experiences, beliefs and expectations. The brain uses these to create the visual that we believe we are seeing…not simply what passes through our eyes.

And often we begin to trust these internal models, more than the real thing out there.

Ehinger and his colleagues, at the University of Osnabrück in Germany, have shown through experiments that in certain situations, the brain trusts its own generated information more than what it sees outside in the world.

When people look at something with strong expectations, they often see what they expect.

Karl Friston, a neuroscientist at the University College London, calls it ‘predictive coding’. He suggests that our brain actively predicts what input it will receive, rather than just passively processing information as it arrives.

The world around us is too overwhelming, for our limited physical abilities to gather and process all the information in real time. Thus, our brain continuously anticipates what it might observe. This enables us to get a quick sense of what’s happening…even if it may just be a good guess.

Another neuroscientist from the University of Glasgow, Dr Lars Muckli, further explains that brain’s main function - that it has evolved to do - is to minimize surprise.

Choose to be surprised

To anticipate and expect, helps us survive.

However, the juice of life flows beyond what we can conceive. To get there, we must strive to shed what we carry.

Not what to do
Nor, what to deny
Not to figure how
Nor, to know why

To keep the scene
At its peace, with magic
In silence, in stillness
Discover…not decide

The stage is all you
From you, arises all
However it hurts
This too, shall realize

String the parallels
Forward, and back
Shun the thee, and
Smile at the tide.