Why Humans See More Colors than Dogs, but Fewer than Birds and Insects

Theoretical Physicist

“In the nineteenth century, with Maxwell’s Synthesis of the Laws of Electricity and Magnetism, physicists started to realize that what we perceive as light is deeply understood as a kind of disturbance of electric and magnetic fields.” Frank Wilczek says. “That gave us a new concept of the possibilities of perception of light, that show us we’re missing a lot.”

In fact, there is a lot to light that we as humans can’t see.

“What we perceive as color — what we perceive as light — corresponds to a very narrow band of frequencies, out of an infinite continuum. Not only that, but within that band we take three averages.”

These averages are made up of the three primary colors. These three colors mix and match to make up the rest of our field of vision, which is known as tri-chromatic vision.

“In computer displays, there are three different kinds of lighting elements used.” Wilczek explains. “When you see on your menu, the choice of millions of different colors, that doesn’t mean different lighting arrangements or possibilities. It means different combinations, different relative intensities of just three. Any perceived color can be synthesized from three basic colors.”

Not all animals have three cones of vision, dogs are known to have only two, while some other animals have more. These animals not only can see more colors than we as humans do, but can “sample” light in different ways than humans, such as infrared and ultra violet light. For now, in our current natural state of being, we can’t see them.

“Our perception of sound, in one way, is much richer.” Wilczek says. When a chord is played on an instrument, we are able to differentiate between the notes being played, we hear them as separate notes played at the same time. But when two waves of light, two colors hit each other, such as red and blue, we see them as one beam of light: purple.

“Our perception of that mixture is indistinguishable from a pure spectral yellow such as you’d see in a rainbow. It’s as if in music, when you play a C and a G together, instead of hearing a chord, you just heard the note E.”

This has a lot to do with how fast the waves oscillate. Sound waves are relatively slower, allowing our brains to keep up with the way they move, while light waves oscillate faster.

“The way we process that is quite different, it’s an all or none process where photons get absorbed and trigger changes in the structure of proteins. We have three kinds of proteins, and three different kinds of cone cells, that give us three kinds of average responses. And that’s why you can synthesize any perceived color with just three.”

  • Transcript

TRANSCRIPT

Frank Wilczek:  In the nineteenth century with Maxwell’s synthesis of the laws of electricity and magnetism physicists started to realize that what we perceive as light is deeply understood as a kind of disturbance, electric and magnetic fields. That gave us a new concept of the possibilities of perception of light that show us that we’re missing a lot. The electromagnetic equations permit radiation of any wave length and of any frequency – what we perceive as color – what we perceive as light is corresponds to a very narrow band of frequencies out of an infinite continuum. Not only that but even within that band we take three averages. We don’t sample all the different frequencies but just three averages. That’s called trichromatic vision. So for instance in computer displays there are three different kinds of lighting elements used. When you see on your menu the choice of millions of different colors that doesn’t mean different lighting arrangements, lighting possibilities. It means different combinations, different relative intensities of just three. Any perceived color can be synthesized from three basic colors.

Other creatures see less. Dogs, for instance, see only two kinds of colors like color blind people see basically only two kinds of colors. Other creatures see more. Other creatures – many insects and birds see four or five colors. They also sample kinds of light, kinds of electromagnetic radiation that humans don’t see. There’s infrared radiation. There’s ultraviolet radiation. Maxwell’s equations which describe light also describe radio waves and microwaves and x-rays and gamma rays. So all those things are possible forms of vision that human’s natural endowment doesn’t tap into. But it’s out there. On the one hand it’s very important to make concepts visual because it taps into very powerful methods of processing that we have. And on the other hand scientific knowledge of what light is shows us that our natural perception leaves a lot on the table and so it leaves us with the program of doing better with telescopes, microscopes, spectrometers and other kinds of gadgets that I’m developing for everyday life that will allow us to see more colors.

The human perception of color is limited really by the principles of quantum mechanics. It’s interesting to compare the human perception of color to the perception of sound. Our perception of sound in one way is much richer. When you have two pure tones together like a C and a G, a simple chord that’s a fifth. If you hear that you can hear the separate tones even though they’re played together and you hear a chord. You can also sense the separate tones and if one is louder than the other you can continuously judge how their relative intensity. Whereas with colors if you mix two different – if you have two different colors say spectral green and spectral red and mix them what you see is not a chord where you can see the distinct identities preserved but rather an intermediate color. In fact you’ll see something that looks like yellow. The perception of color sort of throws away the detailed resolution, detailed accounting of the different kinds of underlying tones, different kinds of pure frequencies or pure colors that are underlying the perception. Our perception of that kind of mixture is indistinguishable from our perception of a pure spectral yellow such as you’d see in a rainbow.

It’s as if in music when you played a C and a G together instead of hearing a chord you just heard the note E, the intermediate note. On the other hand visual information is much richer in conveying the spatial structure of things. We get a detailed image whereas sound gives much poorer spatial resolution. And there are good physical reasons for those things. Sound waves are relatively slow – oscillate relatively slowly so that mechanical vibrations inside our ear and electrical processes inside our brain can keep up with them and so we can keep that kind of time structure. We can keep track of it. That’s why we do a good job with chords. Whereas the oscillations in electromagnetic radiation are very, very fast. Much faster than any mechanical system can keep up with or that nerve firings can keep up with. So the way we process that is quite different. It’s an all or none process where photons get absorbed and trigger changes in the structure of proteins. And we have three kinds of proteins and three different kinds of cone cells that give us three kinds of average responses. And that’s why you can synthesize any perceived color with just three.