No. 91: Jan-Feb 1994
It always comes as a surprise when we find supposedly primitive organisms employing our highly technical concepts; for example, the jamming-avoidance techniques of electric fish (SF#89). Still another potential example has been advanced: The lowly crayfish is now thought to enlist some of our sophisticated information theory.
Crayfish often live in noisy environments, where one would expect acoustical information transmission would be degraded. This would be true enough if linear information theory applied, but some, perhaps all, real situations are nonlinear. In such instances, information flow can actually be enhanced by the presence of optimized random noise. Stochastic resonance (SR) is the term applied in such cases of nonlinear statistical dynamics. J.K. Douglass et al write:
"Although SR has recently been demonstrated in several artificial physical systems, it may also occur naturally, and an intriguing possibility is that biological systems have evolved the capability to exploit SR by optimizing endogenous sources of noise. Sensory systems are an obvious place to look for SR, as they excel at detecting weak signals in a noisy environment. Here we demonstrate SR using external noise applied to crayfish mechanoreceptor cells. Our results show that individual neurons can provide a physiological substrate for SR in sensory systems."
Put more simply, the crayfish nervous system has the potential for cashing in on SR in noisy environments. However, the authors also remark that humans, too, accordingly to psychological experiments, seem to harness SR in the perception of ambiguous figures in noisy situations.
(Douglass, John K., et al; "Noise Enhancement of Information Transfer in Crayfish Mechanoreceptors by Stochastic Resonance," Nature, 365:337, 1993.)
Comment. In humans, then, and probably crayfish and other life forms, evolution via random mutation has just happened to hit upon a very sophisticated technique for improving communication!
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