We see things and hear things in quite different ways.
We have two ears so we can sense the direction from which sound emanates. And each ear has two dimensions of hearing. What do I mean by that? Well the first dimension is loudness and quietness. The second is pitch.
As a pure sound tone increases in frequency we detect the sound as changing ‘pitch’. But a pure tone at 440 Hz (‘concert A’) is not qualitatively different from a pure tone at 256 Hz (‘middle C’).
With light things are more complicated. Each eye gives us an image of the world but each small region within that image elicits an experience we call ‘colour‘. We have the experience of brightness which is akin to loudness. But the sensation of ‘colour‘ is quite different from the sensation of pitch.
As the frequency of an electromagnetic wave reaching a patch in your eye increases from:
- 400, 000, 000, 000, 000 Hz to
- 1000, 000, 000, 000, 000 Hz
..our sensation changes qualitatively. Let’s call 1,000, 000, 000, 000 Hz a terahertz (THz) so this range is from 400 THz to 1000 THz.
As the frequency increases, the light first elicits the sensation of red, then yellow, then green and finally blue and violet. All that has changed is the frequency of the electromagnetic wave, but our sensation has changed qualitatively: red is not just a ‘low blue‘: green is not a shade of red. These are a completely distinct sensations.
The reason is that at daylight levels of light intensity, each single frequency of light stimulates not one, but three ‘sensors’ (called cone cells) at each location. Simplifying considerably, each type of cell when stimulated individually elicits one of the three basic ‘colour‘sensations: red, green or blue.
As the frequency changes each of the three sensors is excited to different extents, and our overall sensation of ‘colour‘ at each location in the image is a combination of the three qualitatively different basic sensations.
But what if sound worked like that?
Well if our sensation of sound pitch worked in a similar way to our ‘colour‘ sensations: red, green or blue, then we would have 3 ears on each side of our head – or at least three sensors inside each ear. Let’s stick with the 6-ear idea because frankly it is more dramatic.
However each ear each would just respond to a single range of frequency. The ranges would have to overlap otherwise there would be some frequencies that would elicit no sensation at all i.e. we would be deaf to those frequencies. But stimulating each sensor would elicit just a single ‘note’ or ‘tone’ or ‘pitch’ no matter what the actual frequency. The notes would be a kind of audio-red, audio-green and audio-blue.
A single pure tone of sound would then elicit an audio-‘colour‘ depending on the relative stimulations of the single sensor within each of the three ears on each side of our head.
Now of course, this whole idea is nonsense. But it did strike me as interesting that we have evolved such distinct ways of seeing and hearing. On reflection one can imagine reasons why the different detection mechanisms might make sense.
- For light the range of frequencies we can detect ranges from 400 THz to 1000 THz. This is a ratio of just over a factor of two, and if these were musical tones they would cover only just over a single octave. And yet our sensation of colour can detect millions of distinct colours in this small frequency range, giving us phenomenal ability to discriminate between subtly different colours.
- For sound the range of frequencies we can detect ranges from 20 Hz to 20,000 Hz. This is a ratio of around 1000, or just under ten octaves. The sensor we have in our single our ear needs to have as wide a range as possible to let us hear the sounds around us.
Anyway. As Forrest Gump might have said: “That is all I have to say about that”.