Perception of infrasound: Difference between revisions

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In order to use infrasound for navigation, it is necessary to be able to localize the source of the sounds. The known mechanisms for sound localizations make use of the time difference cues at the two ears. However, infrasound has such long wavelengths that these mechanisms would not be effective for an animal the size of a pigeon. An alternative method that has been hypothesized is through the use of the [[Doppler shift]].<ref name="Quine 1981" /> A Doppler shift occurs when there is relative motion between a sound source and a perceiver and slightly shifts the perceived frequency of the sound. When a flying bird is changing direction, the amplitude of the Doppler shift between it and an infrasonic source would change, enabling the bird to locate the source. This kind of mechanism would require the ability to detect very small changes in frequency. A pigeon typically flies at 20&nbsp;km/hr, so a turn could cause up to a 12% modulation of an infrasonic stimulus. According to response measurements, pigeons are able to distinguish frequency changes of 1-7% in the infrasonic range, showing that the use of Doppler shifts for infrasound localization may be within the pigeon's perceptive capabilities.<ref name="Quine 1981" />

In early experiments with infrasound sensitivity in pigeons, surgical removal of the calumellacolumella, a bone that links the [[tympanic membrane]] to the [[inner ear]], in each ear severely reduced the ability to respond to infrasound, increasing the sensitivity threshold by about 50&nbsp;dB. Complete surgical removal of the entire [[cochlea]], lagena, and calumellaecolumellae completely abolishesabolished any response to infrasound.<ref name="Kreithen & Quine 1979" /> This shows that the receptors for infrasonic stimuli may be located in the inner ear.

==== Infrasound sensitive nerve fibers ====