The structure of Memory

Key memory stages

1. Encoding - info transferred into memory
2. Storage - maintenance of info
3. Retrieval - remembering info (recall vs recognition memory)

Multi-store Model of Memory 

Input -> Sensory Store (Iconic, Echoic) -> Short term store (rehearsal, coding, decisions, retrieval strategies) <- >Long term store (Permanent memory store)                                                - Output

 

Atkinson and Shiffrin (1968)

• Sensory store - brief holding of info, modality specific
• Short-term store - limited capacity, temporary
• Long-term store - unlimited capacity, near permanent

Assumptions:

• Info transferred to and form LTS through STS only
• STS and LTS and unitary
• The longer an item is held in STS. the greater the chance it will be transferred into LTS

Sensory stores

• Stimuli reside very briefly in sensory store
• This fades rapidly but info can be transferred to short term store by maintenance  and rehearsal
• Iconic store - visual sensory stimuli
• Echoic store - auditory sensory stimuli

Iconic store, memory lasts 0.5 seconds

• most influential work in this area by Sperling (1960)
• Brief presentation of rows of letters, read as many as possible
• participants could only report 4-5 letters
• Assumed visual info faded before most of it could be reported

Echoic store, lasts 0.2 seconds

• transient auditory store
• Auditory suffix effect

 

Short term store

• Limited capacity
• Material can only be maintained in store with rehearsal
• Unitary
• Info transferred to and from LTS through STS only
• The longer an item is held in STS, the greater the chance it will be transferred into LTS
• Immediate memory span is 7 plus or minus 2

The Brown-Peterson Paradigm

• If rehearsal is needed to maintain info in store, preventing rehearsal should impair memory
• Murdock (1961) wanted to measure the rate of decay from STS:
• Read either one word, three words, or three consonants (trigrams) to participants
• Count backwards in 3's for different duration of times
• rehearsal is necessary for maintenance of info in STS
• with enough rehearsal, info enter the LTS

Long term store

• has unlimited capacity 
• near permanent storage of info
• Unlimited duration 
• can remember info from years ago

Double dissociations - two tasks involve different stores if they are affected differently e.g. X performs normally on tasl A but poorly on Task B, Y performs poorly on task A but normally on task B

 

summary

STS 

- limited capacity - digit span plus/minus 7

- needs rehearsal - forgetting

LTS

- unlimited capacity and duration

- separate from STS - serial position effects and double dissociations

Problems for model

Patient KF:

• Impaired STS but normal LTS
• some normal, some impaired STM

Conclusions

Multi-store model very useful conceptually:

• Memory is not one whole entity
• 3 different sub-structures: SS, STS & LTS.

 A lot of evidence supports distinction between and within these structures:

• SS: info decays very rapidly, visual vs. auditory info
• STS: limited capacity, rehearsal required
• LTS: separate from STS.

Model problems:

- STS not unitary

- Impairment in STS doesn't always lead to impairment in LTS

- Model is too simplistic

- A better model is needed to explain the STS