Week 3 Short Term Memory and the Atkinson & Shiffrin Model
The basic structure and processes of the Atkinson & Shiffrin(1968) memory model
Components of the model
- Three Memory Buffers
- Control Processes which move information from buffer to buffer.
Sensory Information Store
- Basically unlimited capacity
- Duration @300 msec
- Forgetting -- Decay
- Code: Low level sensory features
Short term Memory (Working Memory)
- Limited Capacity: 7 plus or minus 2
- Duration @ 10 seconds if not rehearsed
- Forgetting--Interference
- Code: Primarily verbal/acoustic
Long term Memory
- Unlimited capacity
- Duration: Forever(?)
- Forgetting: Retrieval failure
- Code: Primarily semantic
Control processes move information from one buffer to the next
- Attention
- Maintenance rehearsal
- Elaborative rehearsal
The Sensory Information Store
The capacity of the SIS
- Sperling (1960) showed subjects a matrix of letters very briefly (50msec)
B K T U
Q X N C
F Z W L
- Subjects were asked to report all the letters that they could after this brief presentation. Ss averaged 4.5 letters
- Why? Two possibilities:
- SIS has a capacity limit of @ 4.5 items
- Information in SIS decays quickly and so all the letters can't be reported.
- Sperling's Partial Report Technique
- Assign each row of letters a different tone
- When tone sounds Ss only have to report that row
- Vary how quickly after the display the tone goes off
- Multiply by the number of rows to get capacity of SIS
- The results indicate that almost all the letters are available immediately but that the number of letters available decreases rapidly.
Capacity of Short Term Memory
George Miller and the Magic Number 7
- Digit Span Task: Number of digits that can be recalled in the correct order. (Normal adult can recall 5-9)
- Absolute Judgement Task: Presents sensory stimuli which vary in intensity & provides each intensity level a label. Subjects are presented with a stimuli randomly and asked to provide label. At @ 7 stimuli most subjects find this task quite difficult.
Chunking: Grouping stimuli to make them easier to remember.
FB-ITW-AC-IAIB-M
- De Groot (1964): Memory of chess players
- Expert and novice chess players are shown a chess board from the middle of an actual game for 5 seconds.
- Ss are then asked to reproduce the chess board from memory.
- On first try experts correct 90%; Novice correct 40%
- However, if pieces are randomly placed on board experts no better than novices
- Chase & Simon (1973)
- Measured latencies to place pieces on the board
- Pauses of over 2 seconds counted as a chunk boundary
- Players averaged between 5.3-7.7 chunks
- Conclusion: Experts don't have bigger memories than novices, they have bigger chunks.
Forgetting in Short Term Memory
Peterson & Peterson (1959): The rate of forgetting
- Subjects hear three letters (i.e. "C H J")
- Subjects hear a random number (i.e. "506")
- Subject counts backwards from number until they see a light.
- Upon seeing light subjects try to repeat letters
The Code in short term memory
Conrad (1964)
- Ss errors are not random.
- When subjects misreport items in short term memory tasks they tend to make errors which are acoustically related
If To-be-remembered item is E subject is more likely to report G than F
- This finding led early researchers to conclude that STM only operated with a verbal/acoustic code.
- Although acoustic codes may predominate in STM, other types of information (visual, semantic) can also be stored and manipulated in STM.
Errors in license plate numbers
Working Memory Model (Baddeley)
- Articulatory loop
- Visual-Spatial Sketchpad
- Executive Processor
Long Term Memory
Serial Position Effect
- Primacy Effect
- Recency Effect
- Rundus (1971)
- Postman (1965)
Detecting Malingering
- Faking Organic Amnesia--Why would someone pretend to have amnesia?
- To avoid responsibility
- To snag extra cash in tort cases
- Use very simple tasks that even amnesiacs should be good at
- Autobiographical Interviews
- Comparing equivalent tasks: Give two tasks that are just as difficult. Tell person that the second task is going to be much harder.
- Symptom Validity Testing
- Scoring worse than chance
- Pattern on subtests
- Serial Position
- Implicit Memory