Long Term Memory: Structure

short-term memory (i.e. working memory)

• active contents

  • Short duration→up to 20 or 30 seconds

  • Small capacity→7 +/- 2

  • Phonetic code→acoustic confusions

long-term memory

• No longer active; retrieved

  • Long duration→seconds to years

  • Large capacity→essentially no limit

  • Semantic code→semantic confusions

    • Memories about facts and information

serial position effect

primacy effect

• earlier items get more rehearsals

  • More likely to get into LTM

recency effect

• Last items still active in STM

  • Just get “dumped” out

H.M. (Henry Molaaison)

• Epilepsy, bilateral removal of hippocampus

• Intact STM

• Intact LTM before operation

• Inability to commit new information to LTM

Clive Wearing

• Viral encephalitis, swelling in brain damaged hippocampus

• Intact STM

• Intact LTM from long ago

• Inability to commit new information to LTM

Jimmie G

• Korsakoff’s syndrome: damage to the hippocampus

  • Intact STM

  • Intact LTM from long ago

  • Inability to commit new information to LTM

Patient K.F.

• Parietal lobe damage

• STM capacity of just 2

• Reduces recency effect 

• Functioning LTM

population dissociations

• No difference between populations on one measure, but a difference between populations on another

  • H.M., Clive, Jimmie: no difference between patients and non-amnesiacs on measures of STM; difference with LTM

  • K.F.: no difference with LTM, difference with STM

Implications of the neuropsychology of STM/LTM

• Separate brain systems

• One damaged system that is responsible for the deficient form of memory

• Second, intact system that is responsible for the normally functioning form of memory

explicit memory

declarative, conscious, and intentional

• episodic memory

• semantic memory

episodic memory

• personal events

  • Ex: Remembering your high school graduation day

semantic memory

• facts, knowledge

  • Ex: Knowing that Paris is the capital of France.

implicit memory

memory can occur without explicit awareness or deliberate retrieval

• priming

• procedural memory

• conditioning

retrograde amnesia

Cannot remember events before brain damage

• Can’t remember old memories

• General knowledge is usually better preserved 

• Memories from the distant past are usually better preserved

anterograde amnesia

cannot remember events that occur after the brain damage

• Can't form new memories

• Vague recollections

• Spontaneous productions

• Skill learning

• Indication that new learning has occurred

Warrington and Weiskrantz

• Examined potential new learning with verbal material

• different tests used

• participants were still comepleting words correctly even when they didn’t remember the word

• amnesic patients performed significantly worse than healthy controls on explicit memory tasks, but showed identical, normal performance on implicit memory tasks

  • explicit memory can act completely independent of implicit memory

direct memory test

• Directly refer to a past event

  • Subjects are instructed to use memory

  • Aware that using memory (explicit memory)

    • Free recall, cued recall, serial recall

indirect memory test

• do not refer to past events

  • No mention of memory

  • Simply ask to perform current task

  • Memory may be without awareness (implicit memory)

indirect memory tests types

perceptual identification

fragment completion

homophone spelling

perceptual identification

priming: information has gotten into your memory

fragment completion

Series of words shown but letters missing

• primed to fill in those letters correctly

homophone spelling

• Bear vs bare after showing a lot of “bare” words

• priming

general study method

jacoby and dallas (1981)

showed that varied levels of processing (e.g., visual, acoustic, or semantic analysis) significantly affected explicit recognition memory, but had no effect on implicit perceptual identification (priming)

• population dissociation

Converging evidence that shows that explicit memory and implicit memory involve different brain structures

Rely on separate, dissociable brain networks, supported by clinical amnesia cases, neuroimaging, and double-dissociation studies

• Population dissociations

• Experimental dissociations

• Developmental dissociations

• Drug-induced dissociations