Human memory limits

The details in the face are based on common Japanese characters. That is not a very effective way of remembering faces, I suspect.

Human recall is far more limited than we usually think. There are variations, which roughly follow IQ, and a few puzzling exceptions. But overall, most of us can only recall a few tens of thousands of facts, and this does not change after we are grown up, until illness damages the brain. So while you learn something new, you forget something old. (OK, you would probably forget something old even if you learned nothing new, but there is a diminishing return at least.)

Why does it not look that way? I will highlight two reasons why we can and should keep learning anyway:

1) Recall vs recognize.

While there are fairly narrow limits to what we can recall, we can recognize much, much more. A great example is the difference between active and passive vocabulary. An ordinary person uses only a few thousand words over and over. If you record everything they say over the course of a week, it will increase only slightly by expanding the time frame to a month. And if you record them again a year later, they still use the same few thousand words. The exceptions will be words that are used by others in the conversation, or that they have just read or heard in some source material they discuss. These words disappear out of the vocabulary again almost at once. In non-work English, 2000 words will cover over 95% of the speech! To not be outed as a foreigners, you will need at least 5000 though. (For instance, I would be outed as an alien if I started discussing female clothing in any great detail. Well, actually I am outed as an alien if I try to discuss these in my native Norwegian too, but you get the point.)

In contrast, even with just compulsory education you will be able to understand tens of thousands of words, without effort or particular talent. Just before Alzheimer’s sets in, you may well recognize 100 000 words if you are an office worker, even if you don’t work in education. The degree of recognition varies, but I personally would say you have a word in your passive vocabulary if you react when it is used in an incontrovertible way. (<– The word “incontrovertible” is wrong here. I used it as an example. It is completely meaningless in the sentence where I used it. Hopefully you noticed this immediately if you’re an English speaker, even if you did not know it means “unquestionable, agreed on, absolutely certain”.)

So, there are tens of thousands of words that you can recognize but don’t use. This is the case with other knowledge as well. If you’re older than 30 at least, you should jump a little in your seat if you hear someone say “We should not forget the 6 million Chinese who died in Hitler’s labor camps.” Even if you missed school that day and have no interest in history, some facts are used so frequently that they leak into your brain. (Incidentally, some of the commonly known facts are doubtful or just plain wrong, but generally not those that relate to Hitler.)

Because of this “passive knowledge” which keeps increasing faster and for longer than the “active knowledge”, learning is still worthwhile. But I will show you an even better way.

2) Layers of abstraction.

When we are babies, every experience is new, every observation is unique. But soon we master the noble art of generalization. For instance, all people have faces. (Insert joke about faceless bureaucrats as needed.) Chairs are chairs and not tables. Doggies and horsies are different from each other, but all of them are animals. As the years go by, we acquire more and more such generalizations, but they also get more and more precise.

The more we study a particular topic, the more we are able to generalize correctly, neither too little nor too much. Having precise generalizations saves a lot of “disk space” in our mind. We don’t need to keep a list of each case, or of each exception to the rule. We can handle these units without thinking much about them.

A related topic is mental pointers. (This is not a commonly used concept. I will explain what I mean by it.) For instance, the human short-term memory has a hard time remembering more than 7 units such as digits. Here in Norway, the phone operators are getting a nice little extra income after the phone numbers were changed from 3+5 digits (area code and number) to 8 digits. This is just a little more than the average person can hold longer than they can hold their breath, and so a lot of people dial the wrong number. Back in the old days, people usually only called within their own area and the couple nearest, and sometimes to an area where they had lived before or had family. They remembered the area code as 1 unit of information, which made it easy to remember long enough to dial.

To take another example, my birthday is December 27, which in Norwegian usage is written 2712. Therefore if I come across a phone number that is 27122712, I will instantly remember it for months or years, even if it has no other virtue. It is only 2 pieces of information to me, while to you it is 8.

A chess newbie will be happy to remember how each piece looks, what it is called, and what moves it can make. These three different types of information are stored as one unit in his memory. (Physically they are probably stored very differently, but they are retrieved in one unit. If you say “rook”, a chess player will immediately know roughly how it looks and what moves it can make.) You would think that a chess grandmaster must remember an inordinate amount of information, or else calculate his strategy anew each time. However, interviews have shown that these people think in a different way. They have pointers to far larger concepts, such as whole openings and endgames, which are stored in their long-term memory as one unit. When something similar comes up, even if it is not identical, they only need to remember that which is unique about the variant.

Well, that should be enough for now. I have passed a thousand words, which are like 993 more than you can remember. I hope this entry has been of some use to you, even though tomorrow you will not remember what it was you read today. Possibly not even that you visited this site at all.

Take this for a parting gift: If we cannot remember everything, then we should strive to remember the right things.