I thought that works because it creates a complex of sensations that overload your audio “tract”. For example if I do the described trick without isolating/covering my my ears with palms, it does nothing. The difference is not in pressure, but in the fact whether I can/can’t deep-hear the punches that my fingers create. Not a doctor, but something tells me there’s more to that. All scans shown that I have zig-zagged vessels in my neck, but within what they see as a “norm”.