How Random Noise Could Betray an Army's Outpost

New research 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, mossf@umsl.edu and Lutz Schimansky-Geier, Humboldt University in Berlin, alsg@summa.physik.hu-berlin.de, 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.)