Cognitive Lecture 4: Cognition and Short Term Memory

Working Memory

Processes need a 'mental workspace': external and internal stimuli processing, transformation, make and act on decision, use outcomes for future decision making 

Working memory is a system allowing us to temporarily retain and manipulate info to perform activities e.g. reasoning, learning and understanding 

STM is part of working memory - the retention and basic processing of information in simple tasks 

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Patients with pure organic amnesia have difficultly creating new memories e.g. learning but can have a conversation and perform well in info. processing (tasks) 

Information is not physically present but they are able to briefly retain while they process it 

Amnesiacs forget quickly/if distracted 

This data suggests presence of a limited duration memory 

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STM Duration

Ppts given single trigram then replaced by a 3 digit sequence and asked to count backwards for a range of seconds 

Steady decline in memory of trigram as seconds increase (Peterson and Peterson) (15-30 seconds) 

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STM Verbal Span

Digit span tests: require ppts to listen to a series of digits and repeat them in order immediately after (5-9 items) - Miller, 1956

The exact number could be different depending on word length, digit span higher than for words, and for words it could depend on number of syllables or phonemes (longer word, shorter span)

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STM Visual Span

Visuospatial digit span: several techniques e.g. corsi block tests (taps sequence on the board at a steady pace of 1 per second) repeated in same order by ppts, number of taps increases gradually

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STM Capacity

STM uses chunking, chunks represent groupings of individual events, making use of existing knowledge and preferences to understand and organize material e.g. personal semantics (2,4,1,2, or 24th December), prosodic references (easier to remember phone numbers in 3s), phonological plausability (meaningless words we can remember those we phonetically pronounce better), expertise (people who see foreign words = one chunk)

SF: could recall 90 digits 

Cowan, 2010: range of 3-5 chunks with verbal materials in various tasks 

Miller (1956): people may rehearse covertly in tasks - when this is prevented capacity may be reduced 

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Sequential comparison task

STM: accuracy scores for different array sizes show a drop off when array size exceeds 4 items, similar drop in accuracy when other features are tested (orientation, colour, shape), and when memory is tested for conjunction = visuospatial capacity is around 4, items are stored as integrated objects, binding (Luck and Vogel, 1997) 

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Atkinson and Shiffrin (1968/71): 3 memory stores - sensory, STM, LTM

Sensory and short term retain info for short periods and LTM is potentially permanent, STM limited, LTM vast, serial model where info is transferred through stores, input to STM comes from environment and LTM, to retain info needs to be rehearsed

Neuropsych evidence: Warrington and Shallice (1989) - KF showed impaired STM but not LTM - not serially connected, also showed deficits of verbal STM but not in visuospatial tests, other patients show reverse impairment, STM comprises more than one store (modality) 

STM not single unitary system, prob of creating LTM depends on type of memory not rehearsal, no serial transfer of information across stores (STM not a prerequisite for LTM), emphasizes storage not more complex cog e.g. decision making, reasoning, lang comprehension

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Multicomponent model of working memory: Phonologic

Baddeley and Hitch (1974): contains specific systems (phono. loop and visuospatial sketchpad), central control comes from exec, episodic buffer binds distinctive features 

Phono loop: verbal STM, auditory and visual inputs, CODING: auditory similarity affected performance in word repetition task than semantic similarity, CAPACITY: inc. word length decreases items we can hold, longer words take longer to read, rehearse etc. we remember this as this is what we can rehearse (7 words - Baddeley, Thomson and Buchenen, 1975), PROCESSING: articulatory suppression disabled the articulatory control process, written words not converted into phonological code and rehearsed so fewer recalled (spoken have direct access to phono. store) - deficits affect foreign lang. learning (PV) doesnt affect learning of native pairs of words, Service, 1992: phono. capacity predicted eng. learning in finnish schools, lang impaired children performed worse in a non-word repetition task affect inc. with phono. load. 

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WM: evidence for separate stores

Quinn and McConnel (1996): ppts presented with series of words, in 1 they rehearsed while experiencing verbal, visual or no interference, 2) create a mental image with interference

Irrelevant speech affected memory under mnemonic instruction but not visual, visual noise disrupted visual condition but not verbal, this pattern = two stores 

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Multicomponent model of working memory: VSSP

Logie (1995): visual and spatial information depend on different stores within the VSSP - visual cache (shapes, patterns, colours), inner scribe (spatial information, location, movement, content of VC rehearsal) 

Klauer and Zhao (2004): visual memory task (VC), and dot location (IS) - if VSSP was single store, interference would impact both tasks 

Inner Scribe manipulation: ppts given 15 shapes and names, given 5 (2 mins) to create a pattern, secondary task of tapping sequence, under supression condition (tapping) ppts created fewer patterns but remembered same individual parts, articulatory suppression instead of tapping: affected both pattern creation and memory of parts 

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Multicomponent model of working memory: episodic b

Needed to interact with LTM, essential for chunking, incoming info = events so storage required for these individual forms 

Capacity = 4 chunks 

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Multicomponent model of working memory: central ex

attentional control system: 1) automatic/SA control system - decision making, conflict resolution in complex/habitual situations, 2) supervisory attentional - decision making and conflict resolution in novel situations, receives input from subsystems, selects info, overrides responses 

- Retains attentional focus, selective attention, dividing attention, inhibition control 

- Dual task performance, random generation, switching between rules and inhibition of previous responses 

- Dysexecutive syndrome: damage to frontal lobes e.g. Alzheimer's 

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State theories

Cowan: embedded processes model - working memory doesn't consist of separate temporary stores but is within LTM, involves CE (flashlight attention), attentional focus triggered by internal and external events, diff features in diff states attention can focus on all in turn 

Hybrid model: combines structural and functional elements, retains CE, introduces activated features, states which become a centre of attention 

WM is an emergent property of focusing attention to activated features 

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Mediating STM/WM

Deficits in verbal short term: which parts are important for verbal STM, patients EE and KF show specific impairment in digit span but normal LTM and lang. functions, both damaged left angular gyrus; Left inferior: stores phonological codes; Activity in this area + Broca's = articulation and articulatory control processes 

Imaging spatial working memory: neuroimaging data, fixation vs WM tasks asking to match test pattern to sample, activity differences in bilateral frontal parietal regions but greater correlations of activity between right frontal and parietal regions (Pessoa, 2002)

Visuo-spatial deficits: object and spatial STM dissociated in the brain, patients can show impaird object STM but intact spatial, patient MV - damage to right frontal and parietal lobes following a stroke had impaired STM on corsi test but not visual STM task

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