A recent nature show about deer at one point showed side by side comparisons of a deer hiding in a thicket, one shot by normal light, one with infrared. In the former, the deer was essentially invisible until it moved, while is stood out clearly on the infrared.
Which clearly would be bad for deer, if wolves could see by infrared.
dofe beat me to it. Several varieties of Pit Viper have infrared sensding, but to call it “vision” is kinda pushing it. They essentially hyave an infrared pinhole camera with a HUGE pinhole, so that they can sense direction, but can’t really “image” with it.
Vampire bats apparently have something similar, with rough vision “pits”, and some insects seem to be sensitive in the IR:
this piece suggests that IR vision is too “noisy” to be useful. I suspect they’re not being clever enough in their imagining of possible IR viewing mechanisms, though – pit vipers “see” just fine, albeit in a limited way.
I wonder if it’s a coincidence that it’s primarily cold-blooded creatures that seem to have developed any form of IR vision. I imagine that with a warm blooded creature, a retina in a warm eyeball would be the equivalent of putting your light sensor in front of a spotlight and then trying to detect fireflies.
I don’t think this is it. For one thing, I think “warm blooded” is a misnomer and means that body temperature is regulated, whereas “cold blooded” is also a misnomer meaning temperature is unregulated. Cold blooded animals create body heat too.
For another thing, the sensing organ doesn’t have to be cool to tell that more thermal radiation comes from one direction than another. It only has to sense that the thermal radiation levels are different. It’s convenient to think that cold radiates too, even if heat radiates in a sense that cold doesn’t. This takes advantage of a principle in optics saying that, in many cases, you can figure the same things out whether you trace rays upstream or downstream. For another thing, the sensing organ can tell that it’s radiating heat in some directions and not others, if most of the environment is cool and the detected object is at the same sense as the sensing organ.
I suspect that the stereo is for purposes of improving their effective resolution. Move your head until your target shows up in both pits, and then it’s dead ahead of you. It might be interesting to experiment with pair of sources on either side of a snake, to see if it confuses them into attacking empty air.
Educated WAG: I think it’s because it’s all relative. A warm food animal is just much warmer than the surroundings. Made up numbers: animal is 30 units, average of no animal view is 1 unit. But if the snake is warm blooded, the view is 26 units and the prey is still 30. It’s still more than everything else, but the ratio is so even. Also, I don’t it wouldn’t be out of the blue (although I don’t know any research) to suggest that the snake adapts and “cleans up” the noise by lowering the gain or something, so that on a warm day where the snake is warm, the ratio differences are still large. It’s like if originally the heatmap signal was red on orange, and you shifted it so that it was slightly less red on blue or yellow.
Differences, or ratios here too, yeah, probably why they are paired organs. Are you saying like if the left gets an average warmer signal than right, it follows that there is a heat source, maybe prey, to the left? Makes sense. This is vaguely analogous to source localization in hearing. And what Chronos is saying.
To “see” in infrared, the radiation from the hot object must be heating your sensor, and this signal has to be distinguishable from heat coming in from every direction through conduction in a living organism.
Heat conducts better than it radiates in most materials, and a living body using earth life has a lot of sources of thermal noise - the pulsatile flow of blood is one example.
It just may not be possible for nature to create a good enough sensor and do the necessary signal processing to detect infrared in this situation. Those pit vipers have body temperatures that are much lower, and their prey are hot, relatively speaking.
In herpetology lab we did an experiment in which we “blindfolded” a tree boa by putting tape over its eyes (they don’t have eyelids, but instead have a hard scale over the eyes) and then tested its infrared sense by moving a water balloon filled with warm or hot water around its head. We recorded how far away the balloon was at the time the snake oriented toward it. They had a good directional sense, with the greatest sensitivity above and below the horizontal plane. IIRC, they were able to orient to a balloon that was mammalian body temperature more than a meter away.
Yes, I’m saying this, and more. I gather that each pit in pit vipers does not just give a more-or-less signal. The snake senses what region of the pit gets more signal than what other signal. Like CalMeacham said (and I think he’s our most expert expert in optics), it’s a pinhole camera, just a very crude one. I think it’s more analogous to seeing than to hearing, in fact I see that that pit is an early stage on the evolutionary path to an eye. I wonder where evolution might take it. Could those evolve into eyes with sharp vision? What would the lens be made of, to be transparent to thermal radiation – perhaps something like chitin? Would it be full of air? Marvelous.
IR has a greater wavelength than (human-)visible light, and there are limits on how sharp an image you could produce using IR alone. I think our thermal cameras already produce images about as sharp as this particular input allows.
Granted, that’s a useful enough acuity, just sayin’ it won’t match RGB.
If you’re interested in animals seeing EM radiation outside of our visual range, plenty of insects, birds and fish can see some of the UV spectrum, and the mantis shrimp can see both a much larger spectrum of light than humans as well as light polarization – it has 16 different light-sensitive pigments.
The wavelength does reduce the best resolution possible with a given aperture due to diffraction, it’s true - but only by a factor of ten or so. I think thermal cameras have poor resolution primarily because they use image sensors of way less than one megapixel. I’ve seen, I think, as poor as 0.02 megapixels. The sensors are spectacularly expensive compared to visible light image chips. Also, it’s not unusual for thermal radiation subjects to not have a lot of contrast, so the images may look less snappy for reasons unrelated to resolution but which give us a similar visual impression.
If you can’t get past the paywall at the above link, here is a summary from Ed Yong’s blog, including illustrations of colors we can discriminate, but that mantis shrimps can’t. However, what Yong says about how the shrimp actually do discriminate colors seems to me to fail to bring out one of the most interesting points in the actual article:
I think you are exaggerating, incidentally, in saying that mantis shrimp can discriminate “a much larger spectrum of light than humans”. Like the birds, fish, and insects you mentioned, they can see a small way into the ultraviolet, but most of their light sensitive pigments are sensitive to wavelengths within the range of (humanly) visible light.
They are remarkable animals, but perhaps not quite ready to be our new stomatopod overlords.
Many sea creatures have crappy color vision. Some octopuses and cuttlefish have very elaborate camouflages (checkerboard), yet are color blind (monochrome?).
I think mantis shrimp cone types depend on the species. I don’t know if I read it or assumed, but I feel like the peacock mantis shrimp (i.e. the pretty one that gets all the photo ops) has more cone types than the dull beige ones.
Yeah, you can say that a deer has “UV cones,” but it really means is that they have cones that go farther into UV than ours, but still see mostly blue. Human’s UV detection is limited not just by cone peaks, but like IR by their physiology as our lens filters a lot of UV out.
They’re not interested in being our overlords because that implies rule. They just want to murder all of us by club or by spear (have you seen them hunt!?)