Indeed, if you split up the signal in this way, you can do some remarkably processing. Its this color which is why a trumpet sounds different than a flute, even if they play the same note. Instead what we have found it its most valuable to take sound and basically split it up into a fundamental frequency and a sound 'color' which captures the associated overtone amplitudes. There's little advantage in being able to hear each frequency and then to do some heavy duty processing deeper in the brain. You always hear 440Hz mixed with others (such as 880Hz and 1760Hz), and the relative amplitudes of these frequencies are reasonably fixed because they're defined by physics. You never hear a 440Hz sine wave in the forest. Virtually all sounds we hear in the natural world have a harmonic character to them.

You can do a lot once you have individual sounds isolated from each other. If we try to read into it further, however, its worth noting that its useful to be able to identify 'individual' sources of sound. The way we hear sound and the way we hear light are the most effective ways we have found to deal with the signals. We evolved for maximum fitness (for some fitness function). The answer to any human perception question is 'its complicated.' there are thousands of sound receptors and they can all send signals at once so we can perceive many simultaneous sounds (with little spatial detail) but only one perceptual colour (for each region and with far more spatial detail). Colour is a complex thing synthesised from just 4 signals (roughly brightness + the three colours though brightness only matters much in low light). In short, colour perception is necessarily different to sound perception. This shows the brain is creating colour perception is a more complex way than 'averaging' would suggest. The brain doesn't average a signal containing red and violet light (that would average to green): it synthesises a new colour. The brain then synthesises perceived colours from these difference signals.Ī consequence of the complex processing is the ability to see non-spectral colours like magenta: a colour that never appears in a single wavelength spectrum. This is one reason for common colour blindness as, if the red-green receptors overlap too much, it bugger the ability to distinguish the two colours (completely missing receptors is a far less common cause). On reason is that the signals from the receptors are pre-processed to give pairwise differences between receptor signals (especially the red-green pair and the difference between the red+green and the blue).

But the overall process for colour is far more complex than averaging. Also, we would overload our optical nerve capacity if we tried to transmit a large signal containing data from all the pixels so a lot of pre-processing is done before the signal gets to the brain. Making sense of that in the brain isn't as simple as 'averaging' the signals. The reason is that the sensitivity of colour receptors are broad and overlapping. It is also possible to create colour perceptions that do not exist as single colours in any spectrum. It is not a matter of creating the perception of the mean frequency. Roger Barlow has already described why sound perception is different (you have enough receptors to distinguish bot a wide variety of notes and their strength at the same time).And the eye has only 4 receptor types.īut human colour perception is also different for another important reason. Colour perception isn't as simple as you think

Musical notes in a colorful wave