I can accept why the eye would have a lower limit to sensitivity to wavelengths too small to detect, but is there an explanation why the eye cannot detect wavelengths greater and greater than the red end of the spectrum? This puzzles me.
Might be the relationship to the size of the aperture?
That’s what she said.
Probably because they are not energetic enough.
Vision starts off as a chemical process. Presumably long wavelengths don’t have enough energy to initiate the process of phototransduction.
The width of the cells are within the parameter of the wavelength of visible light.
So, I guess they just receive, and don’t chat amongst each other, afterwards the visual cortex makes sense of it all the inputs.
I’m not sure why evolution never added infrared vision to the vertebrate eye; my guess would be that the lens simply absorbs too much of the infrared radiation to make it useful. (Infrared radiation, after all, has the nasty habit of making things heat up.) I’ll point out, though, that evolution has produced crude infrared sensing ability in snakes. The organs that they use for this look a lot like “primitive eyes”, such as those found in some molluscs. So maybe in another skillion years, snakes will evolve another set of eyes that can see infrared. Who knows?
It has to do with the wavelengths of light that can interact with the photo pigments in the rods and cones of the retina. Only a certain range of wavelengths will be absorbed by the pigments in a way that alters them sufficiently to initiate the vision process.
If I may ask, why does it make sense to you that smaller wavelengths are invisible?
Retinal ganglion cells (and the other retinal layers linked within). Followed by the LGN. The visual system generally increases in stimulus complexity as you go back, but that doesn’t meant that there aren’t any retrograde connections. Also, annular receptive fields in both areas are evidence that perception is built from the comparison of inputs from multiple cones/rods.
Humans never evolved infrared detection (or at least for a range subset of it) and snakes did because the latter are coldblooded. With us, most of the sensation would be noise from our own bodies.
UV is damaging to the eye, so the lens filters out that range of light.
Well, the ganglion cells do connect directly down the optic nerve to the brain. The ones that really make Jamicat wrong are the amacrine cells and horizontal cells, two layers of cells in the retina that interconnect the ganglion cells ,allowing them to influence one another’s activity. A lot of visual processing takes place in the retina, long before any signal reaches the brain.
The answer to the OP’s question is really just that we never happened to evolve that capacity. We might have been able to sense all sorts of things that we can’t. There is a large factor of random chance in evolution.
However, as has been said, seeing very far into the infra-red would be difficult because, as they are, the cornea, the lens, and the vitreous and aqueous humor that fill the eyeball are not very transparent to infra-red. It would not just be a matter of evolving suitably sensitive photopigments. Note that the snakes that can sense infra-red do not do so with their eyes, but with a simple pit, open to the air. Even they have not managed to evolve stuff to focus the rays, or to protect the sensory surface, that is transparent to infra-red.
I think this is the reason. Thermal imaging can’t see things cooler than the camera. For warm blooded humans, that’s almost everything.
All radiation has this habit. Infrared is in no way special in this regard.
Kind of off the beaten path, but…
If I hold a remote (the naked bulb kind) right up to my eye, and it’s dark enough, I can see the ir bulb glowing faintly red when I press a button.
What am I seeing?
Regular red light.
Is that scatter from the infra red, then?
You’re seeing IR. The eye can see it, just at a very low sensitivity. You can actually make “IR goggles” by using an IR bandpass filter and something like welding goggles to black out everything else. There’s enough IR in daytime sunlight to see the world in IR–it’s just that you don’t normally notice it because everything else is so much brighter.
The same is true of UV. I could easily see the (deep UV) laser when I was getting LASIK surgery. The combination of very bright light and having part of my cornea peeled away enabled me to see dim violet flashes.
I am sure I read somewhere that your range of colour vision changes if your lens is replaced with an artificial one, and that this is rather wider than the natural lens.
Great answers for OP (as well as all the others here). Never knew that about us all having IR vision.
Do they teach soldiers/special forces/survival techniques to cultivate this use of their vision when necessary? Or is that what we all do anyway once dark-adapted?
It’s pretty much what we all do anyway. But there’s not enough light at night for this to work–you really need to be blasting out the IR to see anything at all. The hacky IR goggles I mentioned can be somewhat dangerous for this reason; your pupils dilate to let in more light but almost all the energy from the Sun is still there. So looking at the Sun could be quite damaging even if it doesn’t look particularly bright.
There was a nifty Car Talk puzzler that hinged on the other side of this a few weeks back. The setup was that, just before D-Day, a group of soldiers were going in behind enemy lines to liaise with the French resistance. They crossed the channel on a moonless night, and a member of the resistance was supposed to signal them that it was safe to land, and they’d signal back. The signal was given and returned, but neither the Germans nor any of the young soldiers on the boat could see it. The only ones who could were the signaler on land and the grizzled veteran on the boat. The signal was a UV lamp–the signalers were both older men who had undergone cataract surgery, removing their lenses and allowing them to see the UV light that the young soldiers’ eyes filtered out.