Working memory is more of a theoretical concept representing the theoretical framework that explains our cognitive functions – the limited capacity for the temporary storage and manipulation of information for a wide range of cognitive tasks -comprehension, reasoning, learning – beyond the simple retention and recall of information . The term working memory has been used interchangeably with short-term memory historically. The presentation of the framework of how working memory functions has to begin with the comparison of the subtle difference in the terminology of “working memory” and “short-term term”. Generally speaking, short -term memory refers to the passive storage of bits of information (or items) temporarily, in this sense, short-term memory is only the storage component of working memory that does not involve information manipulation or consolidation. Memory encoding and consolidation are not passive processes of temporarily holding bits of items in the brain (see post “memory process”). The capacity the short-term (working) memory – the number of items that can be temporarily held is about 7+/-2. Working memory emphasize the executive control function of the information manipulation process for cognitive tasks which is an active process with integration of the effect of attention.
The development of the concept of working memory is closely linked with lines of researches that lead to the proposals of several working memory models which form the theoretical framework in this area. Among them, the multi-component model perhaps is the most cited accepted working memory model that dominate the explanation of how working memory works. The model functionally divided the working memory into a “central executive controller” and temporary storage (or called “buffer”). The temporary storage was further divided functionally into three different types of storage buffer:
- visuo-spatial sketch-pad to store visuo-spatial representations;
- phonological loop to temporary store speech or language related auditory-verbal or acoustic-verbal information;
- episodic buffer is the temporary storage for episodic memory items (autobiographical facts and events)
These functional components (the 4-component model) interact with each other; and interact with their corresponding long term memory (LTM), forming a system to explain cognitive memory processes. (see figure). Despite very different theoretical methods and models adopted by researchers, there is general consensus or agreement among neuropsychologists and neurobiologists on the existence of a functional area known as “central executive controller” with limited attentional capacity. The parts of the brain believed to be involved in working memory function include (pre)frontal lobe (cortex), parietal lobe (cortex), anterior cingulate, and parts of basal ganglia.
The central executive controller is located in the frontal lobe of the brain. It is an attentional control system for the control and regulation of cognitive functions. Central executive controller manipulate information in short-term memory storage as well as information retrieved form long-term memory. The executive control component of the working memory comprises an integrated network of processes including:
- the capacity to focus attention
- to divide attention among two or more tasks simultaneously
- binding information from multiple sources into a single episodic experience
- coordinate the interaction between visuo-spatial sketch-pad, phonological loop and episodic buffer
- the ability to filter out irrelevant information (the selective inhibition functionality)
- and control access to long-term memory.
The executive functioning of the working memory has been studied extensively for patients who suffered from dysexecutvie syndrome – a deficit in working memory capacity due to the damage in the frontal lobe of the brain. Patients with dysexecutive syndrome have problems or impairments in the ability to control or focus attention, maintain goal-directed information retention against distraction. Sometimes, the patient exhibit symptoms of confabulation resulting from inappropriate association of past memory with new information. The inability to associate recalled long-term memory with new incoming information could sometimes lead to totally false memories. ADHD (The attention-deficit/hyperactivity disorder) is the medical condition associated with the problem in working memory where a set of attention and executive functioning are impaired.
The component “phonological loop”is assumed to have two basic subcomponents -a temporary speech-related/acoustic store and a subvocal articulatory rehearsal process. The speech-auditory store hold sound memory traces (when one reads the words) which are subject to rapid time decay and is a passive storage unit. The articulatory rehearsal component (or articulatory loop) is used to recall the sound memory trace via rehearsal (when one reads the words repetitively to prevent the decay). Visually presented verbal information is transformed into auditory (phonological) code by reading the word to oneself (silent articulation).
The visuospatial sketchpad is where information what we see was stored. Spatial and visual information are temporarily stored in the sketch pad where they can be manipulated by the central executive controller such as combining the shape and color of the objects, the location and speed of a moving object in space. The visuospatial component of the working memory can be divided into separate visual, spatial and possibly kinesthetic (moving) subcomponents. This conclusion was derived from the fact that brain-damage patients who showed one deficit but not the other .
The episodic buffer is where information across different domains of storage (visual-spatial, verbal-auditory, and LTM) can be collated and combined. Integrated units of visual, spatial and verbal information with chronological sequences are stored. Semantic meaning of the information is also assumed to be linked to the episodic buffer.
The framework of working memory has been implicated in the development of rehearsal strategies. Age is a factor that influence the working memory capacity. It is believed that this cognitive functional part of the brain – the working memory is most sensitive to the aging process. Aging people tend to have slower processing, manipulation and integration ability of the central executive controller. This would lead to more time-dependent decay of the information and less efficient for transferring short-term memory to long-term memory. Not only the speed declines, the capacity of the working memory also declines – less items can be held in the temporary storage for integration. Attentional control system are less efficient. Another theory of the age-dependent working memory decline is the capacity to filter out irrelevant information in inhibition function, making the memory being cluttered with interfering irrelevant information. The multi-tasking function also tend to decrease with age, making the task completing capacity vulnerable to environmental disruptions or distractions.
