Short-term memory (STM) - Wofford .Short-term memory (STM) ... Fall 2010; N = 9 . Keppel &Underwood

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  • Short-term memory (STM)

    Chapter 5

  • Information-processing approach

    Sensory memory

    Short-term memory (STM)

    Long-term memory (LTM)

    Encoding

    Storage

    Retrieval

  • Short-term memory

    Questions Are STM and LTM distinct systems?

    How is information represented in STM?

    What is the capacity of STM?

    What is the duration of STM?

    How is information retrieved from STM?

    Method List learning

    Recall or recognition

    Immediate or delayed

  • You will see one number at a time. When I say Go, write down the numbers in the order you saw them.

    5

    2

    9

    1

    4

    8

    7

    3

    6

  • Answers

    5

    2

    9

    1

    4

    8

    7

    3

    6

  • Memory span

    Measure of capacity of STM

    General method Present increasing number of stimuli to repeat

    2 or 3 trials for each length

    Span is longest string of stimuli can successfully reproduce

    Tasks Digit span (Forward digit span)

    Alphabet span, Word span

    Picture span, Location span (corsi blocks)

  • Capacity of STM Gathercole (1999)

    Examine development

    of STM capacity

    Method

    Memory span

    Stimuli: Digits, words,

    spatial patterns, etc.

    Results

    Steep increase to 8yrs

    Gradual improvement

    until 12yrs

  • What is capacity of STM?

    Task: memory span

    Recall

    Capacity estimates

    Millers magical

    number 7 +/- 2

    Cowans model: 4

    items

    Why is there lack of

    agreement?

    Luck & Vogel (1999)

  • What is capacity of STM?

    It depends on

    Rehearsal rate Naveh-Benjamin & Ayres

    (1986): #s in 5 languages

    Type of information Verbal vs. visuo-spatial

    Chunking Create larger, meaningful

    units

    Knowledge (long-term memory)

  • Brown-Peterson task: Brown (1958); Peterson & Peterson (1959)

    What is duration of STM?

    Method 3-letter stimulus to remember

    3-digit number to count backwards (distractor)

    Results Forgetting curve

    Conclusion Information DECAYS from

    memory

    Due to passage of time

  • Brown/Peterson CogLab results

    Study trigram

    2s

    Count

    backward by 3s

    IV: distractor

    duration

    DV: accuracy

    New task

    version?

    Surprise test? Fall 2010; N = 9

  • Keppel &Underwood (1962) Analysis of Brown-Peterson task

    50

    55

    60

    65

    70

    75

    Block 1 Block 2 Block 3 Block 4

    3s delay% accuracy

    12 trials/block

    Finding: More trials -> worse performance Conclusion: Effect due to proactive interference (PI) PI: Old learning leads to worse performance on new info

  • What is duration of STM?

    Decay

    Info fades

    Interference

    Proactive interference

    Previously presented material interferes with new learning

    Retroactive interference

    Recent material interferes with older learning

    How do you separate influence of decay vs. interference?

    Blank interval = rehearsal

    Busy interval = interference

  • Waugh & Norman (1965)

    Hyp: Forgetting curve due to interference

    Method

    Probe digit task

    Heard 16 digits at rate of 1 or 4 per sec

    Same amount of items to interfere

    Differ amount of time (decay time)

    Repeat digit recall following digit in series

  • Waugh & Norman (1965)

    Results # intervening items

    reduces memory

    Conclusion Forgetting due

    interference not

    decay

  • Talland (1967)

    Examine nature of distractor task

    Method

    Brown-peterson task

    Distractor task: subtraction vs read answers

    Results

    Subtraction group did worse than reading group

    Conclusion

    Forgetting depends on type of interference

  • Sternberg (1966)

    Research question:

    How long does it take to retrieve info from STM?

    Measure speed of search process

    Method:

    Additive-factor method (repeat stage multiple

    times)

    STM scanning

    Memory set; probe y/n; DV: RT

    Possible results:

  • Search predictions

    Parallel

    search

    Serial

    exhaustive

    search

    Serial self-

    terminating

    search

  • Sternbergs (1966) findings

  • Sternberg: CogLab S09 data

  • Sternberg Results/Conclusions

    STM: serial exhaustive search

    Entire set is scanned whether or not match is

    found

    Scan rate = 38ms per item

    Size does matter!

    Why would a serial exhaustive search be

    more efficient than a serial self-terminating

    search?

  • Unanswered research questions still

    Is there a separate STM system?

    Same as sensory memory with rehearsal?

    Same system as long-term memory?

    What is the capacity of STM?

    What is the duration of STM?

    Are there other STM codes?

    Is there a distinction between verbal and

    visuo-spatial STM?

    Do they have different capacities?