Added Noise Enhances Ear Sensitivity

Biological Strategy

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Differentiate Signal From Noise

The environment surrounding any living system is full of signals, such as smells, sounds, electricity, magnetism, and more. Too many signals at once can be overwhelming, making it difficult to locate and react to any particular signal. To address this, living systems must differentiate among all signals, or “noise,” so they can focus on those they really need. During mating season, for example, male frogs gather close together in large groups to call for females. Despite their overwhelming, collective noise, females are able to find a particular male whose call is attractive to her. This is because the males use desynchronized calling, enabling individual recognition.

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Receptive organelles, or hair bundles, of the inner ear hair cells have increased sensitivity for signal detection due to added noise creating nonlinear stochastic resonance.

Image: Madhero88 /

Image: David Furness/Wellcome Images /

Used with permission from the Wellcome Trust, http://images.wellcome.ac.uk. License: UK CC-NC-ND 2.0. No cropping is allowed. A scanning electron microscope image of the sensory hair bundle of an inner hair cell from a guinea pigs hearing organ in the inner ear. Vibrations made by sound cause the hairs to be moved back and forth, alternately stimulating and inhibiting the cell. When the cell is stimulated it causes nerve impulses to form in the auditory nerve, sending messages to the brain.

Image: Gray's Anatomy /

“In this multicellular model for peripheral auditory coding the enhancing effect of Brownian noise on the high sensitivity of the auditory system was demonstrated. It was shown that the noise quantitatively accounts for the detection of weak pure tones which would otherwise either evoke receptor potentials too small to elicit spikes at all or too few spikes sufficient for determination of the stimulus frequency.” (Gebeshuber 2000:1865)