Why We Forget

Just as there are different types of memories (and memory), there are different types of forgetting.

  • Trace Decay: This is when a memory fades away, as the winds of time sweeps any trace of its formation from the mind. A memory that isn’t rehearsed often enough cannot withstand the erosion of the months and years. (What is the name of the kid that sat in front of you in the first grade?)
  • Retrieval Failure: This is when a memory is simply lost in the dark deeps of the mind. It is still out there. The right cue, as a life saver tied during the formation of the memory, can pull it back to the shore of consciousness. (Who won the academy award for best supporting actress in 2000? What if I told you she is married to Brad Pitt?)
  • Ineffective Encoding: This is when some details are just not admitted and are left out in the cold without anyone noticing they are missing. Poor souls, they were unnecessary, superfluous or didn’t stand out enough to make the cut. (What is Mozart’s first name? What is on the back of a penny?)
  • Interference: This is when memories compete for the same reserved seat, maybe because both of them have a similar name tag or face. A stupid attendant, confused about the seating arrangements, might send any one of these away.
    If the attendant is “Proactive”, she will not disturb the memory that is already seated. (Have you ever found it difficult to recall the rules of a game because they is too similar to another an old favorite which you play regularly?)
    If the attendant is “Retroactive”, she will prefer letting the new memory sit in favor of the old one. (Have you ever forgotten how to play a game because you tried out another game more recently?)
  • Motivated Forgetting: This is when you (“Supression”), or your unconscious mind (“Repression”), do not want a memory to stay. They are too painful, sad, shameful or disgusting to keep around and so are banished to hopefully never show their ugly faces ever again. (“What happened? I don’t want to talk about it!”)
Icons by Noun Project (Nicky Knicky, Christoph Robausch, Kristen Gee, Lorena Salagre, Gabriel Ardiles, Plainicon, MD Delwar, Vivian Ziereisen, Lemon Liu, Edward Boatman).

Different memories are resistant to different threats of forgetting. Some are very distinct over others (“his designs are so special you can never mistake them for someone else’s”). Some are very strong emotionally, even physically (“the water was freezing cold, you’ll never drag me back to that lake”). Some are acquired properly, such as after (not before, as some suggest) a healthy sleep and in a low stress environment (“can you please keep it down? I’m trying to study!”). Some are crucial for us (“it’s like my first phone number is branded into my brain”), and some are often in context (“c’est la vie, and I don’t even speak French”).

Yet the dreadful “Ebbinghaus Forgetting Curve” awaits even the most persistent. It shouldn’t come as a surprise that the longer the time period between a memory’s formation and recalling it, the higher the likelihood of it being forgotten. Memories must be nourished in order to survive. However, what might be surprising is this:

  • The relationship between the time period and the likelihood is not linear. It is a curve. At first, the chance of remembering drops down dramatically. This chance levels off as time goes by, which means that old memories rest in a retirement community where they all age in a similar slow pace.
  • This curve is can look very differently when a memory is recalled, even once. Reminders not only resuscitate memories, they make them more resilient. Better yet, repeating them continues to flatten the curve. It shouldn’t be too frequent, though, as suggested by some findings. Which leads us to…
  • “Spaced Repetition” is the ultimate way to beat the curve. A rehearsal schedule of ever increasing time periods is the most effective method we know to retain information over time. Our friend Hermann Ebbinghaus is responsible. He discovered the “Spacing Effect” and the “Learning Curve” which are the archenemies of his own Forgetting Curve.

Distributing sessions of reviews properly in order to take full advantage of wonders of spaced repetition and maximize memory retention is now assisted by computers and algorithms. One of the leading programs to accomplish this is SuperMemo, which has been in development for more than 30 years by Dr. Piotr Woźniak and his colleague Dr. Edward Gorzelańczyk.

Read my interview with Dr. Woźniak here.