The Forgetting Curve

In psychology, there are seven types of named memory failure: persistence, bias, misattribution, absent-mindedness, blocking, suggestibility, and transience.

That last one, transience, refers to our brain’s tendency to forget things over time.

In the late-19th century, a German psychologist named Hermann Ebbinghaus conducted a series of studies—most of them on himself, which makes the results quite limited and suspect—in which he determined that there’s a consistent rate of forgetting, which, when plotted out on a graph, roughly forms a curve.

More recent research, which was (thankfully) conducted with more subjects, has been mixed on the matter, but studies that attempted to control for gaps in Ebbinghaus’ documentation (he didn’t provide terribly thorough notes on some aspects of his experiments, which may have contributed to previous failed attempts at replication) have shown that this curve is probably at least generally a real thing, though it will of course vary from person to person, and vary quite a lot based on what a person is trying to remember and the context in which they’re attempting to remember that thing.

That said, we now have a basic formula that tells us the general rate at which humans will forget things they’ve just learned, with the likelihood of full, correct recall diminishing rapidly: about 50% of new information we learn is forgotten within an hour of learning it, and 70% is lost within 24 hours.

There’s a huge distinction between types of learning, though; we’ll lose about 90% of what we learned via listening within three days, but we’ll lose only 8% (a 92% recall rate) of something that we learned through doing, three days later.

One of the big takeaways from this realm of inquiry, then, is that the way we soak up information matters a great deal, if we want to recall that information later.

We retain a lot more of what we learn via doing than listening or watching, though listening and watching at the same time seems to be far superior to just listening or watching, alone: we retain about 65% of what we learn by listening and watching with focus, three days later.

Probably the most effective means of staving off transience-related forgetting is what’s called spaced-repetition learning, which means reviewing something you’ve recently learned so as to tell the brain, hey brain, this is important, store it away in my long-term memory instead of forgetting it.

Research has been mixed on the exact right formula for optimal spaced-repetition learning, but revisiting recently learned information shortly after learning it (within the first day or two) and then regularly over time, with more time in between each revisitation, seems to work best for most people.