Listening deteriorates with age

[Shannon]

You are using the word listening when you mean hearing.

Conscious hearing changes with age, but this depends on the specifics of the reason for hearing deterioration. If the eardrum and/or some other portion of the ear cannot register the ultrasonic range after a certain age, it is because something has changed that no longer allows that to happen. Perhaps the eardrum changes, or the small bones in the ear are no longer as well lubricated, etc.

However, this refers only to conscious hearing. That is, hearing that relies on the nerves that serve the ear which allow you to consciously register the sounds.

If it was those nerves that were registering the subliminal for processing, you would be processing them at a conscious level and probably not getting very much out of them. Even though a 15 year old (for instance) can detect a 17 kHz sound, that does not mean they can actually comprehend speech at that pitch. My experiments show that the ability to actually comprehend speech is lost progressively as it goes above 10 kHz, and is almost entirely gone at 12 kHz, even though consciously detectable audio is present. Whether or not the subconscious can perform the rest of the comprehension, I don't know.

I do know, however, that the main input system for the ultrasonic subliminals seems to be not the standard nerves that serve the ear and result in conscious hearing, but the nerves that serve you in function of maintaining balance instead. Those nerves are wired to tiny hairs inside your ear which register movement of the fluids in your ear and the task of processing that data is passed directly to your subconscious.

Tiny things resonate best with tiny wavelengths, and so it makes sense that as you are young, your (smaller) eardrums would resonate better to very high pitches than the eardrums of an adult, which are larger. The size of the hairs in your ears, however, either does not change, or does not change enough to make a difference.

Therefore, if it is the hairs in your balance centers that are resonating to the ultrasonic audio, and in turn sending that data to your subconscious mind, which is in turn somehow processing it and comprehending it as speech, it would not matter if your primary hearing system and the nerves that serve it are affected by size or age.

To date, I have not found a better explanation than this as to why we actually sense and process ultrasonic audio in ways that allow us to understand it as speech.