You know hearing loss leads to dementia.. No wonder you can't remember his name.This is correct, except that it does not address anything above the 8K range, other than it mentions children can hear up to the 20K range.
It is ranges above 8K that affect the understanding as well. I got this info straight from the military doctor who actually discovered this. He worked at Wright-Patterson AFB at the time. Wish I could remember his name.