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Decay and interference

Memory decay and interference affect our ability to recall information. Decay weakens neural connections over time, but re-learning can be quicker, showing some memory remains. Interference occurs when new learning blocks old (retroactive) or old learning hinders new (proactive). Understanding these processes can enhance memory retention strategies for medical students. Created by Carole Yue.

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Video transcript

We all know that our memories aren't perfect. As frustrating as it can be, we forget people's names, birthdays, and other things we'd like to remember. One reason forgetting happens is the very normal process of decay. When we don't encode something well or when we don't retrieve it for a long time, we become unable to retrieve it later. One theory about why this happens is that the pathway to and from the memory, meaning the neural connections between the cues and the memory, become weaker over a period of disuse, so it becomes harder to stimulate those neurons. This is sort of the classic use it or lose it problem. If you learned something once and don't ever revisit the memory, it's likely to decay over time. One interesting pattern of decay is that it seems pretty consistent, even for different types of materials. Your initial rate of forgetting is very high, but it levels off after a period of time. Back in the late 1800s, a German philosopher and psychologist named Ebbinghaus was the first person to really look at the decay in human memory. He made himself learn a bunch of three-letter nonsense syllables, and then he tested himself to see how much he remembered at different time intervals, from zero to 30 days. He found that his rate of forgetting was very rapid at first. If he remembered those words after a few days, however, then he generally remembered them for all 30 days. Later on, people replicated this pattern with different materials and over different time intervals. And they found that the more integrated the initial learning is, the more stretched out the rate of forgetting is, but it's still follows the same pattern. For example, if you study a language for a few years, then it'll take you more than a few days to forget it. Similar to Ebbinghaus's original forgetting curve, though, most of your forgetting will occur within the first few years of disuse. After that point, your forgetting will pretty much level off. The interesting thing about decay and forgetting is that just because you can't retrieve something doesn't mean it's completely gone from your long-term memory. Other than outright retrieval, one way we can tell if people have learned something before is by how quickly they re-learn that information or skill. So remember Ebbinghaus? In addition to forgetting, he studied re-learning with those same three-letter nonsense syllables. He found that even if he couldn't produce all the syllables from his list, it took him less time to learn the list the second time around than the first time, indicating that some foundation of the memory still existed, even though he couldn't produce it at the time. This foundation is called savings, because it's what saved in your memory, whether you realize it or not Re-learning works with procedural skills, too. For example, imagine that you learned how to play particular song on the piano a few months ago, but you can't play any of it today. Now I give you the music to that song and ask you to learn it again. If the inability to retrieve something meant that it was completely gone from your long term memory, then it would take you the same amount of time to learn the song the second time around. However it probably would take you less time to re-learn it than it did for you to learn it originally. This faster rate of re-learning tells us that you still have some information about that song stored in your long-term memory. Sometimes decay isn't the problem, though. It's that something else seems to be blocking our ability to get to the information we want. This experience is called interference, and there are two main types-- retroactive and proactive. Retroactive interference is interference that goes backwards, that is, some new piece of learning seems to reach back and impair your ability to retrieve something you used to know. For example, when you move to a new place, you get used to writing your new address on all the different forms and documents and stuff. And after a while of using this new address, you may find it difficult to recall your old one. In this case, your new address would be running some retroactive interference on your old address Proactive interference, on the other hand, is interference acting forward. Something you learned in the past gets in the way of your ability to learn and retrieve something correctly in the future. So I'll give you an example of something that happened to me a few months ago. I used one password for my email for a really long time. But then I had to change it. Sometimes when I log in, it's still hard for me to remember what my new password is, because all I can come up with is my old one. In this case, the prior learning up my old password is impeding my ability to remember the new one.