Why can't I imagine frequencies outside of the range of my hearing?
April 4, 2013 12:14 AM   Subscribe

I can accurately imagine sounds of 440hz. I can imagine sounds of 880hz, 1760hz, and so on, and accurately identify octave intervals. Why can't I keep imagining sounds an octave up, until I am imagining beyond the limits of my hearing?
posted by Jon Mitchell to Religion & Philosophy (12 answers total) 14 users marked this as a favorite
Because when you think you are "imagining", you are actually just "remembering"?
posted by lollusc at 12:20 AM on April 4, 2013 [4 favorites]

Well, we could ask the same question about vision and colors: why can't we imagine colors that we can't see?

A possible clue with high frequency sound may be that we're increasingly bad at discriminating frequencies at the high and low ends of the scale. You may be able to identify intervals accurately around A440, but you probably can't do very well above 8,000hz or so. Since 12kHz sounds a lot like 16kHz (if you can hear that high and you're using a method that reliably produces sine waves that high), why would you expect 24kHz to sound particularly different if you could hear it?
posted by zachlipton at 12:51 AM on April 4, 2013

When you imagine sounds in the sense you mean I think you are imagining what hearing the sounds would be like. That is limited by the sensory equipment you've got; otherwise you're sort of imagining what it is like to be a bat, and we know what Nagel said about that.

You can imagine any sound you like in the abstract, so long as you don't have to imagine what it's like. That's a different thing but possibly the contrast between these two senses is contributing to your puzzlement?

Kudos to you for being able to imagine any notes distinctly outside an imagined tune - I can't.
posted by Segundus at 1:07 AM on April 4, 2013 [1 favorite]

The auditory cortex is what is imagining the sounds when you hear music in your head. The cortex is actually organized by frequency. Every frequency that you can hear is mapped to different cells in the cortex. Mappings for higher and lower frequency sounds simply don't exist in the cortex, so you can't imagine them, or at least you can't produce the internal sounds.

I suppose it would be possible to train the cortex to be able to 'hear' higher frequencies if you replaced your ears with some thing that had a broader range, but then I wonder if you'd simply have less precise discrimination between tones, because you only have so many neurons to use for hearing.
posted by empath at 1:09 AM on April 4, 2013 [9 favorites]

I can imagine very high and low sounds by extrapolation of pitches I have heard. I think you would be more likely to be able to if you played some series of tones and thought about the "rate" at which pitch changes and how you perceive that change (you do not perceive a change from a high C to a higher C as being as large as a change from middle C.)
posted by michaelh at 1:12 AM on April 4, 2013

Could you picture a color outside of the visible spectrum? How would you know what that sensation was, enough so that you could give it the name of a color?
posted by Blazecock Pileon at 1:15 AM on April 4, 2013

People are arguing about why this would or would not be surprising, but the reason for the phenomenon is the one empath gave. Basically, the human brain is in some ways staggeringly primitive, and sometimes doesn't seem to have got as far along the abstraction path as we might think. When you imagine a sound, you use the same parts of your brain as you would if you were hearing a sound; when you imagine moving your arm, you use the parts you would use to move your arm. These parts have been divvied up beforehand to mirror the world as you perceive it. What I think is interesting is that with this apparatus it is not possible to imagine sounds or colours outside the frequencies we can see and hear, but it is possible for me to imagine moving bits of furniture with my mind. They would all require different or impossible apparatus, and different mappings of the appropriate parts of the cortex, but one is possible and the other two are not. Why?
posted by Acheman at 1:51 AM on April 4, 2013 [2 favorites]

Could you picture a color outside of the visible spectrum? How would you know what that sensation was, enough so that you could give it the name of a color?

Strictly speaking, magenta is not in the spectrum. It's more a chord than a single note; like all the purples, but unlike any spectral colour, it stimulates both red-sensitive and blue-sensitive photoreceptors more strongly than green-sensitive receptors.

A pure spectral colour that stimulates blue and red receptors the same way magenta does would have to lie between their wavelengths of peak sensitivity, which would make it stimulate the green receptors even more strongly and therefore not look like magenta.

Photoreceptors can be deliberately fatigued by exposing them to intense monochromatic light. If you stare at something bright red for a minute or two, you will temporarily wear out your red photoreceptors; looking at something green before the red receptors recover will give you a colour experience that's greener than green.

It's also possible to feed each eye its own independent set of colour stimuli. Under the right conditions, the brain will combine these to produce impossible colours.
posted by flabdablet at 2:40 AM on April 4, 2013 [1 favorite]

There are two ways to conceive of "imagining X." The first is what you've done as you were typing out this question. You've posited the existence of X, a sound outside of the frequencies audible to the human ear, and thought about the fact that such a sound exists. Just like I could say, "imagine that humans had the power to fly," and your mind wouldn't necessarily jump to thinking about what you would feel like while you were flying, but would rather start thinking about the existence of human flight and how it might work and how it would fit in with other stuff we know about the world.

The second sense of "imagining X," is imagining what the experience of X would be like for you. And basically, there are two ways our brains do that. The first is through memory. If I say, "imagine that grass were purple," you'd remember what grass looks like from past experiences looking at grass and remember what purple looks like from past experiences looking at purple, and then you'd isolate those variables and try to create a picture in your head of what it would look like to combine the two. And when I say, "imagine the highest-pitched sound there is," what your brain is going to try to do is remember the highest pitched sound you've ever heard, because you have no sense memories to draw on to conceive of what the experience of a higher-pitched sound would be like for you. That's the limit of our ability to conceive of experiences, unfortunately.
posted by decathecting at 9:09 AM on April 4, 2013

I would guess it's because 'imagining' sounds, in the sense of hearing them inside your head, is tied to language, and those frequencies you can't imagine are outside the range language uses.
posted by jamjam at 9:11 AM on April 4, 2013

You might be interested in reading about David Hume's idea of the missing shade of blue.
posted by LobsterMitten at 11:41 AM on April 4, 2013 [2 favorites]

This is a really interesting question that I haven't encountered before!

Many people here are saying things like "when you imagine a sound, you use the same parts of your brain as you would if you were hearing a sound; when you imagine moving your arm, you use the parts you would use to move your arm." This might be right, but I don't think it's the whole story. It's a "simulationist" theory of imagination: we simulate an experience using the same cognitive machinery that we would if we were actually hearing something or other. But there are reasons to be skeptical that all auditory imagination must be like this. For instance, most of us can "hear" ourselves speaking in our heads when we think, in our own voices. What's strange is that our thoughts move at a far more rapid clip than we could hope to understand if we were actually hearing that speech. There's a weird paradox here. We hear speech in a compressed span of time, but we don't hear it as taking place in a compressed span of time.

Here's a possible explanation: we don't simulate a bit of of speech in our auditory cortex on fast forward speed, but we simply imagine that a proposition is true: "I am hearing blahblahblah." This, in itself, suffices for the experience or sensation. In other words, we don't actually need to "play" blahblahblah using our dedicated auditory mechanisms. Similarly, when I auditorily imagine a car alarm, it's enough for me to imagine "I'm hearing a car alarm." I don't need to actually set off the parts of my brain that would be firing if I were to hear WEE-OO WEE-OO. Yet, I have a WEE-OO WEE-OO experience. (To think that you actually need to "play" a WEE-OO in your head to have a WEE-OO experience is to fall into the myth of the Cartesian Theater.)

The bulk of the work on imagination has concerned visual imagination and mental imagery. Visual imagery is similarly often sparser than we realize. If you ask people to imagine what a cow looks like, they might do so, but then be surprised when you ask them what direction the cow is facing, or what color it is. They might not have considered. Similarly, you can visually imagine a chiliagon (a one-thousand sided polygon) without imagining each side. You can visually imagine a spotted hen without imagining each individual spot. Real pictures could not be this indeterminate. If our visual cortex needed to actually "draw pictures" in our brains, how could visual imagination be this indeterminate? Propositions can be indeterminate in the visual details, however. Perhaps it's enough for us to just imagine "I'm seeing a cow."

If you allow for the possibility of some visual and auditory imaginings being propositional in nature rather than simulated, it's really difficult to explain why we can't imagine sounds beyond the limits of our hearing. This is neat stuff.

Perhaps, however, your supposition is wrong. Maybe you can imagine sounds that high. Imagine the highest sound that you can. OK, now imagine something a little higher than that. Now a little higher. Does your imagination hit a limit? I'm not positive that mine does. (The Shepard tone suggests not.) And when I try, I think I can do it by doubling the pitch as well.
posted by painquale at 6:31 PM on April 5, 2013 [2 favorites]

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