The phonological loop is then another component of the working memory, which in itself was further subdivided into the articulatory process and the phonological store. The articulatory process is used for words that are heard or seen and has capacity of about 2 seconds. These words are silently rehearsed, like an inner voice, and are a form of maintenance rehearsal. Then there’s the phonological store and this holds the words you hear. It has a very short duration of about 2 seconds, unless it is rehearsed by the articulatory control system. The phonological store receives its information either directly from the ears or from long term memory. The word-length effect is used as evidence of the phonological loop, with the fact that people cope better with short words than long words in short term memory. It seems that the phonological loop holds the amount of information that you can say in two seconds. This makes it hard to remember a list of long words compared to shorter words. The longer words can’t be rehearsed on the phonological loop because they don’t fit. However, the word-length effect disappears if a person is given an articulatory suppression task, for example if you are asked to say a repeated word while reading the words. This repetitive task ties up the articulatory process and means you can’t rehearse the shorter words more quickly than the longer ones, so the word-length effect disappears. This is evidence for the articulatory process.
Next within the working memory model is the visuo-spatial sketchpad component. Visual and/or spatial information is temporarily stored here and it is used when you have to plan a spatial task like getting for one room to another. Visual information is what things looks like, and spatial information is the relationship between things. Baddeley et al. (1975) demonstrated the existence of the visuo-spatial sketchpad. Participants were given the visual tracking task of having to track a moving light with a pointer. At the same time they were given one of two other tasks: task 1 was to describe all the angels on the letter F and task 2 was to perform a verbal task. Task 1 was very difficult but not task 2, presumably because the second task involved two different components.
The last of the four components of the working memory model is then the episodic buffer. Baddeley (2000) added the episodic buffer because he realised the model needed a general store. The phonological loop and visuo-spatial sketchpad deal with processing and temporary storage of specific kinds of information. The central executive has no storage capacity; so there was nowhere to hold information that relates to both visual and acoustic information. The episodic buffer is an extra storage system that has, in common with all working memory units, limited capacity. The episodic buffer integrates information from the central executive, the phonological loop, the visuo-spatial sketch pad and also for long-term memory. Baddeley et al (1987) found evidence for the episodic buffer in that, when participants were shown words and then asked for immediate recall, their performance was much better for sentences (related words) than for unrelated words. This supports the idea of an immediate memory store for items that are neither visual nor phonological and that draw on long-term memory (to link the related words).
Just like any research, the working memory model has strengths and weaknesses. The working memory model is valid and plausible. In this case, it seems plausible because it fits with everyday experiences like manipulating information when solving problems, with short term memory as an active process rather than a static store. For example, Baddeley (1997) suggests that mentally counting the number of windows in your house demonstrates the operations of working memory. Normally a person will imagine each room in turn, forming a mental image of each window (Visuo-spatial sketchpad), they will count using the phonological loop to rehearse the numbers and this will all be coordinated by the Central Executive. Then another strength of the working memory model is that verbal rehearsal is not necessary for all types of information; just verbal strings. For example, we do not have to rehearse everything that happens to us because events are processed by the episodic buffer
The working memory model also has weaknesses though. The most important weakness of the working memory model is that the functions of the central executive are vague and difficult to test. For example, Baddeley claims that the central executive has a limited capacity; however, how this capacity can be measured independently of the other components is unclear. Baddeley also claims that the central executive can be divided into subsystems; however they have not yet been identified and it is difficult in practice to determine which processes that control the components are part of the central executive and which are part of other systems.