While I haven't looked it up, I'm quite aware of it. I'm also aware that some study suggested that humans might not intrinsically be able to recognize numbers higher than 2- apparently toddlers know of 1, 2, and "many." I'm curious if that's related, or if people just prefer things as simple as possible.
Well, there's also the fact (sort of) that the "normal" brain can only count up to 7 at a glance; similarly, memory for things you've heard (before being moved into long-term-ish memory) is seven seconds, while memory for images is 3-4 seconds.
The one-two-many theory is also corroborated by the "dual" tense in Old Church Slavonic and Arabic, i.e. there's I, We (two people) and We (more than two people) and so on, and so forth.
Actually, it varies depending on what form of memory is being used (and thus, what theoretical model you're working with, I guess...). Echoic memory has two forms - long and short storage. Short is the unprocessed auditory information and only hangs around for 1-2 seconds. Long is semi-processed and can last up to 5-ish. The more vauge sounding sensory memory (visual and tactile) hangs around for 1-2 seconds in its unprocessed form and I think yeah, 3-4 in its more processed form.
After that, it's apparently more a matter of rehersal/encoding which determines if you remember it or not. Not entirely clear on that, because I don't have my lecture notes here and the powerpoint slides are kinda vauge.
7 numbers is I think about right for numbers recalled in short-term memory experiments though, since it takes roughly 3-4 seconds to recite those numbers, at which point it's started to fade, so you forget the rest (the working memory buffer seems to actually be alot bigger, we just never really get the chance to encode it all before it evaporates). However, if you have time to reherse numbers and have a great encoding method (like
chunking), you can remember a potentially unlimited number of items. Kinda like those smartasses who memorise Pi up to 8,000 digits, most of whom use chunking, apparently.