Musical scales are exponential as well. (octaves are frequency doublings) There's also this experimental evidence about sensing loudness, weight, vibration, lightness, saltiness, thickness and several dozen other things. From: http://en.wikipedia.org/wiki/Stevens%27_power_law
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The general form of the law is
ψ(I) = kI^a
where I is the magnitude of the physical stimulus, ψ(I) is the psychophysical function relating to the subjective magnitude of the sensation evoked by the stimulus, a is an exponent that depends on the type of stimulation and k is a proportionality constant that depends on the type of stimulation and the units used.
The general form of the law is
ψ(I) = kI^a
where I is the magnitude of the physical stimulus, ψ(I) is the psychophysical function relating to the subjective magnitude of the sensation evoked by the stimulus, a is an exponent that depends on the type of stimulation and k is a proportionality constant that depends on the type of stimulation and the units used.