adds plausibility to the notion that living things make use of random
electrical noise to optimize specific behavioral responses. To test
this hypothesis of "behavioral stochastic resonance," researchers
have been studying the paddlefish Polyodon spathula, a primitive
creature whose fossil record extends back 65 million years.
Found only in
the river basins of the Midwestern United States and China's Yangtze
river, the paddlefish feeds exclusively on the zooplankton Daphnia,
a plankton 1-2 mm in length. Catching Daphnia mainly at the
bottom of silty waters where visibility is low, the paddlefish relies
upon electric-field receptors in its rostrum (a paddle-shaped nose-like
appendage) to detect electric signals emitted by the plankton, whose
swimming and feeding motions result in the firing of nerve cells.
In an earlier
experiment (Russell et al., Nature,
18 November 1999), researchers showed that adding an intermediate
amount of external noise in the vicinity of a juvenile paddlefish
could improve its ability to detect and capture plankton. Now, some
of the same researchers (Frank Moss, University of Missouri at St.
Louis, 314-516-6150, firstname.lastname@example.org
and Lutz Schimansky-Geier, Humboldt University in Berlin, email@example.com,
and their colleagues) have calculated that a swarm of plankton can
generate enough noise by themselves to amplify electrical signals
from a single Daphnia ordinarily too weak for the paddlefish
to detect, thereby betraying its presence and enabling the paddlefish
to detect and capture it.
This work adds
evidence to the idea that stochastic resonance has been adapted by
living creatures in their evolution, and makes progress towards designing
a definitive behavioral experiment to test this hypothesis. (Freund
et al., Phys. Rev. E, Mar. 2001; pdf version not yet ready
but we can fax the article to journalists.)