How much do we know?

The question here is not how much does humanity know collectively, or how much do we know about some given topic compared to how much we don't, or what portion of things can we reasonably say we "know" as opposed to believing or being "fairly sure" or such.  Those are all interesting questions, but what I'm after here is more literal.  How much does a typical human being know, by some objective measure?

To get the flavor of the question, it has been estimated that the average high-school graduate knows about 40,000 vocabulary items, or listemes.  A listeme is a word, word part or collection of words that you have to memorize in order to understand, as opposed to something you can understand by breaking it into parts you already know. For example

• There are two listemes in "listemes": listeme itself and the plural marker -s.  If you understand both of those, you can understand their combination [Or three: list, -eme and -s, if you're a linguist and familiar with morpheme, phoneme and such -- see below -- D.H.].
• Typical acronyms and such are listemes: USA or LOL, for example, even though the parts they stand for are well known, because you have to know which words the letters stand for.
• Idioms are listemes.  Knowing flying and saucer is not enough to know flying saucer.
• Proper names are listemes.  You have to learn that Muskegon is a city and that Michael Jordan is a former NBA player, even if you already know that Michael and Jordan are names.
• To some extent, different senses of words count as different listemes.  Knowing that you can eat off a plate doesn't tell you how to plate something in gold or what it means for a batter to step up to the plate.
• Listemes are somewhat subjective.  Someone well-versed in Latin might see intermittent or conjecture as made up of simpler parts, while for most of us they're one listeme each, and of course different languages have largely different listemes.

Each listeme binds a largely arbitrary sign to a meaning.  At a bare minimum, then, our typical high school grad knows 40,000 items, however much knowledge an item might represent.  Now, I make no pretense of knowing how the mind really represents such things, but the title of this blog is Intermittent Conjecture, so it seems that by a miraculous coincidence I've left myself room to speculate.

I would guess that typical listemes are associated with bundles of memories and their relations to other memories.   For example, plate might perhaps conjure up images of typical dinner plates and memories of eating and setting the table and such; images of plated items one may have encountered or a representation of the plating process; images from a baseball game with a batter in stance or a runner sliding into home.

Similarly to how words may be defined with other words, these bundles of images will typically overlap.  A memory of a dinner plate may include an image of a table, or of eating, making "something you put on the table" or "something you eat off of" natural, if incomplete, answers to "What's a plate?"

I've used "memory" and "image" fairly interchangeably here, but I suspect that the images that concepts are built on are nothing like fully detailed pictures or movies.  Rather, they're highly abstracted, with only the relevant features retained.

By this line of speculation, those 40,000 listemes might represent 400,000 or 1,000,000 or more images, grouped into concepts and with arbitrary signs attached.  There is much, much more to the picture, of course, but again we're just trying to get a rough estimate of what's in a typical brain.

Words are only one window into the contents of the mind.  We also know things we can't easily put into words, which one reason I had wanted to talk about different kinds of knowledge and formal vs informal education.  We learn to walk instinctively, and so it's much harder to characterize what sort of things one must "know" in oder to walk, yet if we can learn something, there must be some kind of knowledge involved.  Likewise for other skills like skiing or playing the trumpet, which we learn consciously and in many cases formally, but without necessarily learning a lot of vocabulary in the process.

We can also make associations unconsciously and non-verbally.  When the pioneer Lucky Bill in the post I linked to above looks off and sees bad weather brewing in the clouds, he probably doesn't have words for what he's sensing, but it's definitely something he's learned and knows, just as he knows how to let his horse know it's time to go.  This knowledge may well be built on the same sort of memories and images that we pin language onto, but it's not readily accessible to language.

If we take a mental image -- an abstracted memory -- as the basic unit of knowledge, with images grouped into concepts which may or may not have language attached, then it seems plausible that an adult human could have millions or tens of millions of such images.  We must also allow some capacity for storing the relations among the various images, concepts signs and so forth, but such "metadata" tends to be much smaller than the data it helps organize (see this post on the other blog for more on that).

Being a compugeek, the handiest objective measure of information I have is the byte.  Leaving aside that images may differ widely in size and taking an image to be on the order of a megabyte -- a completely wild guess which may well be off by orders of magnitude -- that would put our mental storage capacity on the order of terabytes or dozens of terabytes.

Until fairly recently, that was a lot of storage, but these days it's not a staggering figure.  As far as putting together something of the same order as a human brain, we may just now be reaching a necessary, but not necessarily sufficient, technological milestone.

I'm happy to learn that the wild stab in the dark given above turns out to be reasonably in line with other wild stabs in the dark.  See for example this Google Answers page (I didn't have a lot of luck tracing this back to the literature, but since it's all guesswork I'm not going to worry about it).