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From: firth@sei.cmu.edu (Robert Firth)
Newsgroups: sci.misc,sci.physics
Subject: Re: differences between sound and light waves?
Message-ID: <4110@aw.sei.cmu.edu>
Date: 8 Feb 88 14:20:05 GMT
References: <413@prlb2.UUCP>
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Reply-To: firth@bd.sei.cmu.edu.UUCP (Robert Firth)
Organization: Carnegie-Mellon University, SEI, Pgh, Pa
Lines: 44
Keywords: macroscopic behaviour

In article <413@prlb2.UUCP> ronse@prlb2.UUCP (Christian Ronse) writes:
>As I am thinking about differences between vision and audition, I would like
>to know the difference of behaviour between light waves and sound waves which
>manifest themselves at our everyday (Newtonian, non-quantum) scale. For
>example: longitudinal/transversal waves, superposition and interference of
>waves, diffraction, refraction, reflection, and absorption of waves by
>objects. Don't explain me special relativity!

First, apologies for not having any references to hand - except Hal
Clement's 'Cycle of Fire', which has some aliens who "see" using sound
waves.

Both vision and hearing are sensitive over a wide amplitude range - vision
from magnitude +25 or so down to -7 or so; hearing from 120dB to a small
lower bound I can't remember.  In both cases, perceived brightness/loudness
is proportional to the logarithm of the amplitude; this is the Weber-Fechtner
law.

However, there are really major differences between how we see and how we
hear.  Some instances

(a) We can perceive barely one octave of visible light (4000..8000 A), but
    over 10 octaves of sound (15..20000 Hz)

(b) We can perceive the pitch of sound accurately, but have very imperfect
    colour perception.  For instance, we can't tell many colour "chords"
    from pure monochromatic light.

(c) Visual location uses parallax, by binocular vision.  Aural location
    uses phase difference, by binaural hearing.  We cannot perceive either
    phase or polarisation of light.

(d) We seem to have a far better linear memory for sounds than for colours.
    That is, we find it much easier to duplicate a sequence of tones than
    a sequence of colours.  Try that Simple Simon game both ways.  This may
    of course be learned rather than innate.

(e) Finally, of course, we can generate sounds as well as perceive them; we
    can't generate colours.

I don't know enough to speculate on the extent to which these differences
are necessary, given the nature of light and sound.  But note that some
creatures have a wider range of vision, can perceive polarisation, and
perhaps can perceive true colour "pitch".