Despite every source of information that I can find reporting that the feline cutaneous marginal pouch (Henry’s Pocket) has no known use or it has no use, my theory is that this interesting piece of cat ear anatomy enhances high frequency sound detection in order to more successfully locate the cat’s primary prey, mice and other rodents, which produce ultrasound (high frequency sounds).
There is nothing on the internet or the books I have which informs me why this strange pouch on one side of the ear flap exists so I have worked out a possible reason.
My curiosity was prompted by an email I received from Gene Sordillo:
Last year Philippa Jane Brown asked a question about the function of an external part of the cat’s ear. I have the same question about the small pouch located on the rim of the ear just at the base where the ear canal begins. It must have something to do with hearing, obviously, but is it possibly a device to amplify higher pitched sounds? My curiosity is getting the better of me. Thanks in advance.
I agree with Gene that it does amplify higher pitched sounds and it does it by attenuating (muffling) lower pitched sounds so the higher pitched sounds stand out.
How do I arrive at this conclusion, which is unsupported by science and I could well be wrong?
We know that some sound entering the ear hits the ear canal leading to the ear drum more or less direct while other sound waves bounce off the ear flap. This means some sound waves are delayed before impinging upon the ear drum. Sound entering Henry’s Pocket is further delayed because is bounces around the pocket before exiting.
This delay causes interference with other frequencies – interference effects – which attenuates the loudness of some frequencies of sound – “[the ear’s] geometry leads to interference effects that attenuate other frequencies” (source: http://interface.cipic.ucdavis.edu/ – Psychoacoustics of Spatial Hearing).
This is called a “pinna notch” meaning, I believe, that at a certain wavelength there is a blip in the sound (“pinna” refers to the ear flap, the bit you see).
The interference and subsequent reduction in the loudness of certain sounds leads to the accentuation of other sounds, namely high pitched sounds made by rodents thereby enabling the cat to detect with great precision the location of prey even when it cannot be seen. This aids survival, the reason for all evolution.
The cat has superb hearing and can hear frequencies as high as 65,000 cycles per second (or higher) a full octave and half higher than people. It is said that cats can detect frequencies from 55 Hz up to 79 kHz. Young mice emit alarm calls at 40 kHz while adult rats emit ultrasonic calls at 22 kHz 50 kHz, both detectable by cats.
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