Would light have octaves?
October 25, 2024 2:21 PM Subscribe
How about thirds, fifths?
If my envelope calculations are right, the frequencies of the edges of human light perception are not quite an octave apart (7.8e14s^-1 , 4e14s^-1). So maybe there are some animals that can see a full octave. Is there interesting interference, as there is with sound? If so, can we see it in smaller but rational ratios?
You might be interested in two-photon absorption.
posted by kickingtheground at 4:16 PM on October 25, 2024
posted by kickingtheground at 4:16 PM on October 25, 2024
Both sound and light are wave phenomena. But our ears and eyes work differently.
Our ears perform frequency analysis. That is, we can distinguish multiple frequencies; this is important in perceiving both music and speech. We can directly hear frequency interference, as you note.
Our eyes don't work this way. (Machines can do it— that's what a spectrograph is.) Rather, as Maxwell_Smart says, we have three kinds of detectors, each of which responds to a wide band of frequencies. The colors we perceive are blends of the inputs, losing the specific frequency information in the incoming light. That in fact is why you can see all the colors of the spectrum in a photograph, printed or digital, even though the photo only has three colors. So long as the proportion of frequencies is right, the wide range of frequencies in an actual scene will look the same as the three colors of the photo.
You don't see interference phenomena, because lights of different frequencies are just blended. E.g. shine red and green lights on a table and you'll see it as yellow.
There are animals with different frequency ranges— e.g. many birds and insects see well into the ultraviolet. Some animals detect infrared light. (By the way, there's no mystery about why we see the particular frequencies we do: those are the ones the sun churns out the most.)
posted by zompist at 5:05 PM on October 25, 2024 [9 favorites]
Our ears perform frequency analysis. That is, we can distinguish multiple frequencies; this is important in perceiving both music and speech. We can directly hear frequency interference, as you note.
Our eyes don't work this way. (Machines can do it— that's what a spectrograph is.) Rather, as Maxwell_Smart says, we have three kinds of detectors, each of which responds to a wide band of frequencies. The colors we perceive are blends of the inputs, losing the specific frequency information in the incoming light. That in fact is why you can see all the colors of the spectrum in a photograph, printed or digital, even though the photo only has three colors. So long as the proportion of frequencies is right, the wide range of frequencies in an actual scene will look the same as the three colors of the photo.
You don't see interference phenomena, because lights of different frequencies are just blended. E.g. shine red and green lights on a table and you'll see it as yellow.
There are animals with different frequency ranges— e.g. many birds and insects see well into the ultraviolet. Some animals detect infrared light. (By the way, there's no mystery about why we see the particular frequencies we do: those are the ones the sun churns out the most.)
posted by zompist at 5:05 PM on October 25, 2024 [9 favorites]
You may be interested in the line of purples and other non-spectral colors. The idea is that we perceive some mixes of light frequencies as their own color rather than hearing two frequencies at the same time as we do with eg two flutes playing thirds or octaves.
There are also fictitious colors that are things our cones can do in principle, but can't with any real spectral input of light. Some you can kind of see with gimmicks of inducing cone fatigue.
Anyway, colors and light are perceived differently than pitch and sound as described above, but non spectral colors are an example of an interesting vaguely chord-like perceptual interaction.
posted by SaltySalticid at 5:28 PM on October 25, 2024 [4 favorites]
There are also fictitious colors that are things our cones can do in principle, but can't with any real spectral input of light. Some you can kind of see with gimmicks of inducing cone fatigue.
Anyway, colors and light are perceived differently than pitch and sound as described above, but non spectral colors are an example of an interesting vaguely chord-like perceptual interaction.
posted by SaltySalticid at 5:28 PM on October 25, 2024 [4 favorites]
In addition to the perceptual aspects above --
3:2 and 4:3 are perceptually relevant ratios for sounds with harmonics at these small-integer ratios above the fundamental frequency. This is a lot of sounds, because of how strings and tubes oscillate. Light sources, on the other hand, don't tend to produce mixtures of that form.
posted by away for regrooving at 5:56 PM on October 25, 2024 [2 favorites]
3:2 and 4:3 are perceptually relevant ratios for sounds with harmonics at these small-integer ratios above the fundamental frequency. This is a lot of sounds, because of how strings and tubes oscillate. Light sources, on the other hand, don't tend to produce mixtures of that form.
posted by away for regrooving at 5:56 PM on October 25, 2024 [2 favorites]
non spectral colors are an example of an interesting vaguely chord-like perceptual interaction
Another way to think about this is to consider almost every colour to be chord-like in that almost any spectral input will stimulate multiple receptors, and think of different spectral mixes that yield equivalent receptor stimulation as loosely analogous to timbre.
We don't often pay much attention to visual timbre, because having only three receptor sensitivity bands (arguably four under certain illumination intensities if you count the rods as well), perceptions of timbre will be relatively subtle. We're starting out in much the same position as people with massive hearing damage who only have a handful of functioning hair cells left in each cochlea - they may retain enough hearing to discriminate pitch, but the timbre information that does things like carry the perceptible differences between vowels is no longer available, so they struggle to perceive speech intelligibly.
Given that colour perception depends so much on contrasts between reflection spectra coming back from the parts of any given scene, I would expect perception of visual timbre to be perceived as scene-global, correlated more with the spectral peakiness of the illuminating light than with the absorption spectra of specific objects within that scene. This might be a way to make sense of why fluorescent lighting feels harsher and more fatiguing than incandescent lighting or sunlight, for example. The speckly, shifting inteference patterns that show up in scenes illuminated by strictly monochromatic light sources like lasers might also be reasonably classed as a visual timbre effect.
posted by flabdablet at 8:16 PM on October 25, 2024 [5 favorites]
Another way to think about this is to consider almost every colour to be chord-like in that almost any spectral input will stimulate multiple receptors, and think of different spectral mixes that yield equivalent receptor stimulation as loosely analogous to timbre.
We don't often pay much attention to visual timbre, because having only three receptor sensitivity bands (arguably four under certain illumination intensities if you count the rods as well), perceptions of timbre will be relatively subtle. We're starting out in much the same position as people with massive hearing damage who only have a handful of functioning hair cells left in each cochlea - they may retain enough hearing to discriminate pitch, but the timbre information that does things like carry the perceptible differences between vowels is no longer available, so they struggle to perceive speech intelligibly.
Given that colour perception depends so much on contrasts between reflection spectra coming back from the parts of any given scene, I would expect perception of visual timbre to be perceived as scene-global, correlated more with the spectral peakiness of the illuminating light than with the absorption spectra of specific objects within that scene. This might be a way to make sense of why fluorescent lighting feels harsher and more fatiguing than incandescent lighting or sunlight, for example. The speckly, shifting inteference patterns that show up in scenes illuminated by strictly monochromatic light sources like lasers might also be reasonably classed as a visual timbre effect.
posted by flabdablet at 8:16 PM on October 25, 2024 [5 favorites]
More on the "fictitious colors" idea, this demo of chimerical colors. Two minute video demonstrating effects. For instance "Stygian Blue" is the color you perceive if you oversaturate your eyes looking at yellow, then switch to looking at black.
It's not quite like how audio interference works to make octaves because it's not simultaneous, it's a time-based fatigue response in your visual receptors. But the result is a little similar to harmony.
posted by Nelson at 10:55 AM on October 26, 2024
It's not quite like how audio interference works to make octaves because it's not simultaneous, it's a time-based fatigue response in your visual receptors. But the result is a little similar to harmony.
posted by Nelson at 10:55 AM on October 26, 2024
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On edit, there are animals (like the mantis shrimp) that have sensitivity to far greater dimensions of the spectrum as well as to differences in circularly or linearly polarized light.
posted by Maxwell_Smart at 3:31 PM on October 25, 2024 [4 favorites]