Fluency vs Stability

One of the useful concepts set forth by Dr Wozniak in SuperMemo is that of the Fluency (aka "retrievability") vs Stability of memories. Instead of just speaking of memory "strength", these components can be considered separately - and in long term procedural learning they come to the forefront of evaluation (i.e. when you are grading yourself on the execution of an item).

As simple procedural definitions of these concepts, we can say that:

1. Fluency is the "ease" with which you can execute a procedure properly, and
2. Stability is the amount of time you can go without practice, and yet without forgetting (in SuperMemo, this would be measured by the inter-repetition interval).

Fluency Analogy:
Imagine that your mind is a huge box, and that every memory is written on a flashcard in that box. To recall a memory, you have to take the right card out of the box. When you have finished with that memory you put the card back, but at the top of the box where it is easily accessible. Hence, anything that you take out often remains at the top and in close reach. Anything that you only use access rarely gets easily covered by many other cards. A memory becomes fluent right after you learn or recall it, because it is right at the top of the box, and in easy reach. Anything that you have not accessed in a long time will not be very fluent, and hence hard to find. Therefore, fluency is related to how recently you accessed a memory - the more recently, the closer it will be to the top of the box, and the easier it will be to retrieve it.

Stability Analogy:
Imagine that your memories are buildings. As time goes by, some of the buildings fall down. Some remain standing longer, and others remain for less time. All of them lose their original lustre after only a few years of neglect. However, the ability of these buildings to remain standing is almost entirely a matter of materials and architecture. It is a matter of how they were crafted. Well crafted buildings that are made of strong materials (e.g. marble) can remain standing for thousands of years. To get those buildings back into their original glory is hardly near as complex and costly as to build them in the first place. All it requires is periodic maintenance.

Stable memories are strong buildings. Sometimes they need to be dusted off and glossed up (i.e. through a warm up session). Ultimately though, they can stand for long periods of time, untouched. Unstable memories are like buildings that may look fantastic, but will quickly crumble if not consistently maintained, due to their weak composition. If you use SuperMemo to extend your inter-repetition intervals as far as possible, you will soon find that every time you go to retrieve an old memory it will be like an old building, that you will have to dust off by warming up. That is, by practicing it several times to get your old skill back. As long as the warm up time is considerably less than the original learning time (e.g. 2 or 3 practices as opposed to several weeks of training), you can be confident that you have successfully retained your skill, as opposed to learning it anew.

So what is more important in grading - fluency or stability? Ultimately, you should always grade procedures on fluency. Ironically though, this is done in order to optimize their stability in the long term by choosing the right interval for the next repetition. However, it is fine to have a warm-up before grading yourself. This is done in order to take fluency to its maximum. If the memory is still there, it will come back to you within a couple of practices. If not, you will have to learn it all again and that will be much more painful!

Measuring Fluency:

Since your evaluation is going to be based on the level of Fluency, how do we measure this in practice?

One way is to ask yourself whether or not you'd get the execution right if you did it again. Another, is to take the average of a few attempts. For example, if you're trying to practice shooting a basketball into the ring from the free throw line, you will sometimes miss and sometimes get it in. The best way to grade yourself here is on an average of a few throws. However, separating your "warm up" attempts with your "real" attempt can be hard. Again, one you can ask yourself whether or not you'd expect to get it in if you threw it one more time.

As another example, consider the following exercise (remember that all use of declarative knowledge is a procedural activity!):

Q: 154 x 235
A: 36190

Suppose you were halfway through the calculation when you realised that you'd forgotten to carry the 2 in the first line. What should you do?

Firstly, you should go back and fix up the mistake, then continue the calculation that you started. Once you've done it, go back and do it a second time. If the second time is totally smooth you can comfortably grade yourself Good. If you did it fluently the first time you could obviously grade yourself Bright.

The difference between Good and Bright should not be the degree of fluency (they both should be your peak skill) but the amount of warm-up that is required to reach it. If you can't reach your peak after several warm up attempts, but you can competently execute it, then you can grade yourself Pass. Fail can be used when you get most of the procedure right, except for one or two parts that you keep mucking up. Finally, Bad and Null can be used in the normal sense.

The intuitive sense of fluency can sometimes be a hard one to get the hang of. However, it is entirely practical and compulsory for making the best use of the SuperMemo spaced repetition algorithm. Some good question to ask yourself are:

1. Was that a lot of warm up time?,
2. Did I execute it perfectly the last time?
3. Could I execute it perfectly if I tried again, straight away?
4. Did I have to think about it much, or was it automatic?

I will have to write more on the topic of "automatic" vs "conscious" execution of procedures. However, for now keep in mind that automatic is good - i.e. when you are fully fluent, you should be able to execute your skill without thinking about it.

Any questions or comments are greatly appreciated!