Short-Term Memory (STM) is the second stage in today’s most widely accepted theory on memory. STM retains any information that was given attention to when it was initially stored in Sensory Memory (SM), the first stage. Information must pass through STM before it can be stored at the third stage of memory, Long-Term Memory (LTM).
STM’s function is to not only store information from SM, but to also keep it active so that it may be recalled easily. While this allows the brain to recall information quickly, the amount of information that can be stored is limited to around 5 to 7 chunks of information according to Miller (1956). This space is used up more quickly if the brain if performing multiple tasks or a singular intense task.
In comparison, Working Memory (WM) is the fundamental component of STM. While WM is usually used to refer to STM and vice versa, both are different and important terms when learning about memory.
SM is the first stage of memory, followed by STM and then LTM. It acts as a buffer for the brain as it retains information from the five senses. This information is kept for less than a second but it is retained accurately. This quick and accurate nature leads many to believe that SM is only a process for perception, however it is an essential part of memory and necessary for information to reach STM.
The five senses each create their own information in SM. Memory created through perception is known as iconic memory. An example of iconic memory is when you experience a thunderstorm in a dark room. When lightning strikes and lightens up the room, you retain a memory of what you saw during the flash though it was only visible for a second. Other types of SM are echoic memory for auditory stimuli and haptic memory for touch.
When information is first gathered through the five senses, it can be either ignored or perceived. If ignored, the memory decays almost instantly and is completely forgotten. However, if information is perceived it is then moved to SM. The act of choosing what is ignored and what is perceived is considered to be an unconscious act and unable to be manipulated consciously. Any information then given attention to during SM is moved to STM.
In response to Atkinson and Shiffrin’s (1968) multi-store model of memory, Baddeley and Hitch developed an alternative to STM: working memory. This model was composed of 3 components: the two ‘slave systems’ (the phonological loop and the visuo-spatial sketchpad) and the central executive. Often called the ‘search engine’ of the brain, WM is characterized by four crucial components. It operates over a matter of seconds, it is temporary storage, it manipulates information, and it focuses attention.
The first of the two ‘slave systems’ in WM is the phonological loop. This system retains verbal and acoustic information and continually refreshes it until it is no longer needed and deleted. The phonological loop is made up of two main components, the short term phonological store and the articulatory rehearsal. The short term phonological store retains the information while the articulatory rehearsal refreshes the sound’s representations.
There is evidence that the phonological loop exists. The retrieval of words that sound similar takes longer than the retrieval of words that sound different. Also, words that share semantic features have a weak effect on recall. According to Baddeley, Thomson, and Buchanan (1975), “Memory is impaired when people are asked to say something irrelevant aloud. This is assumed to block the articulatory rehearsal process, thereby leaving memory traces in the phonological loop to decay.”
Visual Spatial Sketchpad
The visuo-spatial sketchpad is the component of WM that holds visual and spatial information the same way the phonological loop retains verbal and acoustic information. Logie (1995) showed that similar to the process of the phonological loop, the visuo-spatial sketchpad is also subdivided into two parts. The first is the visual cache which stores information dealing with form and color. The second is the inner scribe that stores spatial and movement information as well as rehearses information in the visual cache.
Evidence suggests that there is a distinction between visual and spatial information in the brain. This is seen when brain damage causes an effect on one while the other is not affected. Specifically, the visual cache occurs in the occipital and visual cortex while spatial rehearsal takes place in the parietal lobe.
This component is a coordinating system which uses representations stored in both ‘slave systems’ to control and regulate complex cognitive tasks (i.e. perception, comprehension, and reasoning). It does this by acting as a supervisor which controls the flow of information to and from the ‘slave systems’. The central executive takes information from various sources and stores them as coherent episodes, deals with higher level cognitive functions, coordinates and shifts between multiple cognitive processes, and coordinates retrieval through selective attention and inhibition. This part of WM is found in the frontal cortex.
Adding to the theory of WM, Baddeley introduced the Episodic Buffer in 2000. The Episodic Buffer is the fourth component of WM and is the third ‘slave system’ along with the phonological loop and the visual spatial sketchpad. This component is theorized to integrate the information from the other two ‘slave systems’ and then hold all of the information on a fairly short term basis. It may also be the storage component for information that is not covered by the ‘slave systems’ (i.e. semantic, musical, and other types of information). The episodic buffer also combines all of the information into a single episodic representation that is thought to be linked to LTM and semantic information. It is not clear as to which areas of the brain are associated with the episodic buffer.
Donavon Thomas (2016), Olivia Bianchini (2017)