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I know 2 types of ears in the animal kingdom:

  • tympanal ears to detect the force exerted by air particles on a surface a.k.a. sound pressure (e.g. in mammals, birds, some insects, etc)
  • hairs/antennal ears to detect the particle-velocity component of sound through particle friction to free-standing hairs (e.g. in some arthropods, some fishes, etc.)

However, there are 3 types of artificial sensors (see this SE answer) which are used to detect sounds: pressure-based sensors (most of microphones), particle-velocity sensors (mostly on-going research) and particle-acceleration sensors.

Is there any organisms with ears which detect particle acceleration? If not, would there be a particular reason for not finding any in nature?

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For the inner ears of fishes (otocysts), particle acceleration (rather than particle velocity) is considered the transduction stimulus for sound detection. One of many examples of measured particle acceleration responses of fish ears is Radford et al. 2012.

For invertebrate groups like cephalopods and crustaceans, their statocysts (which vary in structure but are in many ways functionally analogous to otocysts) are also generally thought to act as particle acceleration transducers. For an example in squid, see Mooney et al. 2010.

One way the acceleration vs. velocity sensitivity has been determined is by tests showing that a constant velocity stimulus does not elicit change in the discharge of neurons associated with hair cells (in the otocyst or statocyst) but a change in the acceleration does. For an example of this in an octopus, see Budelmann & Wolf 1973.

Hair cells that lie on the outer surface of the body (e.g. lateral lines of fishes, superficial hair cells on crustaceans) can transduce velocity or acceleration depending on its surrounding structure. In fish lateral lines, superficial hair cells (more exposed on outer surface of skin) are generally velocity-coupled whereas those sitting in canals are acceleration-coupled (see Denton & Gray 1983). Whether lateral lines act in part as "ears" for sound detection may come down to semantics but I think they are worth mentioning here too.

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  • $\begingroup$ whaouuuu this unknown (to me) sensory world is really fascinating and exciting. I hope to hear more especially about crustacean and cephalopods hearing on this SE site in the future. Thanks for this overview! $\endgroup$
    – Noil
    Commented Oct 11, 2022 at 21:32
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    $\begingroup$ It is worthwhile to note that most so-called particle-velocity sensors measure particle acceleration and integrate. As Ian notes in order to qualify as particle-velocity sensor must generate a response for constant particle flow. I would be curious to learn, if lines of sensors act also s differential particle displacement sensor. Bending outer hair cells as function of particle flow qualifies certainly as particle-velocity sensor. $\endgroup$
    – WMXZ
    Commented Oct 13, 2022 at 15:51

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