Short-term memory

1. Short-term memory

2. Properties of STM • Capacity • Duration/Forgetting • Retrieval • Code type • Alternatives to Modal’s view of STM

3. Measuring STM Capacity: Digit-Span Task • Instructions: Recall the digits in the order presented. • Span Defined – list length that produces accurate performance on 50% of trials

4. Measuring STM Capacity: Digit-Span Task numbers • Digit Span Defined: # of digits accurately recalled 50% of the time • Standard Span: 7±2 digits • Modal Model Interpretation (Miller, 1956): • STM Capacity: ≈ 7 “chunks”

5. Chunking Demo CDHAOETGN C D H A O E T G N

6. Chunking Demo CDHAOETGN C D H A O E T G N

7. Chunking Demo CDHAOETGN C D H A O E T G N

8. Chunking • Chunking – “the process of combining information so that it takes up as little as possible of the limited space in STM” • Chunking  capacity • Why not a limitless STM? • “Chunk chunked chunks? • Required: • Chunking scheme • Time to apply scheme

9. Extraordinary Digit-Span: SF • Materials: • random digits • auditory presentation • Results: • After 45 days of practice: span = 83

10. SF: Digit Span

11. How did he do it? Chunk (and elaborated) groups of digits into running times (or historical dates)

12. Duration & Forgetting in STM • Brown-Peterson (1958/1959)Task: Initial attempt to measure duration of STM • Procedure: • Hear target set: 3 letters • count backwards for X s • recall target set • Manipulation – length of retention interval • Assumption: • Counting task eliminates/minimizes rehearsal • Measure of the rate of decay

13. Brown-Peterson: Main Finding • Initial interpretation: information rapidly decays from STM • Note: w/ 0-delay, only 80% accuracy.

14. A Test of Decay Hypothesis • Waugh & Norman (1965) – Decay or interference? • Method: • Auditory digit list (two speeds), followed by probe digit • TASK: name the digit that followed the probe in the list • Decay prediction: • Recall better at faster presentation rate • Interference prediction: • Recall equal for both presentation rates Slow fast Slow fast

15. Waugh & Norman (1965) Results: • Recall  w/ # of intervening items • consistent w/ both decay & interference • Recall (more or less) unaffected by presentation rate • Consistent mainly w/ interference

16. That was “retroactive” interference: Items that follow the to-be-remembered information interfere with remembering the earlier stuff:

17. That was “retroactive” interference: Items that follow the to-be-remembered information interfere with remembering the earlier stuff: e.g. if you have a psych and an english test in one week, if you study psych, then study english, all the english info will interfere with your memory for the psyc info. But there is a second kind of interference as well:”proactive”: Information that was previously studied will ALSO interfere with subsequent information you study.

18. Evidence for PI in Brown-Peterson Task -Keppel & Underwood (1962): re-analyzed Brown & Peterson’s data. Took a look at recall trial-by-trial, at various retention intervals Notice: on trial 1, 100% accuracy at ALL RI’s, only after 3 trials do you see substantial drops, which is more pronounced at longer RI’s

19. Wickens, Born & Allen (1963): release from PI by varying target stimuli -first three trials, target consists of letters, fourth is letters in control, numbers in “changed category” group

20. Side track: This issue of decay versus interference can be seen in other areas: e.g. Ebbinghaus’ serial position curve

21. Side track: This issue of decay versus interference can be seen in other areas: e.g. Ebbinghaus’ serial position curve

22. What might a “decay-based” perspective say about primacy/recency? (e.g. Atkinson & Shiffrin’s Multistore/modal model)

23. What would the “interference” camp have to say?

24. So who’s right?

25. So who’s right? These days, more evidence of forgetting based on interference than decay, although decay isn’t ruled out entirely, since it does have supporting evidence that an interference hypothesis wouldn’t anticipate (anterograde amnesics fail to show a primacy effect)

26. STM Retrieval/searching: 3 Possiblities • Issue: • How do we access information in STM? • Is Item X in STM? • Three possibilities: • Parallel – simultaneous access to all items. • Serial – consider 1 item at a time. Retrieval Models Parallel Serial Self- Terminating Exhaustive

27. Testing between these alternatives: The Sternberg Task • Set Size: 1 to 6 letters (well within limit for accurate memory in most people • Probe Type: • positive (in memory set) • negative (not it set)

28. Competing Retrieval Model Predictions

29. Sternberg Task: Results • RT  w/ set size Implication: serial • Negative = Positive Implication:exhaustive

30. Codes of short-term memory

31. Codes of short-term memory -semantic code

32. Codes of short-term memory -semantic code Wickens & Morisano (1972): release from PI by varying category of studied items

33. Codes of short-term memory -semantic code Wickens & Morisano (1972): release from PI by varying category of studied items -first three trials, target consists of fruit, fourth is fruit in control, other things in other conditions -varied the similarity of the new target to the old category

34. Codes of short-term memory -semantic code: Wickens & Morisano (1972) -visual code: Shepard and associates

35. Shepard’s rotational stimuli

36. A.

38. A.

39. 45

41. B.

43. B.

44. N/A

46. B.

48. B.

49. 110