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 Miller s magical number 7 +/- 2 Cowan s 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 75 70 % accuracy 65 60 55 3s delay 50 Block 1 Block 2 Block 3 Block 4 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 selfterminating search Serial exhaustive search
Sternberg s (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?