Design of Everyday Things [41]
Long-term memory is memory for the past. As a rule, it takes time to put stuff away in LTM and time and effort to get it out again. This is how we maintain our experiences, not as an exact recording of the events, but as interpreted through our understanding of them, subject to all the distortions and changes that the human explanatory mechanism imposes upon life. How well we can ever recover experiences and knowledge from LTM is highly dependent upon how the material was interpreted in the first place. What is stored in LTM under one interpretation probably cannot be found later on when sought under some other interpretation. As for how large the memory is, nobody really knows: billions of items, probably. One informed scientist estimates the capacity as a billion (109) bits or about 100 million (108) items.13 Whatever the size, it is so large as not to impose any practical limit. The difficulty with LTM is in organization—in getting material in and in figuring out how to retrieve it—not in capacity. Storage and retrieval are easier when the material makes sense, when it fits into what is already known. When the material makes no sense, it will have to be worked on, structured, and interpreted, until finally it can be retained.
Human memory is essentially knowledge in the head, or internal knowledge. If we examine how people use their memories and how they retrieve information, we discover a number of categories. Three are important for us now:1. Memory for arbitrary things. The items to be retained seem arbitrary, with no meaning and no particular relationship to one other or to things already known.
2. Memory for meaningful relationships. The items to be retained form meaningful relationships with themselves or with other things already known.
3. Memory through explanation. The material does not have to be remembered, but rather can be derived from some explanatory mechanism.
MEMORY FOR ARBITRARY THINGS
Arbitrary knowledge can be classified as the simple remembering of what is to be done, without reliance on an understanding of why or on internal structure. This is how we learned the alphabet and how to tie a shoelace. It is even how we learned the multiplication tables, that 3 times 2 is 6, although for that we could refer to an external structure. This is how we are expected to learn arbitrary codes to operate the modern, misbegotten telephone system. It is also how we are forced to learn many procedures required of modern technology: “To load this program, put the floppy diskette into drive A and type ALT MODE, CONTROL-SHIFT-X, DELETE.” This is rote learning, the bane of modern existence.
Rote learning creates problems. First, because what is being learned is arbitrary, the learning is difficult: it can take considerable time and effort. Second, when a problem arises, the memorized sequence of actions gives no hint of what has gone wrong, no suggestion of what might be done to fix the problem. Although some things are appropriate to learn by rote (the letters of the alphabet, for example), most are not. Alas, it is still the dominant method of instruction in many school systems, and even for much adult training. This is how some people are taught to use computers, or to cook. It is how we have to learn to use some of the new (poorly designed) gadgets of our technology.
Most psychologists would argue that it is not really possible to learn arbitrary associations or sequences. Even where there appears to be no structure, people manufacture some artificial and usually rather unsatisfactory one, which is why the learning is so bad. For our purposes it does not matter whether