Working Memory II Working memory, executive control, and prefrontal cortex Cognitive Science, 9.012...

Working Memory IIWorking memory, executive control,

and prefrontal cortex

Cognitive Science, 9.012

Nuo Li

4/27/06

What is working memory?

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?

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)

Atkinson & Shiffrin (1971)

• Parallel processing of inputs• Information are selected for entry into STM• STM = Working Memory = Control processes

– Selection– Rehearsal– Coding– Decision making

Baddeley & Hitch (1974)

WM = Executive Control + Domain Specific Modules

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

Outline

• Working memory (WM) and short-term memory (STM)- WM Tasks- STM Tasks- Distinctions between WM and STM

• WM, controlled attention, and fluid integellence



• Representation

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.

Demo

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

WM tasks



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.

Demo

Is (8/4)-1=1? BearIs (6 x 2)-2 =10? DadIs (10 x 2)-6=12? Beans

Answer: Bear, Dad, Beans

WM tasks (Memory span tasks)



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

Demo

Answer: 5 8 6 3 9 9

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

STM Tasks

Wechsler Digit Span Task

Forward SpanThe examiner verbally present digits at a rate of one per second. Subject is asked to repeat the digits. The number of digits increases by one until the participant consecutively fails two trials of the same digit span length.

Backward SpanThe backward test requires the participant to repeat the digits in reverse order.

WM & STM

What’s the difference?

WM & STM

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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).

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).

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

Effect of Proactive InterferenceOthers 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: sameList 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.

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.

WM & STM

STMStorage of information.

Limitation: How many item can be stored.

WMDifferent 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

Outline





• Representation

WM is Capacity Limited

“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

Memory capacity vs.

Cognitive control capacity

Model of WM, Engle

WM = STM + controlled attention

Three components:1. a store in the form of long-term memory traces active

above threshold2. processes for achieving and maintaining that activation3. Controlled attention (capacity limited, individual

performance difference arise)

Model of WM, Engle

Central Executive(working memory capacity, controlled attentions)

a. Achieve activation through controlled retrievalb. Maintain activation (to the extent that

maintenance activities are attention demanding).c. Blocking interference through inhibition of

distraction

Strategies, procedures for maintaining activation

a. Could be phonological, visual spatial, motor, auditory, etc

b. More or less attention demanding depending on the task and subject

Activated portion of long term memory

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.

STM

LTM

Empirical Support

Two questions:

1) Is separate construct of STM and WM necessary?

2) 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?

Operation span

Reading span

counting span

backward span

forward span

Forward span w/ similar sounding word

WM

STM

COMMONGeneral fluid intelligence

Ravens standard progressive matrices test

Cattell fair test of intelligence

.77

.63

.61

.67

.79

.71

.81

.85

.49

.12

.91

.74

.29

Empirical Support

Engle et al (1999)

133 subjects performed 8 different tasks

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


Antisaccade Task

Require suppression of the natural tendency to saccade to the flashed cue.

WM span assessed on operation-span task.

cue target

Kane et al (1999)

AIdentification of target by pressing key

cue targetA

Identification of target by pressing key

Pro-saccade

Anti-saccade

WM and Fluid IntelligenceResult



Kane et al (1999)



Reflexive Eye Movement

Reaction Time

Eye movement not monitored in this case


Stroop task Dots: Words: Colours:

• LONG BLUE

• AND RED

• VERY BLUE

• BUT GREEN

• HEAVY RED

• SHORT BLUE

• NEAR GREEN

• WITH BLUE

Result


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 reported65% low WM span subject reported

Conclusion

High WM span people suppressed distractor information better

Current WM Models

Baddeley & Hitch

Central Executive


STM

LTM

? Engle

Outline




• Representation • Mapping from functions to structures

PFC Anatomy

DorsolateralInput mainly from medial, dorsolateral cortical areas. (somatosensory, visuospatial information)

LateralInputs mainly from ventrolateral and ventromedial cortical areas (auditory, visual pattern information)

Segregation of functions? More on that later…

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.


Stroop task

London tower

Other cognitive tasks:Dots: Words: Colours:

• LONG BLUE

• AND RED

• VERY BLUE

• BUT GREEN

• HEAVY RED

• SHORT BLUE

• NEAR GREEN

• WITH BLUE

All these cognitive task involves a memory component

Q: deficit in memory component vs. executive control?


Owen et al (1996)

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

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spatial

verbal

visual

Conclusion: prefrontal contribution to WM is the mediation of problem-solving strategies and not in memory per se.


Other memory tasks

Inability to suppress irrelevent information, sensitive to proactive interference

Shimamura 1995


Deficits in recalling temporal ordering, but no deficit in recognition.

Recall temporal-sequence

Milner & Petrides, 1984 Shimamura 1995

PFC Anatomy in Other Species

PFC Deficit in Nonhuman PrimatesWorking 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

PFC Deficit in Nonhuman Primates

Dias, Robbins & Roberts, 1996





Lateral PFC Lesion: Slower to learn new criteria when the diagnostic dimension is changed.

Orbital PFC Lesion: Learn new criteria normally, slower to relearn.

PFC Deficit in Nonhuman Primates

After dorsolateral PFC lesion

Error on contralateral visual fieldPerformance decay with time

Funahashi , Bruce, & Goldman-Rakic (1993)

Fixation Point

Target

Delayed saccade task

Saccade!

PFC Neural Response

Anti-saccade task

Funahashi, Chafee, & Goldman-Rakic (1993)


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Error Trials

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.

Outline





• Representation

Verbal storage





storage

storage+processing

Verbal storage

Activation in left posterior parietal cortex (Brodmann’s area)3 frontal sites (Broca’s area)Left supplementary motor and premotor area





storage

Storage+process

0- and 1-backItem recognition

2- and 3-backFree recall

Smith & Jonides, 1999 (review)

Visuospatial





visual

spatial

Visuospatial





Smith & Jonides, 1999 (review)

Spaital (blue)Object (red)

Some insights from Imaging studies

• Imaging studies show that working memory is mediated by frontal cortex and a collection of posterior regions differing in the types of information maintained.

• Posterior cortical regions seem to specialize in the type of information held in working memory

• Frontal area may have a special role in integrating different type of information

Outline





• Representation

WM Representation

Domain general vs. Domain specific?

Baddeley & Hitch

Central Executive


STM

LTM

Engle

Domain General?





Conclusion: More than half of the neuron (64/123) contain both “what” and “where” information

Rao, Rainer, & Miller (1997)



But wait…



Wilson, Scalaidhe, Goldman-Rakic 1993

Lateral PFC24/31 selective for pattern6/31 selective for both1/31 selective for spatial information

Conclusion: segregation of “what” (lateral) and “where” (dorsolateral)

Cue Delay Response

Thank you!

Backup slides

PFC Neural Response

Primate performing a delayed response task

Milner & Petrides (1984)

PFC Neurons

PFC Neural ResponseCue-delay-saccade

Funahashi , Bruce, & Goldman-Rakic (1989)

Q: memory of cue vs. motor preparation?



PFC Neural ResponseQuintana & Fuster (1992)

Dissociation of memory of cue from motor preparatory cue

PFC Neural Response

Rainer Asaad & Miller (1998)







Delayed match-to-sample task

SpatialJonides, Smith, Koeppe, Awh, Minoshima, Mintun. (1993)







Areas for spatial memory task

Domain General?


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Suchan, Linnewerth, Koster, Daum, & Schmid (2006)

Cross-modal processing

Working Memory II Working memory, executive control, and prefrontal cortex Cognitive Science, 9.012...

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