Alan Baddeley and Graham Hitch presented the Baddeley model of working memory in 1974 in an attempt to give a more accurate model of primary memory (also known as short-term memory). Working memory divides main memory into several components rather than viewing it as a unitary construct.
As an alternative to the short-term store in Atkinson and Shiffrin’s’ multi-store’ memory model (1968), Baddeley and Hitch developed their three-part working memory model. Baddeley and others later expanded on this model to include a fourth element, and it is currently the accepted theory in the field of working memory. However, new models are emerging that offer a distinct perspective on the working memory system.
The model’s strength is its ability to incorporate a wide number of findings from research on short-term and working memory. Furthermore, the slave system mechanisms, particularly the phonological loop, have stimulated a variety of research in experimental psychology, neuropsychology, and cognitive neuroscience.
Baddeley Memory Model Components
The original model of Baddeley & Hitch was composed of three main components: the central executive which acts as a supervisory system and controls the flow of information from and to its slave systems: the phonological loop and the visuo-spatial sketchpad. The phonological loop stores verbal content, whereas the visuo-spatial sketchpad caters to visuo-spatial data. Both the slave systems only function as short-term storage centers.
To supplement the central executive system, a fourth component of Baddeley’s concept was introduced 25 years later. It was labeled an episodic buffer. It is a limited-capacity system that provides temporary information storage by combining data from subsidiary systems and long-term memory into a single episodic representation.
Central Executive
The central executive is a versatile system in charge of controlling and regulating cognitive processes. It directs attention and targets information, allowing working memory and long-term memory to collaborate. It can be regarded as a supervisory mechanism that governs cognitive processes, ensuring that the short-term store remains active, intervening when they go astray, and preventing distractions.
It’s functions include:
- updating and coding incoming information and replacing old information
- binding information from a number of sources into coherent episodes
- coordination of the slave systems
- inhibition, suppressing dominant or automatic responses
- selective attention
- shifting between tasks or retrieval strategies
The central executive has two major systems: the visuo-spatial sketchpad, which stores visual information, and the phonological loop, which stores verbal information.
Using the dual-task paradigm, Baddeley and Erses found, for example, that patients with Alzheimer’s dementia are impaired when performing multiple tasks concurrently, even when the difficulty of the individual tasks is adapted to their abilities.
Two tasks include a memory tasks and a tracking task. Individual actions are completed well, but as the Alzheimer’s becomes more prominent in a patient, performing two or more actions becomes more and more difficult. This research has shown the deteriorating of the central executive in individuals with Alzheimer’s.
Recent research on executive functions reveals that the ‘central’ executive is not as important as the Baddeley and Hitch model suggests. Rather, it appears that there are distinct executive functions that can vary greatly between individuals and can be selectively affected or spared by brain loss.
Phonological Loop
The phonological loop (or articulatory loop) is concerned with sound or phonological information. It is divided into two parts: a short-term phonological store containing auditory memory traces that decay quickly and an articulatory rehearsal component (also known as the articulatory loop) that can revive the memory traces.
Any auditory verbal information is believed to enter the phonological store automatically. Silent articulation can convert visually presented language into phonological code, which can then be encoded in the phonological store. The articulatory control process aids in this change.
The phonological store acts as an “inner ear”, remembering speech sounds in their temporal order, whilst the articulatory process acts as an “inner voice” and repeats the series of words (or other speech elements) on a loop to prevent them from decaying.
The phonological loop may be important in vocabulary acquisition, especially in early childhood. It may also be important when learning a second language.
The phonological loop is supported by five key findings.
- The effect of phonological similarity: Lists of words that sound similar are more difficult to remember than words that sound different. Semantic similarity (similarity of meaning) has comparatively little effect, supporting the assumption that verbal information is coded largely phonologically in working memory.
- The effect of articulatory suppression: Memory for verbal material is impaired when people are asked to say something irrelevant aloud. This is assumed to block the articulatory rehearsal process, leading memory traces in the phonological loop to decay.
- Transfer of information between codes: With visually presented items, adults usually name and sub-vocally rehearse them, so the information is transferred from a visual to an auditory encoding. Articulatory suppression prevents this transfer, and in that case the above-mentioned effect of phonological similarity is erased for visually presented items.
- Neuropsychological evidence: A defective phonological store explains the behavior of patients with a specific deficit in phonological short-term memory. Aphasic patients with developmental verbal dyspraxia are unable to set up the speech motor codes necessary for articulation, caused by a deficiency of the articulatory rehearsal process.
- On the other hand, patients with dysarthria, whose speech problems are secondary, show a normal capacity for rehearsal. This suggests that it is the subvocal rehearsing that is crucial.
Visuo-spatial Sketchpad
The visuo-spatial sketchpad is a repository for visual data manipulation. The visuo-spatial sketchpad is assumed to be its own working memory storage because it does not appear to interfere with the phonological loop’s short-term activities.
Research has found that the visuospatial sketchpad can work simultaneously with the phonological loop to process both auditory and visual stimuli without either of the processes affecting the efficacy of the other.
To explain this occurrence, Baddeley redefined short-term memory theory as working memory. According to the original theory of short-term memory, a person only has one store of immediate information processing that can only keep a total of 7 items plus or minus two things to be stored in a very short amount of time, often a matter of seconds.
The digit-span test is a perfect example of a measurement for classically defined short-term memory. Essentially, if one is not able to encode the 7 plus or minus two items within a few minutes by finding an existing association for the information to be transferred into long-term memory, then the information is lost and never encoded.
However, visuo-spatial short-term memory can retain visual and/or spatial information for short periods of time. When this memory is used, individuals can develop and revisit a mental image that can be altered in complex or challenging spatial orientation tasks.
There can also be a misunderstanding here in the differences between transient memories, such as the visual sensory memory. A transient memory is merely a fleeting type of sensory memory; therefore, as the visual sensory memory is a type of sensory memory, there is a store for the information, but the store lasts for only a second or so.
A common characteristic of visual sensory memory is that people remember seeing things that weren’t really there or forgetting specific items that were in their field of sight. The memory is fleeting, and if it is not addressed within seconds, it is lost.
Episodic Buffer
Baddeley expanded the model with a fourth component, the episodic buffer, in 2000. This part of the brain is a passive system that can only do a few things. Its job is to combine information from different areas to make units of visual, spatial, and linguistic information that are ordered in time, like remembering a story or a movie scene. It is also considered that the episodic buffer is linked to long-term memory and semantic meaning.
This component was added primarily due to the observation that some amnesia patients, especially those with high IQs, had good short-term recall of stories, recalling far more information than could be stored in the phonological loop, despite their likely incapacity to encode new information in long-term memory.
“It acts as a buffer store, not only between the components of Working Memory, but also linking Working Memory to perception and Long-Term Memory”.
Baddeley assumes that
“retrieval from the buffer occurred through conscious awareness”.
The episodic buffer enables people to envisage new concepts by using integrated units of information that they already have. Given that this could be
“an attention-demanding process…the buffer would depend heavily on the Central Executive”
The buffer may be used to gain conscious access to the phonological loop or sketchpad. This rests on the premise that the visuo-spatial sketchpad and phonological loop both function as small buffers, integrating information within their sensory domains. The episodic buffer may interact with smell and taste as well.
Biological Basis
There is a great deal of evidence suggesting a short-term memory buffer, as opposed to a long-term store. The phonological loop appears to be linked to left hemisphere activation, specifically the temporal lobe.
The visuo-spatial sketchpad activates different areas depending on task difficulty; less intense tasks seem to activate in the occipital lobe, whereas more complex tasks appear in the parietal lobe. The central executive is still a mystery, although it would seem to be more or less located in the frontal lobes of the brain.
The episodic buffer appears to be present in both hemispheres (bilateral), with activations in both the frontal and temporal lobes, as well as the left hippocampus. The gene ROBO1 has been linked to phonological buffer integrity or duration in genetic studies.
References:
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- Baddeley A, Gathercole S, Papagno C (January 1998). The phonological loop as a language learning device. Psychol Rev. 105 (1): 158–73. doi:10.1037/0033-295X.105.1.158
- Baddeley, Alan (1 November 2000). The episodic buffer: a new component of working memory? Trends in Cognitive Sciences. 4 (11): 417–423. doi:10.1016/S1364-6613(00)01538-2
- Baddeley, Alan; Eysenck, Michael W.; Anderson, Michael C. (2009). Memory. New York, NY: Psychology Press. ISBN 978-1-84872-000-8
- Baddeley, A. (2010). Working memory. Current Biology, 20(4), R136-R140
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- Murray, D.J. (1968). Articulation and acoustic confusability in short term memory. Journal of Experimental Psychology. 78 (4, Pt.1): 679–684. doi:10.1037/h0026641
- Waters, G.F.; et al. (1992). The role of high-level speech planning in rehearsal: Evidence from patients with apraxia of speech. Journal of Memory and Language. 31: 54–73. doi:10.1016/0749-596X(92)90005-I
Image: Baddeley and Hitch’s Working Memory Model. Credit: Cheese360 CC-BY
Last Updated on January 6, 2024