PSY 101    [Psychology Images]   
Class 08: Memory II: Forgetting &
 The Physiology of Memory (Patient H.M.)
Updated September 12, 2021

Forgetting: When Memory Lapses
  • What would it be like if you remembered everything that ever happened to you?
  • It's probably helpful that we do forget all sorts of things that are no longer relevant of important
[Hermann Ebbinghaus]A. How Quickly We Forget: Ebbinghaus's Forgetting Curve
Earliest studies of forgetting were done by the German psychologist Hermann Ebbinghaus (1885) who developed lists of "nonsense" syllables (consonant-vowel-consonant, e.g., XOR, LIM, WEP, etc.). He learned lists of these syllables until he remembered the whole list. Then, he tested himself at different times to see how many of these syllables he could recall. His results showed a distinct pattern as the diagram of his "forgetting curve" below shows.
Ebbinghaus (1885) Forgetting Curve

  • Most forgetting takes place in the first hour or two after learning something. Then, forgetting becomes more gradual.
  • Later research found that Ebbinghaus' forgetting curve may be somewhat too steep, that is, not quite as much is forgotten as he found with himself.
  • Issue of remembering nonsense syllables vs. meaningful information: people have less motivation to remember nonsense information. Thus, for memorable information, we may retain that for longer periods of time.

B. Measures of Forgetting: 'Forgetting" can be measured in different ways. Here are 4 different measures of forgetting/remembering.

  • 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
    • Multiple choice tests favor recognition memory while fill-in-the-blank tests require recall memory
  • Relearning: How long does it take to relearn what you had previously learned?

C. Why We Forget

1. Ineffective Coding
  • If you did not really encode the information for storage in the first place, you can't recall it. This is a type of pseudoforgetting. Information which is processed at a shallow level is often not actually coded for memory.
2. Decay = memory traces fade with age
  • Research shows that, after controlling for ineffective coding, there is little evidence for decay in long-term memory in persons without dementia.
  • Note, however, that neurological problems like dementia do affect long-term memory
3. Interference Problem = forgetting information because of competition from other material (see examples in chart below)
  • Retroactive Interference: New learning interferes with old learning (NIO).
  • Proactive Interference: Old learning interferes with new learning (OIN)
Interference in Memory

4. Retrieval Failure = inability to remember at one point in time, but later on you recall what you were searching to remember. Probably reflects the absence of any effective cue to prompt the recall.
5. "Motivated" Forgetting

Freud two photos
  • Sigmund Freud (1901): Described a process he called "repression" when he found his patients recalling very painful memories from their childhood that they previously had "forgotten"
  • Repression is theorized to be an action by our mind in which distressing or anxiety provoking thoughts and feelings are hidden or buried in the unconscious.
  • Have you ever "forgotten" an appointment or meeting for something that you didn't really want to go to?
  • Many contemporary psychologists such as Elizabeth Loftus deny that most cases of such "repression" are real. Why? The majority of people who suffer from abuse or experience PTSD (post-traumatic stress disorder) actually remember their pain all too strongly. And, some patients may be responding to suggestions by a counselor or therapist to find memories that really don't exist.

The 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.
  • Parents, teachers, and others were identified as the abusers and some were tried before the courts and convicted.
  • As the years went on, multiple questions arose whether repressed memories actually exist and, if so, which of those reported were factual.
    • Elizabeth Loftus in 2018 at APAElizabeth 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.

Types of
Neuropsychologists and neurologists have seen for years that there seem to be at least two different kinds of amnesia, that is, an inability to remember what happened in the past, depending upon when some event like a brain injury took place.

  • Retrograde amnesia: an individual cannot remember details or experiences from before the event like a brain injury. ("retro" means "behind" or "in back of")
  • Anterograde amnesia: an individual cannot remember details or experiences after an event like a brain injury.  ("antero" means "in front of" or "after")
The event that may cause amnesia could consist of a brain injury like a car crash or a concussion or some other blow to the head. It might also have been an event like a surgery or an illness such as meningitis.

                    ObituaruPatient H.M. (Henry Gustav Mo
laison, 1926-2008) {W}

Patient H.M.

Henry Molaison (Patient "H.M.") experienced severe and frequent epileptic attacks. In 1953 a surgeon removed the hippocampus on both sides of his brain in the temporal lobes in order to treat him. Unwittingly, this surgery destroyed his ability to form new personal memories. He was studied until his death in 2008 and is considered to be the most important patient in 20th century neurology and neuropsychology.

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. hippocampus
HM New
                  Memories on Implicit Recognjition Test

H.M. was experiencing (1) massive anterograde amnesia and (2) significant retrograde amnesia. The destruction of most of the hippocampus and some of the surrounding tissue (e.g., entorhinal cortex, part of the temporal lobe) left him unable to form any new personal memories. He did appear to learn some new information (though in a rather hazy and unfocused way) about celebrities and people who became famous after his operation (see table on the right)

As researchers came to discover, however, he could still learn other non-personal skills like how to play different kinds of games or construct different kinds of objects with blocks, etc. This was the beginning of understanding the difference between declarative and procedural memory (see set of notes for next class for more about this).


O'Kane, G., Kensinger, E. A., & Corkin, S. (2004). Evidence for semantic learning in profound amnesia: An investigation with patient H.M. Hippocampus, 14, 417-425.

This page originally posted on 9/26/07