Working Memory II Working memory, executive control, and prefrontal cortex

1. Working Memory IIWorking memory, executive control, and prefrontal cortex Cognitive Science, 9.012 Nuo Li 4/27/06

2. Active maintenance of goal related information in the face of distractors and interference. It’s task dependent and involves some degree of cognitive control. What is working memory?

3. What is working memory? • Some defining characteristics: • goes on in consciousness • accessible to explicit form of expression (declarative memory) • elaboration of short-term memory • selective • involves cognitive processing (e.g. recognition)

4. Atkinson & Shiffrin (1971) • Parallel processing of inputs • Information are selected for entry into STM • STM = Working Memory = Control processes • Selection • Rehearsal • Coding • Decision making

5. Baddeley & Hitch (1974) WM = Executive Control + Domain Specific Modules

6. Outline • Working memory (WM) and short-term memory (STM) • WM, controlled attention, and fluid intelligence • Role of pre-frontal cortex (PFC) • Mapping from functions to structures • Representation

7. Outline • Working memory (WM) and short-term memory (STM) • WM Tasks • STM Tasks • Distinctions between WM and STM • WM, controlled attention, and fluid integellence • Role of pre-frontal cortex (PFC) • Mapping from functions to structures • Representation

8. WM tasks Reading span (Daneman & Capenter, 1980) Subject read (or listen to) a list of 2 to 6 sentences. Afterward, the subject recalled the last word of each sentence.

9. Demo For many years, my family and friend have been working on the farm. SPOT Because the room was stuffy. Bob went outside for some fresh air. TRIAL We were 50 miles out at sea before we lost sight of the land. BAND ANSWER: SPOT, TRIAL, BAND

10. WM tasks Reading span (Daneman & Capenter, 1980) Subject read (or listen to) a list of 2 to 6 sentences. Afterward, the subject recalled the last word of each sentence. Operation span (Turner & Engle 1989) Subject solved a string of arithmetic operations and then read aloud a word that followed the string. After a series of such operation-word strings, the subject recalled the word.

11. Demo Is (8/4)-1=1? Bear Is (6 x 2)-2 =10? Dad Is (10 x 2)-6=12? Beans Answer: Bear, Dad, Beans

12. WM tasks (Memory span tasks) Reading span (Daneman & Capenter, 1980) Subject read (or listen to) a list of 2 to 6 sentences. Afterward, the subject recalled the last word of each sentence. Operation span (Turner & Engle 1989) Subject solved a string of arithmetic operations and then read aloud a word that followed the string. After a series of such operation-word strings, the subject recalled the word. Counting span (Case, Kurland, & Goldberg 1982) Subject is presented with up to eight displays. Each display consists of different number of targets, and two other kinds of distracters, all randomly placed. Subject is required to count the targets aloud, and report the final tally. After the series of displays, the subject is required to report previous final tally in order

13. Demo Answer: 5 8 6 3 9 9

14. WM tasks • These tasks are thought to reflect some fundamental aspect of cognition. Score on these tasks predict a range of cognitive functions: • Reading & listening comprehension • Following directions • Vocabulary learning • Note taking • Writing • Reasoning • Bridge playing • Computer language learning • etc

15. STM Tasks Wechsler Digit Span Task Forward Span The examiner verbally present digits ata rate of one per second. Subject is asked to repeat the digits. The numberof digits increases by one until the participant consecutivelyfails two trials of the same digit span length. Backward Span The backward test requires theparticipant to repeat the digits in reverse order.

16. What’s the difference? WM & STM

17. Brown–Peterson distractor task: Recall trigram of consonants (e.g. GKT, WCH,…) after performing a number of algebraic computations (e.g., counting backwards by 3’s). Keppel and Underwood (1962) found that forgetting in the Brown–Peterson distractor task depends on where in the experimental session performance is assessed. (On the very first trial, the recall performance was near perfect). WM & STM Goes against the classic notion of information has to be rehearsed in order to be retained. Proactive interference plays an important role in short-term retention

18. Effect of Proactive Interference Others also found similar effects: Rosen & Engle (1998) Subjects (with high and low WM score) learn to associate 12 cue word with 3 list of other 12 words. Instruction emphasized accuracy Example: list 1: bird-bath; list 2: bird-dawn; list 3: bird-bath; (re-learn) Measured both timing and accuracy. Result: List 1: same List 2: low WM made more error (showed intrusion from list 1) List 3: high WM responded slower than low WM subjects, even slower than themselves on trial 1. Conclusion: information in list1 is suppressed better for the high WM subjects, which affected their performance on later trials.

19. Effect of Proactive Interference Kane & Engle (2000) Subject (with high and low WM score) had 3 trial in which they saw 10 words to recall. The subject performed a rehearsal preventative task for 16s. Result: Trial 1: high WM and low WM subject performed the same (60%) Subsequence trials: low WM had steeper decline in recall performance Adding secondary preventative task (adding interference load) The two group performed the same. Conclusion: When add more interference load, high WM subjects were hurt more, suggest that under normal condition, high WM subjects allocate more attentional control to combat the interference.

20. WM & STM • STM • Storage of information. • Limitation: How many item can be stored. • WM • Different from passive storage, WM is active maintenance of goal related information relevent to a task in the face of proactive distractors. There is addition of mental “work” (cognitive processing) and its combination w/ “memory”. ( more than just STM), involves recognition & comprehension. • Limitation: memory component & control component

21. Outline • Working memory (WM) and short-term memory (STM) • WM, controlled attention, and fluid intelligence • Role of pre-frontal cortex (PFC) • Mapping from functions to structures • Representation

22. WM is Capacity Limited Memory capacity vs. Cognitive control capacity “Greater working memory capacity does not mean that more items can be maintained as active, but this is a result of greater ability to control attention,…ability to use attention to avoid distraction.” -Engle RW

23. Model of WM, Engle WM = STM + controlled attention • Three components: • a store in the form of long-term memory traces active above threshold • processes for achieving and maintaining that activation • Controlled attention (capacity limited, individual performance difference arise)

24. Model of WM, Engle Central Executive (working memory capacity, controlled attentions) Achieve activation through controlled retrieval Maintain activation (to the extent that maintenance activities are attention demanding). Blocking interference through inhibition of distraction Magnitude of this link is determined by the extent to which the procedures for achieving the maintaining activation are routinized or attention demanding. Thus, it is assumed that, in intelligent, well-educated adults, coding and rehearsal in a digit span task would be less attention demanding than in a 4-year old children. Strategies, procedures for maintaining activation STM Activated portion of long term memory Could be phonological, visual spatial, motor, auditory, etc More or less attention demanding depending on the task and subject LTM

25. Empirical Support Two questions: Is separate construct of STM and WM necessary? Once the common variance to WM and STM is removed, do the WM residual variance (which should reflect controlled attention) correlate with the residual for general fluid intelligence?

26. Operation span .77 .49 Reading span .63 WM Ravens standard progressive matrices test .61 .81 .91 counting span General fluid intelligence .29 COMMON backward span .85 .67 Cattell fair test of intelligence .74 .79 STM forward span .12 .71 Forward span w/ similar sounding word Empirical Support 133 subjects performed 8 different tasks Engle et al (1999)

27. WM and Fluid Intelligence • Controlled attention is closely related to general fluid intelligence • Performance task on WM task predicts performance on other cognitive tasks e.g. performance on reading span task correlates well with reading comprehension

28. WM and Fluid Intelligence Antisaccade Task Identification of target by pressing key Pro-saccade A target cue Identification of target by pressing key Anti-saccade A target cue Require suppression of the natural tendency to saccade to the flashed cue. WM span assessed on operation-span task. Kane et al (1999)

29. WM and Fluid Intelligence Result Reflexive Eye Movement Reaction Time Eye movement not monitored in this case Kane et al (1999)

30. WM and Fluid Intelligence Stroop task Result

31. WM and Fluid Intelligence Dichotic listening task Subjects repeat aloud words presented to one ear while ignoring information presented to the other ear. At some point, subject’s first name is spoken to the ignored ear. Report whether they heard their name during the trial. Result 20% high WM span subject reported 65% low WM span subject reported Conclusion High WM span people suppressed distractor information better

32. Current WM Models ? Engle Baddeley & Hitch Central Executive Strategies, procedures for maintaining activation STM LTM

33. Outline • Working memory (WM) and short-term memory (STM) • WM, controlled attention, and fluid intelligence • Role of pre-frontal cortex (PFC) • Representation • Mapping from functions to structures

34. PFC Anatomy Dorsolateral Input mainly from medial, dorsolateral cortical areas. (somatosensory, visuospatial information) Lateral Inputs mainly from ventrolateral and ventromedial cortical areas (auditory, visual pattern information) Segregation of functions? More on that later…

35. PFC Deficits in Human Wisconsin card sorting Results: No difficulty learning the rule initially. (memory component) But once learning a rule, patient could not switch.

36. PFC Deficits in Human Other cognitive tasks: Stroop task London tower All these cognitive task involves a memory component Q: deficit in memory component vs. executive control?

37. PFC Deficits in Human Owen et al (1996) spatial Task: Find the hidden squares Result: Normal controls: developed successful self-ordered search strategy Temporal lob lesion patients: only failed on most difficult task PFC lesion: failed on most easy task verbal visual Conclusion: prefrontal contribution to WM is the mediation of problem-solving strategies and not in memory per se.

38. PFC Deficits in Human Other memory tasks Shimamura 1995 Inability to suppress irrelevent information, sensitive to proactive interference

39. PFC Deficits in Human Recall temporal-sequence Milner & Petrides, 1984 Shimamura 1995 Deficits in recalling temporal ordering, but no deficit in recognition.

40. PFC Anatomy in Other Species

41. PFC Deficit in Nonhuman Primates Working memory task Associative memory task PFC lesioned primates: Deficit in working memory task, but not in discrimination task PFC lesioned primates also show deficit in spatial-delayed alternation task

42. PFC Deficit in Nonhuman Primates Lateral PFC Lesion: Slower to learn new criteria when the diagnostic dimension is changed. Orbital PFC Lesion: Learn new criteria normally, slower to relearn. Dias, Robbins & Roberts, 1996

43. PFC Deficit in Nonhuman Primates Funahashi , Bruce, & Goldman-Rakic (1993) Delayed saccade task Fixation Point Target Saccade! After dorsolateral PFC lesion Error on contralateral visual field Performance decay with time

44. Error Trials PFC Neural Response Anti-saccade task Funahashi, Chafee, & Goldman-Rakic (1993)

45. PFC Deficits Dorsolateral - Spatial delayed response - Spatial delayed alternation task - No deficit in discrimination Lateral - Object alternation - Delayed non-match to sample Orbital - Deficits in olfactory, taste, visual and auditory discrimination - Discrimination reversal learning.

46. Outline • Working memory (WM) and short-term memory (STM) • WM, controlled attention, and fluid intelligence • Role of pre-frontal cortex (PFC) • Mapping from functions to structures • Representation

47. Verbal storage storage storage+processing

48. Verbal storage Activation in left posterior parietal cortex (Brodmann’s area) 3 frontal sites (Broca’s area) Left supplementary motor and premotor area storage 0- and 1-back Item recognition Storage+process 2- and 3-back Free recall Smith & Jonides, 1999 (review)

49. Visuospatial visual spatial

50. Visuospatial Spaital (blue) Object (red) Smith & Jonides, 1999 (review)