Short-term working memory

1. Short-term working memory • Students of memory (e.g., James, Galton) have long considered that there is a memory system that keeps in consciousness a small number of ideas • William James referred to this system as primary memory • the primary memory is probably more closely related to working memory than to STM; this model will be discussed later on today

2. Short-term working memory • The capacity of short-term memory is traditionally measured using a memory-span procedure • in this procedure a participant is presented a sequence of items, and is required to repeat them back; start with one item, increasing the number of items by 1 until the participant begins to make mistakes

3. Short-term working memory • the point at which the participant is able to recall all items correctly 50% of the time is designated as her/his memory span • factors affecting memory span • auditory presentation leads to larger memory span estimates than visual presentation • rhythmic presentation is better than non-rhythmic presentation

4. Short-term memory • The next slide contains a series of digits. The digits are presented in pairs. Read the pairs of digits rhythmically aloud. Pause between each pair. For example, suppose the digits were • 24 89 17 14 29 12 3 • After you have read the pairs aloud, I want you to write down as many digits as you can remember. Any questions?

5. Read aloud these digits • 41 64 00 40 11 49 2

6. Short-term memory • The next slide contains a series of digits. The digits are presented in groups. Read groups of digits aloud. Pause between each group. For example, suppose the digits were • 248 917 142 9123 • After you have read the list aloud, I want you to write down as many digits as you can remember. Any questions?

7. Read aloud these digits • 416 400 401 1492

8. Short-term working memory • factors affecting memory span (cont’d) • recoding or chunking information; George Miller showed in his classic paper (1956) that memory span is determined by the number of ‘chunks’ or integrated items you need to recall, not the number of items presented

9. Inducing rapid forgetting • Brown-Peterson paradigm • Brown (1958) and Peterson & Peterson (1959) showed that it is possible to induce very rapid forgetting if you distract person • paradigm • study: present a small number of items followed by a number such as 632. Participant is required to count backward by threes until given a recall signal. Then he/she attempts to recall studied items

10. Inducing rapid forgetting

11. Inducing rapid forgetting • Note: Murdock (1961) showed that performance is about the same for 3 consonants as it is for 3 words, illustrating the importance of chunking • why is information forgotten in the Brown-Peterson paradigm?

12. Inducing rapid forgetting • why is information forgotten in the Brown-Peterson paradigm? • trace decay: automatic fading of memory • interference: memory is disrupted by other memory traces • proactive interference: effects of prior items on recall of subsequent items • retroactive interference: effects of subsequent items on recall of previous items

13. Inducing rapid forgetting • why is information forgotten in the Brown-Peterson paradigm? • Petersons argued that it must be trace decay; it couldn’t be retroactive interference because numbers are very different from consonants • Keppel & Underwood (1962) showed that proactive interference seemed to be responsible because if performance on the first trial only is examined there is little decline in performance over the retention interval

14. Inducing rapid forgetting • Further evidence for the importance of proactive interference (PI) • release from PI • numerous studies have established that if you present several lists of items using a Brown-Peterson procedure (Study: present list of 3 items; count backwards by 3s for 15 sec, then attempt recall of the studied items. Results show that performance declines across lists

15. Inducing rapid forgetting • Results show that performance declines across lists (build up of PI) • If you change categories, then performance increases (release from PI)

16. One or two memory systems • The theoretical question underlying much of this research had to do with whether there was evidence for the STM/LTM distinction • One approach to investigating this question involves determining whether certain tasks have separable components • One task is free recall

17. Free Recall performance (Craik, 1970)

18. Interpretation of free recall study • Primacy and intermediate components of the serial position curve are lower in the delayed compared to immediate condition; recency portion of the curve is differentially lower in the delayed condition • interpretation: delayed condition has a stronger influence on recency portion of curve because recency reflects STM performance

19. Neuropsychological Evidence for separation of STM and LTM • Data from amnesics support the viability of the distinction between STM and LTM because amnesics have normal digit span, which is mediated by STM, but are impaired in their ability to acquire and retain LTM memories

20. Neuropsychological Evidence for separation of STM and LTM • Free recall data in amnesics also supports this distinction. Given your understanding of free recall I want you to predict performance of amnesics (Baddeley & Warrington, 1970) • In immediate free recall, how should amnesics perform on the recency portion of the curve? • What about the primacy portion of the curve?

21. Short-term working memory • Atkinson-Shiffrin model of memory (1968) • distinguishes between two types of memory: short-term and long-term memory • short-term memory (STM): a temporary storage system capable of holding a small amount of information (e.g., telephone number) • information in STM is forgotten quickly unless it is rehearsed or transferred into LTM • Long-term memory (LTM): a permanent memory store with no capacity limitations

22. Atkinson-Shiffrin model of memory Rehearsal Incoming information Short-term memory Long-term memory Transfer Information displaced

23. Problems with modal model • Modal model assumes that STS plays a critical role in the transfer of information into LTS • Specifically, this model suggests that the capacity of the STS should determine the probability that an item enters LTS and • The amount of exposure in STS should affect the likelihood that an item enters into LTS

24. Problems with modal model • Both these implications are incorrect • several studies have shown that under some conditions the number of times material is rehearsed is a poor predictor that it will be recalled subsequently (shallow rehearsal)

25. Problems with modal model • Shallice and Warrington (1970) and others have established that at least some people with poor memory span (this suggests that STS is damaged) have normal long-term memory • KF memory span WAIS score = 2, Mean = 10, Standard deviation = 3 • established that KF understood spoken words by presenting a list of spoken words; task was to tap table when words were from a given category • KF also was impaired when RN STM test administered

26. Summary • Evidence supporting STM vs LTM distinction • tasks such as free recall seem to have both STM and LTM components • Neuropsychological evidence suggests that both components can be selectively damaged • amnesics have damaged LTM component, but intact STM component • KF (and others) have damaged STM but intact LTM

27. Summary • However, the modal model (Atkinson-Shiffrin) does have problems accounting for • the finding that patients with STM deficits appear to have intact LTM • maintaining an item in STM does not ensure its transfer to LTM

28. Working memory model of Baddeley • Baddeley’s early work focused on testing the hypothesis that STS is important because it acts as a working memory, a system that is important for holding and manipulating information, and it is needed for a broad range of cognitive tasks

29. Working memory model of Baddeley • Experimental paradigm (dual task paradigm) • primary task: grammatical reasoning • Determine whether sentences are true/false • e.g., A follows B -- BA (true) • e.g., B is not preceded by A - AB (false) • secondary task: concurrent digit task: remember number sequences ranging in length from 0 to 8

30. Baddeley (1986) cont’d • Results • as shown in the accompanying figure, reasoning time increased with concurrent digit load. However, performance remained high, and errors remained low (about 4% and did not vary with digit load) • thus, overall performance remains quite good, even when the overall digit load is 8 (memory span capacity)

31. Baddeley (1986)

32. Other important results • Baddeley, Lewis, Eldridge, & Thomson (1984) showed that: • a concurrent digit span task had a strong effect on encoding and remembering new material • however, it had no effect on accuracy of performance when the concurrent digit span task was performed during retrieval (although retrieval latency was slowed) • this suggests that the system responsible for holding digits does not play a critical role in retrieval as suggested by previous models of memory

33. Conclusions • These findings and others are difficult to reconcile with a model in which overloading the short-term store leads to a complete breakdown of performance on the primary task

34. Working memory model of Baddeley • Baddeley proposed to account for these results by postulating that the digit span limitations are set by one system, leaving other components of working memory relatively unimpaired • Basic model of working memory consists of a controlling attentional system (called the central executive) and two slave systems, an articulatory or phonological loop system and a visuo-spatial sketch pad

35. Baddeley’s working memory model Visuo-spatial sketchpad Phonological loop Central Executive

36. Working memory • Phonological loop characteristics • consists of a phonological store (codes speech-based information), and maintains information for about 2 seconds • articulatory control process that refreshes items in store by means of subvocal rehearsal

37. Working memory • Phonological loop • appears to play an important role in reading • poor readers tend to have poor short-term memory span • also appears to play a role in the comprehension of language and in the acquisition of vocabulary

38. Visuo-spatial sketchpad • Information can enter the sketchpad visually or through the generation of a visual image • access to this store by visual information is obligatory • the information in this store may be visual or spatial or both

39. Central Executive • The central executive plays an important role in controlling attention. Our discussion of the central executive will begin with a discussion of the interplay of attention and memory

40. Central Executive • Vigilance • recall vigilance refers to sustained attention • Parasuraman (1979) showed that vigilance performance decreases if the vigilance task has a short-term memory component involving storage and manipulation of information. For example, if the participant has to detect three consecutive odd numbers from a stream of digits or must judge whether adjacent items are of the same hue, performance declines

41. Central Executive • Vigilance • however, if the participant must evaluate each item on its own (e.g., detect whether a product such as a frying pan) has flaws, then performance tends to remain stable • Dual task performance • as discussed in a prior lecture, it is difficult to perform two tasks at the same time. However, the degree of difficulty depends upon the tasks being performed and the expertise of the person

42. Episodic buffer of working memory (Baddeley’s new model) • Overview • recently Baddeley updated the 3-component model of working memory • It proposes a 4th component, an episodic buffer • It has limited capacity • Stores information in a multimodal code • Binds information from subsidiary perceptual systems and LTM into episodic memory • Information is consciously retrieved

43. Episodic buffer of working memory (Baddeley’s new model) • Background • 3 component model of working memory consists of central executive and two slave systems, the phonological loop and the visuo-spatial sketchpad • Central executive is an attention controller • Phonological loop stores speech-based info • Visuospatial sketchpad stores visual info

44. Episodic buffer of working memory (Baddeley’s new model) • Problems with 3-component model of WM • Articulatory suppression • Saying ‘the’ repetitively (occupying the phonological loop) does not have a devastating effect on recall of visually presented numbers • Recall drops from 7 to 5 digits • One might expect recall to drop dramatically because Phonological loop is occupied and VSS is not very good at storing this type of information

45. Episodic buffer of working memory (Baddeley’s new model) • Problems with 3-component model of WM • Prose recall of a patient (PV) with word-span of 1 word is 5 words. This is less than the span of 15 words, but much more than 1 words • Possible accounts • 1. Sentences are stored in PV’s LTM. Implausible because PV has normal LTM. Also amnesic px have normal memory span

46. Episodic buffer of working memory • Possible accounts • 4. information is stored in an episodic memory buffer separate from LTM • Accounts for this result • Also accounts for finding that amnesics can retain relatively large amounts of complex information briefly (e.g., sentence span, info about a bridge game) • People integrate information across modalities (note: may be two types of integration; automatic and controlled; episodic integration is controlled integration); see binding problem discussion

47. Episodic buffer of working memory • Binding problem • Information that is processed independently by separate cognitive processes must be bound together because our experience of the world (and our memory of it as well) is coherent • People can also retrieve information about an episode when give part of an episode (e.g., given a spatial cue, state what object was stored there) • Episodic buffer is one way in which the binding problem can be solved

48. 4-component model of WM (see Fig.1) Central Exec visspat Episodic Buff Phon. Episodic LTM

49. Properties of Model • See previous notes for description of • Central Executive Function • Phonological Loop • Visual spatial sketchpad

50. Properties of Model • Episodic buffer • Integrates information across modalities and from different sources • Integrates information across time • Has limited capacity • Is capable of manipulating information • Is consciously accessible from Central Executive