Research on short-term memory developed a wide range of new approaches based on previous concepts of information processing during the 1950s, including new techniques and theoretical approaches. The multi-store model developed by Atkinson and Shiffrin (1968) has generated tremendous amounts of research. It turned out, however, that the outcome of their research had several problems with their conceptions of the characteristics of short-term memory. There has been an attempt by psychologists to determine whether there is a connection between short-term memory and working memory, so working memory is usually regarded as a component of long-term memory, which also encompasses short-term memory. The working memory according to this perspective only contain a part of long-time memory that have been recently stimulated and move them into and out of short-term memory storage.
Specifically, Baddeley and Hitch (1974) postulated that working memory represent a significant part in supporting broad range of cognitive activities related to everyday living, such as reasoning skills and language comprehension, long-term learning, and mental arithmetic. The work of Baddeley and Hitch (1974) was concerned with whether or not short-term memory could function as a working memory, this was achieved by asking the participants to perform reasoning, comprehension, and learning tasks, while they simultaneously hold 0 and 8 digits in their short-term memory for instant recall. If short-term memory serves as a working memory, then overloading it should interfere with cognitive processing, it does lead to disruption and impacted performance, but not to a great extent. Alan Baddeley and his colleagues have been actively involved in developing the idea that short-term storage is composed of many subsystems, in which around 1974 they advocated that the concept of short-term memory should be replaced with that of working memory. A central executive component, a phonological loop, and a spatial sketch pad are the three components of their model they proposed. Based on the model, working memory consists of a central executive that controls two complementary modules through limited attention, which is a modality-free component with limited capacity, and limited attention is used to control the other two modules.
Bunge et al. (2000) presented evidence for the central executive, where researchers studied the brain activity in participants while they were performing two tasks at once, reading a sentence and recalling the final word in the sentence. They used FMRI (functional magnetic resonance imaging) to see which areas were most active. An increased amount of activation was observed in the dual task condition, indicating that attention increases brain activity that affects the central executive function. Baddeley et al. (1975) also provided evidence of a visual sketchpad, where he asked participants to visualize a matrix of numbers in a task given to them at the end. There was a significant impairment in visual perception when this task was combined with the tracking of a moving light.
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An illustration of the phonological loop can be found in Baddeley et al. (1988) with the study of a patient with phonological short-term memory impairment who had difficulty learning to link new words to their meaning while learning how to link pairs of words in her native language. However, the previous models of working memory failed to explain, for instance, how information could be combined from different subsystems whose codes are different, and how it could communicate with long-term memory.
After 26 years later, Baddeley decided to introduce a 4th component called the episodic buffer. The role of the episodic buffer is to bring together information gathered from other components of working memory, as well as information about time and order, since there is no place to store information which is visual and acoustic, moreover information from the central executive, the visuospatial sketchpad, and the phonological loop is integrated into the episodic buffer. There is a belief that the episodic buffer will be a solution to some of the problems associated with the previous working memory model, including articulatory suppression, recalling of prose, and problem of binding. Introducing this component was motivated by the observation that some individuals with amnesia seem incapable of encoding new information into long-term memory, but could recall events in short-term memory much better than could be handled by phonological loops. The episodic buffer provides a solution to issues like articulatory suppression and recall of prose working memory, that have some characteristics manage by the central executive through conscious awareness, and it integrates information from multiple sources into a complex structure or episode, which has limited capacity and temporary storage. In their research on articulatory suppression, Baddeley and his colleagues (1984) asked peoples to repeat the word 'the' as they learned a visually presented list of numbers. This study predicted that no recall would take place. In making this prediction, its assumed that visual information can indirectly have access to phonological loop, whereas articulatory suppression should obstruct visual information from entering phonological loop. Moreover, a small reduction in recall was observed, typically from seven to five digits, however, this was when data from articulatory suppression was analyzed. This prove that even if there is an interference originating from the central executive, binding does not still stop, but a reduction of performance is likely to happen. A further study of injured brain patients revealed that people who have short-term memory impaired had a good recall ability at visually presented digits more than when presented digits in auditory. This indicate that a backup store for temporary information is evident here, as explained by the episodic buffer.
In conclusion to this, the episodic buffer greatly enhances the working memory model, especially also make the model better able in predicting behavior in various situations, for example, individual with amnesia. Research in psychology labs and neurophysiological studies have supported the model, for example, brain scans showing demonstrating changes in brain activity as a result of various tasks that are performed. However, it seems like that the original model was unfinished due to the episodic buffer being inserted 26 years after the original model was published, which might have limited its usefulness in explaining of working memory better. The model doesn’t incorporate all senses, which means it only consider sight and sound, and majority of the tests result supporting the model often uses artificial tasks which lack validity because the task doesn’t accurately reflect real-life scenario. Psychologists such as Cowan (2001) challenged the working memory hypothesis by proposing a model for the interaction between the central executive and the episodic buffer, while in real life situations, such as patients with amnesia and Alzheimer's disease, Baddeley's working memory model can be applied. Lastly, despite of it many critics, the model has proven a useful framework for learning, and add to our incremental growth about important cognitive functions.
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