On Thu, Sep 5, 2013 at 4:20 PM, Jeff Hawkins <[email protected]> wrote:
> Patrick, > I don't know what the equivalent would be for audition. The dynamic range > of any individual neuron is fairly limited, I think it is much less than > the > dynamic range you are able to perceive and detect. So distributed > representations are somehow making up for the limited dynamic range of > neurons. Well, there's a fascinating trick that the brain does with sound: You can express any waveform that you perceive as a single note as a bunch of sine waves of different frequencies played together - harmonics. We hear a 440Hz A-note from an oboe, but 880, 1320, 1760 and other higher multiples are there - so in fact, a, say, triangle wave can be decomposed into a list of sine waves of different frequencies. Those other frequencies are what make one instrument sound "brighter" than another. What is interesting is that you can actually *take away* the 440 - the fundamental note - entirely, but you will still perceive it to be there (I read somewhere that some speaker systems that have surprising bass in a small package actually synthesize *harmonics* of low notes that can't physically be reproduced, and our brains fill in the low frequencies that aren't actually there). So for most sounds, you're tickling things that detect a lot more than one frequency, and there's definitely some pattern recognition that allows for a set of harmonics minus the fundamental to let the brain perceive the fundamental note that's not there. -Tim
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