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Updated September 12, 2018

Forgetting: When Memory Lapses
[Hermann Ebbinghaus]A. How Quickly We Forget: Ebbinghaus's Forgetting Curve
  • Earliest studies of forgetting were done by Hermann Ebbinghaus (1885)
  • "nonsense" syllables (consonant-vowel-consonant, e.g., XOR, LIM, WEP, etc.).
Ebbinghaus (1885) Forgetting Curve

B. Measures of Forgetting

  • Retention: Proportion of material which is retained or remembered
  • Recall: Reproduce information without any cues
  • Recognition: Select previously learned information from an array of options
  • Relearning: How long does it take to relearn what you had previously learned?

C. Why We Forget

1. Ineffective Coding

2. Decay = memory traces fade with age. Not true except with dementia.

3. Interference Problem = forgetting information because of competition from other material
  • Retroactive Interference: New learning interferes with old learning (NIO)
  • Proactive Interference: Old learning interferes with new learning (OIN)
Interference in

4. Retrieval Failure
5. "Motivated" Forgetting

Freud two photos
  • Sigmund Freud (1901): Described a process he called "repression"

Franklin Case of Repressed MemoriesThe Repressed Memory Controversy
  • 1980s-1990s: Individuals began reporting to their therapists the recollection of memories, long buried from the past, which claimed experiences of sexual abuse, traumas, and even the witnessing of murder. These memories were considered to be "repressed" as Freud suggested.
Loftus at 2018
    • Elizabeth Loftus: research showing some false memories can be implanted
    • Estimate in experimental studies is 30% of subjects will develop a false memory and 23% accepted that they had an experience even though they didn't remember it.
    • a memory report can look like a genuine memory to observers, even if the person does not explicitly report remembering the events
    • PTSD patients show too many memories
  • Bottom line
    • abuse is more widespread than we used to think. 
    • "Repressed memories" are forms of "believed-in imaginings," that is, even if not factually true, the person reporting them believes them to be true
    • Therapists and others (e.g., police) need to be very careful not to suggest that there are buried memories

The Physiology of Memory I: Patient H.M.

Patient H.M. (Henry Gustav Molaison, 1926-2008)


Here's his story in a YouTube video [5'25"] from an animated TedEd presentation.
  • Short-term working memory was fine. He could remember things for 5 to 10 minutes.
  • He could not remember any experience longer than about 5 to 10 minutes, that is, anything that would be a new addition to his long-term memory. For example, he saw the same doctors and psychologist day after day, but never learned who they were.
  • He also had very significant memory loss of events in his life from before his operation.
  • His overall intelligence remained intact and he could generally care for himself, carry on conversations, and enjoy himself with puzzles and other games.
Hippocampus  H.M.
HM New
                Memories on Implicit Recognjition Test

This page originally posted on 9/26/07