Human Memory

There are three basic questions to ask about memory:

  • how are memories formed?  (encoding)
  • how are memories retained? (storage)
  • how are memories recalled?  (retrieval)

Encoding

  • encoding is an active process
  • requires selective attention to the material to be encoded
  • one question is at what point in the process is the distracting material screened out
    • early:  Broadbent (1958)  binaural v dichotic listening
      • binaural (2 messages but heard with both ears)...difficult to recall
      • dichotic (2 messages, one heard by one ear, other by other ear)...much easier to recall one message and ignore the other
    • however, cocktail party phenomenon suggests a late filtering:  all messages are registered but only the ones with meaning are actually put into memory
    • another possibility is that where the filter occurs depends upon the task:  the more attentional capacity that is available at any one time, the more one can use meaning and then the later input filter (selection) (Shiffrin, 1988).
  • memories may then be affected by the amount or type of attention devoted to the task of encoding the material
  • there may be different levels of processing which occur and that some are deeper than others, but there is no definition for what is meant by "deeper"
    • structural encoding (emphasis on the physical structural characteristics of the stimulus) is a shallow level
    • phonemic encoding (emphasis on the sounds of the words) is an intermediate level
    • semantic encoding (emphasis on the meaning) is considered deep processing
  • other aspects of encoding
    • elaboration=associating with other information
    • visual imagery can be used to add richness to the material to be remembered (also adds more sensory modalities)
      • see research by Paivio
      • then have two chances to remember something:  visual and verbal
    • self-referent:  make the material personally relevant
      • this requires deciding how the information is personally relevant

Storage

  • Over the years, analogies have been made to the new technology of the day to try to explain memory...current theories use a computer based model or information processing model
  • the most accepted model states that there are three stages of memory storage:  sensory store, short-term store, and long-term store.
    • sensory store retains the sensory image for only a small part of a second, just long enough to develop a perception
    • short term memory (STM) lasts for about 20 to 30 seconds without rehearsal of the information
      • with rehearsal short term memory will last as long as rehearsal continues
      • short term memory is also limited in terms of the number of items it can hold (see Miller, 1956)
        • capacity is about 7 items
        • can increase capacity by "chunking" (combine similar material into units)
      • originally short term memory was perceived as a simple rehearsal buffer but it turns out to be more complicated:  it is not limited to phonemic encoding, loss of information occurs by other means than simply decay and displacement, etc
      • perhaps short term memory is better modeled by the CPU of a computer;  it has the ability to store a limited amount of information in its cache ram while it processes it...a sort of working memory
    • long term memory has been suggested to be permanent:  that nothing is forgotten only the means of retrieving it is lost
      • supporting evidence includes the existence of
        • flashbulb memories:  vivid recollections of important events such as the death of JFK or the Challenger Space shuttle crash
        • Penfield's electrical stimulation of the brain studies
        • hypnosis aided recall
      • but these memories are not as accurate as once thought so perhaps long term memory is not permanent
      • so how does short term memory "stuff" get into long term memory
        • serial position effect
          • primacy:  perhaps this affects long term memory, first words get rehearsed more and thus can go into long term memory
          • recency:  words at end not rehearsed as often but they are still available in short term memory
        • so rehearsal helps get things into long term memory but there are different kinds of rehearsal:
          • maintenance rehearsal:  simple recitation
          • elaborative rehearsal:  meaning of the information is involved and this is more likely to cause shift into long term memory
        • organizational structures of long term memory
          • clustering:  related items are usually remembered together  (like chunking in short term memory)
          • conceptual hierarchies:  classification scheme used when possible to organize memories
          • semantic networks are less neatly organized bunches of conceptual hierarchies linked together by associations to other concepts
          • schemas are clusters of knowledge about an event or object abstracted from prior experience with the object (we tend to recall objects that fit our conception of the situation better than ones that do not)
          • a script is a schema which organizes our knowledge about common things or activities:  if you know the script applicable to the event, you can better remember the elements of the event

Retrieval

  • memory retrieval is not a random process
  • cues can help with retrieval
    • context cues:  perhaps it is the process of reinstatement of context cues that accounts for the helpfulness of hypnosis in recall
    • mood:  state dependent memory refers to the improvement in recall that can occur when the same emotional state is created as was present in the acquisition phase
  • memories are reconstructions (Bartlett, 1932)
    • schema theory and findings supports this notion as well
    • eyewitness testimony (Loftus, 1979) has shown that memories of an event can be changed by misinformation inserted into questions about an event (postevent misinformation)
  • perhaps some of the errors in recall are a result of failure in source monitoring (remembering the origins of the memories)
    • such errors happen often
    • may be responsible for reporting a memory as accurate eyewitness recall when it was something someone said ("gossip")
    • another version of this is "reality" monitoring:  did the event occur internally (thought or imagination) or externally (a perception of an actual event)

Forgetting

  • why do we lose memories?  it can be a problem with encoding, storage, retrieval, or some combination of these
  • Ebbinghaus (1885)
    • memorized nonesense syllables (CVC's) himself
    • he found that most forgetting occurs very soon after learning
  • however, when meaningful material is used, the forgetting curve is not so precipitious
  • measures used:  retention is the amount of material remembered
    • recall=subjects produce the information on their own (e.g., essay questions)
    • recognition=subjects identify previously learned information (e.g., multiple choice questions)
    • most research shows that recognition is easier than recall
    • relearning=look for savings in the second time of learning
  • theories of forgetting
    • ineffective intial encoding ("pseudoforgetting") usually occurs because of ineffective attention in the acquisition phase
    • decay:  forgetting occurs because memory fades with time (sort of like the effects of friction?)
      • but time is in and of itself is not a variable; it is only a medium in which processes can happen
    • interference: forgetting occurs because of competition from other information
      • retroactive interference=new information interfers with what has already been learned
      • proactive interference=old information interfers with what is being learned
    • retrieval failure=sometimes we can not remember something which at another time we can remember it; perhaps this is because of the context cues or retrieval cues present at the time
    • motivated forgetting:  we may tend to forget things that we do not wish to remember (Freud)

Repressed Memories

  • Freud long ago suggested that memories repressed:   repressed memories are those which for some reason the individual keeps in the unconscious
  • some people have suggested that memories which are "recovered" by therapists are memories which the therapists have created ("false memories")
    • could be due to problems in source monitoring
    • could be due to failures in memory reconstruction

Physiology of memory:  the search for the engram (the unit of memory)

  • biochemical theories
    • memory storage occurs in biochemical changes at the synapse
    • people with Alzheimer's show a depletion of acetylcholine and glutamate
  • neural circuit theories
    • there may be specific circuits in the brain for specific memories
    • there may be dendritic growth
  • brain injury:
    • anterograde amnesia (injury prevents new memories from occurring):  HM (Milner et al) memory loss probably due to damage to the hippocampus
    • probably other areas in the limbic system are involved too but these areas are most likely the site where short term memory is consolidated into long term memory
  • so memory is probably stored in the cortex, probably the sensory cortex appropriate for the sensory modality

Different kinds of memory?

  • implicit vs explicit:  prompting (giving clues or partial stimuli) will cause people with anterograde amnesia to remember what they had seen (implicit memory) ...explicit memory requires intentional recollection (when asked)  Are these different memory systems or just differences in retrieval ability?
  • declarative v. procedural
    • declarative = informational
    • procedural = actions, skills, operations (perceptual-motor)
    • memory for skills is largely unconscious and thus it might be related somehow to implicit memory
    • semantic (knowledge not tied to time) v episodic (knowledge tied to time when it happened) declarative memory

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Human Memory The Science

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Generic Long Term Memory memorization

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