Key Differences Between Short-term Memory and Long-term Memory

Memory is ‘the ability to retain information or representation of past experience, based on the mental processes of learning or encoding, retention across some interval of time, and retrieval or reactivation of memory’ (APA Dictionary). To the innocent eye, memory can be viewed as a simple concept from which we recall information; however, overtime, as psychologists have investigated and divulged memory, they have discovered just how complex our memory is. In this essay, I explore memory in terms of the two major memory stores of the short-term and long-term memory through psychological theories and experimental evidence.

Short-term memory was found to have a limited capacity by Miller (1956) who revealed that this store’s memory span can account for seven plus or minus two piece of information at a time. Miller also disclosed the concept of ‘chunking’ for which is ‘a process of organizing or grouping the input into familiar units or chunks’ (Miller, 1956:93); this processing allows for more information to be encoded. For example, the Royal Bank of Scotland is better known as RBS, as people remember the name of the bank in a shorter ‘chunk’ of information. Duration of the short-term memory is also an important factor as we can only hold information in this store for less than minute. However, with rehearsal, information can be transferred to the long-term memory, which has a much larger duration. If information is not rehearsed, it’s lost through decay. Peterson and Peterson (1959) investigated duration of the memory store through forgetting rates. From their experiments, it was found that letter recall decreased from above 90% after 3 seconds, 50% around 6 seconds to less than 10% at 18 and therefore rapid loss was seen as unrehearsed information is lost through decay.

The memory store has been adapted and viewed as being the working memory model by Baddeley and Hitch (1974). This model has 3 main components: phonological loop (processing verbal and auditory information), visuospatial sketchpad (processing visual and spatial information) and the central executive (integrated information – both types, visuo-spatial and phonological information, come together). The working-memory model is thought to have a limited capacity, just as the short-term memory was discovered to have, and therefore, both can only hold a limited amount of information temporarily. Baddeley and Hitch tested the original two systems of the phonological loop and the visuo-spatial sketchpad, that if a participant was asked to process two pieces of sound information simultaneously, they would not be able to do so. This is due to the phonological loop having a restricted capacity resulting in an inability to cope with the demands of processing two tasks at once. However, if the participant was presented with both visual and sound information concurrently, they would be able to process the information successfully due to them being different stores. In 2000, Baddeley added the fourth component to the working the memory: the episodic buffer. This is the ‘temporary storage system that can hold and integrate information from the phonological loop, the visuo-spatial sketchpad, and long-term memory’ (Eysenck & Keane, 2010: 212). The central executive information is fed in and out pathways of crystallised systems which include visual semantics, episodic long-term memory and language. Therefore, the episodic buffer restores anything learned in the long-term, but it also needs someway of holding multimodal information in order to be able to retrieve.

The long-term memory store is identified as having an infinite capacity and duration for holding information and the store is divided into declarative and non-declarative memory.  Declarative memory, also referred to as explicit memory, involves conscious recall of facts and events. Non-declarative memory, also known as implicit memory, is our skills and procedure of events that we obtain through changes in our behaviour. Developing declarative memory, Tulving (1972) has shown this type of memory to contain two separate types of memory: episodic and semantic memory.  Episodic memory is speculated to develop around three years of age (Burns et al, 2015) and involves memory of specific, personal events in a given time or place. Tulving (2002) described memory as being ‘mental time travel’ – that we must mentally travel back to the place in time to have a re-experiential moment (episodic retrieval) for episodic recall to count. Semantic memory on the other hand, refers to memory of factual and general knowledge and meanings. Distinction between episodic and semantic memory is seen through neurological diseases such as Alzheimer’s and semantic dementia. Early Alzheimer’s shows impaired episodic memory but preserved semantic memory and semantic dementia is the loss of semantic knowledge but preserved episodic memory in the early stages. Additionally, hippocampal damage at an early age has led to impaired episodic memory but intact ability to create new semantic memory (Vargha-Khadem et al, 1997). With non-declarative memory, it’s focus remains on our ‘memory abilities including skills and habits and priming and simple conditioning’ (Squire, 1992).

Evidence for distinguishing between short-term and long-term memory can be seen by Glanzer and Cunitz’s serial position curve (1966) as they investigated whether position of words in a list affected recall. In their experiment, participant showed greater recall of words from the beginning (primacy effect) and end (recency effect) of the word list but recalled the least from the middle. Explanations for the primacy effect were due to participants being able to rehearse words from beginning of the list which strengthened and transferred them to their long-term memory. The words learnt at the end of the list displaced the memory trace of the middle words, leaving only the words at the end of the list in the short-term memory slots.

The strongest evidence that short-term and long-term memory are separate stores is that of neurological evidence with patients with memory impairments. A major contributor to psychological research, especially with memory was HM (1926-2008), who suffered from severe epileptic seizures that prevented him from functioning adequately, so underwent a bilateral medial temporal lobe resection that resulted in his hippocampi being surgically removed. Consequently, HM suffered from anterograde amnesia, the inability to learn new information, therefore he couldn’t form new long-term declarative memories – a lack of consolidation results in inability to move information from one store to the other. Interestingly, HM’s short-term memory remained unimpaired, as he was able to learn new sensorimotor skills; for example, HM was shown a five-pointed star and asked to trace its outline but in the condition where he could only see his hand and the star was reflected in a mirror. HM learned the mirror-drawing skill within a few trials and became faster at drawing yet, at the end of testing, he had no recollection (no conscious memory) of having done the task prior (Milner, 1962; Squire, 2009). This has resulted in the discovery of procedural memory as HM remembered practising skills unconsciously.

Another example that supports the long-term systems is KF (1951-2014), who suffered specific damage to this episodic memory from a motorcycle accident that left him with the inability to form or recall personal events yet his semantic memory remained intact as he was able to recollect factual information – this supports the distinction between episodic and semantic memory. KF also demonstrates greater evidence as his short-term memory was impaired, whilst his long-term memory remained intact, highlighting how the stores are separate.

Overall, memory is a complex part of the brain and new research will always need to be untaken to create greater depth of our knowledge. Short-term memory can be differentiated simply from long-term through its smaller capacity and duration for holding information but are both crucially linked through storing and retrieving. Key evidence from brain impaired individuals furthers our understanding, however these cases are exceptional and rare, so case studies are difficult to generalise and come by. 

References

• APA Dictionary. Definition of memory. (https://dictionary.apa.org/memory) Accessed 23.05.19 
• Baddeley, A. (2000). The episodic buffer: a new component of working memory?. Trends in cognitive sciences, 4(11), 417-423.
• Baddeley, A. D., & Hitch, G. (1974). Working memory. In Psychology of learning and motivation (Vol. 8, pp. 47-89). Academic press.
• Burns, P., Russell, C., & Russell, J. (2015). Preschool children’s proto-episodic memory assessed by deferred imitation. Memory, 23(8), 1172-1192.
• Eysenck, M., & Keane, M. (2010). Cognitive Psychology (6th ed., pp. 205-223). Hove, Eng.: Psychology Press.
• Glanzer, M., & Cunitz, A. R. (1966). Two storage mechanisms in free recall. Journal of verbal learning and verbal behavior, 5(4), 351-360.
• Miller, G. A. (1956). The magical number seven, plus or minus two: Some limits on our capacity for processing information. Psychological Review, 63(2), 81.
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• Peterson, L., & Peterson, M. J. (1959). Short-term retention of individual verbal items. Journal of experimental psychology, 58(3), 193.
• Squire, L. R. (1992). Declarative and nondeclarative memory: Multiple brain systems supporting learning and memory. Journal of cognitive neuroscience, 4(3), 232-243.
• Squire, L. R. (2009). The legacy of patient HM for neuroscience. Neuron, 61(1), 6-9.
• Tulving, E. (1972). Episodic and semantic memory. Organisation of memory.
• Tulving, E. (2002). Episodic memory: From mind to brain. Annual Review of Psychology, 53, 1-25.
• Vargha-Khadem, F., Gadian, D.G., Watkins, K.E., Connelly, A., Van Paesschen, W., & Mishkin, M. (1997). Differential effects of early hippocampal pathology on episodic and semantic memory. Science, 227, 376-380.