Working Memory (STM) Flashcards
what is working memory
the ability to hold, manipulate and utilise information in mind independently of sensory stimulation in order to guide behaviour
early ideas about short term memory
Ebbinghaus (1885) plotted the first forgetting curve based on empirical studies
James (1890) suggested a major division between primary (short term) and secondary (long term) memory on introspective and theoretical grounds
Hebb (1949) suggested that these two memory constructs could be supported in different ways in the brain
STM: through reverberation in cell assemblies
LTM: through synaptic plasticity
Properties of STM
limited capacity store (verbal and non-verbal material)
separable from earlier echoic/iconic memory
eveidence for limited capacity store (Miller 1956)
Review of studies indicates a limitation of STM: to seven digits.
Universal plateau at 7 - span of absolute judgement
evidence that STM is separable from earlier Iconic/Echoic Memory (Sperling, 1960; Neisser, 1967)
Stimulus arrays of letter in different formations and numbers
Test how much could be recalled
Plateau at 4
The act of reporting may interfere with actual number in STM
Introduced a post cue to report specific row - found much higher performance
Suggests initial span is much greater than what is actively recalled
Highlights a distinction between STM and ‘iconic traces’
There is an effect of cue delay: when cued after 1 sec of presentation performance plateaus again (see graph).
Crit: as recall is verbal it could be argued verbal STM is being measured (not visual)
evidence limited capacity extends to non-verbal material (Phillips & Baddely, 1971)
Task required participants to compare flashed checkerboard stimuli
The closer recall probe is to presentation, the greater performance is
Shows limited capacity properties are observed for non-verbal material
Evidence STM decayse rapidly without reheearsal (Peterson & Peterson, 1959)
Participants were asked to repeat a number that is heard among a chain of letters, count backwards in 3s until they are stopped and then recall the letters.
Performance decreases with time passed and is never at 100%
This shows that STM decays rapidly without rehearsal
BUT the numbers may overwrite the letters due to an interference effect
The similarity of items interacts strongly with forgetting (Keppel & Underwood, 1962)
The more trials individuals must complete, the worse their performance gets
This is because the content can be held as salient and distinct from other trials for only a short period of time
After this the similarity of items interacts strongly with forgetting → proactive inhibition
Studies of release from proactive interference (Wickens et al., 1963)
Showed that switching participants to new materials (from numbers to letters) after different numbers of trials results in a bounce back in performance as the interference doesn’t carry through
This supports the proactive interference account
However there is still the possibility of decay
serial order effect (Murdock, 1962)
Participants had to memories different numbers of simple words, with the aim to outspan
Time gaps between learning and recall were manipulated
Found that the quantity of items was more important than time passing
About seven words could be kept in a priority state, with the first and last presented best remembered
Primacy and Recency effects suggest LTM and STM components are involved
Contributions of both proactive and retroactive inhibition in performance
Neuropsychological evidence for double dissociation in STM and LTM
Spared STM but Impaired LTM (Milner 1966, 1970)
STM spared in amnesic patients with LTM deficits
E.g patient HM with lesioned MTL can hold a number in mind for sustained period of time (584 for 15 minutes) by continuously working out elaborate mnemonic schemes but as soon as he is distracted he cannot remember even having held a number in mind
Impaired STM and Spared LTM (Shallice & Warrington, 1970)
Patient with deficits in verbal STM and not LTM, suggestive of a double dissociation
KF had a lesioned left parietal area
When tested on serial recall, the first two items were best recalled, with a plateau in performance on all other positions bar the very last item.
Suggestive of a primacy effect but impaired recency effect which is indicative of an issue with proactive and retroactive interference
HM would show the opposite pattern and further test support a function LTM
However the tests are not really comparable and the evidence is weak
Also seems a contradiction that information can enter LTM if there is no STM
modal model (Atkinson & shiffrin, 1968)
Proposes functional distinctions among early sensory memory, STM and LTM
STM: critical interface between perceptions and LTM for guiding cognition and action
STM includes storage and control functions
Does not assume physically separate stores
Working memory model Baddeley
Working Memory Model (Baddely & Hitch, 1974)
Motivated by functional and neuropsychological dissociations, it had 3 components
Phonological Loop
Limited capacity store for speech (and acoustic) information
Subject to rapid decay and maintained through subvocal articulation
Supported by
phonological similarity effect (Conrad, 1964)
Word length effect (Baddeley, 1975)
Developmental correlation between articulation and span (Nicolson, 1981)
Visuospatial Sketchpad
Limited capacity storage for visual, spatial and maybe kinaesthetic information
Showed more limited decay
Unclear maintenance mechanism (Saccades?)
Central Executive
Underdefined
Initially proposed to contain a limited pool of general processing capacity
Then borrowed from the supervisory attention system arguing for a purely control function
Working Memory Model 2 Baddeley (2000)
Episodic buffer
Provides storage for complex material
Interface for integrating perceptual, WM subsystems and LTM into a few episodes
structure of information in WM
Slots and Resources (Zhang & Luck, 2008; Bays & Husain, 2008)
Present participants with a number of items
Ask people to produce precisely the information (colour) that was in that item
Used decision judgements to derive whether people are reporting something they can retrieve and how accurate this representation is - or if they forget.
Over 3 stimuli there is more guessing behaviour
Units/ slots
Spread resources
Nature of information in WM
(Stokes & Nobre, 2019)
Representational vs Functional
In a functional account, WM provides the informational content (from mnemonic traces extracted from experience) for guiding selection and prioritisation (i.e., attention) during perception.
