Noise

Stochastic resonance is observed when noise added to a system improves the system’s performance in some fashion. More technically, stochastic resonance occurs if the signal to noise ratio of a nonlinear system or device increases for moderate values of noise intensity.

It was discovered and proposed for the first time in 1981 to explain the periodic recurrence of ice ages. Since then, the same principle has been applied in a wide variety of systems. Currently, stochastic resonance is commonly invoked when noise and nonlinearity concur to determine an increase of order in the system response.

Stochastic resonance has been observed in a wide variety of experiments involving electronic circuits, chemical reactions, semiconductor devices, nonlinear optical systems, magnetic systems and superconducting quantum interference devices (SQUID). Of special interest are the neurophysiological experiments on stochastic resonance, three popular examples of which are the mechanoreceptor cells of crayfish, the sensory hair cells of cricket and human visual perception.

Computationally, neurons exhibit stochastic resonance because of non linearities in their processing. Stochastic resonance has yet to be fully explained in biological systems, but neural synchrony in the brain, specifically in the Gamma wave frequency, has been suggested as a possible neural mechanism for stochastic resonance by researchers who have investigated the perception of subconscious visual sensation.

Stochastic resonance based techniques have been used to create a novel class of medical devices, such as vibrating insoles, for enhancing sensory and motor function in the elderly, patients with diabetic neuropathy, and patients with stroke.

A related phenomenon is dithering applied to analog signals before analog to digital conversion. Stochastic resonance can be used to measure transmittance amplitudes below an instrument’s detection limit. If Gaussian noise is added to a subthreshold or immeasurable signal, then it can be brought into a detectable region. After detection, the noise is removed. In this way, a fourfold improvement in the detection limit can be obtained.

Stochastic resonance is a generic phenomenon. It has to do with the fact that adding noise to certain types of nonlinear systems possessing several simultaneously stable states may improve their ability to process information. As such, it is at the origin of intense interdisciplinary research at the crossroads of nonlinear dynamics, statistical physics, information and communication theories, data analysis, life and medical sciences. It opens tantalizing perspectives, from the development of new families of detectors to brain research. From the fundamental point of view it is still a largely open field of research. Its microscopic foundations have been hardly addressed, its quantum counterpart needs to be further elucidated, and its relevance in complex transition phenomena remains to be explored.

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