Long-Term Memory

Long-Term Memory Definition

Memory is a cognitive process that humans use every day, and without it, humans wouldn't survive. Memories are central to making sense of the present and thinking of the future. Without memory, we wouldn't be able to learn anything.

The Americal Psychological Society defines in its dictionary memory as:

Examples of Long-Term Memory

Since long-term memory is so important for human survival, it can be seen in a wide range of daily-life events. Remembering your way to school is an example of long-term memory. Other examples of long-term memory are learning how to drive or play an instrument and learning from that one time when you were a kid when you got stung by a nettle. Remembering such an event would allow you not to walk into a nettle again and will support your safety.

Types of Long-Term Memory

Endel Tulving was one of the first cognitive psychologists to point out that the unitary structure of Long-Term Memory (LTM) proposed in the Multi-store Model by Atkinson and Shiffrin (1968) is too simple and inflexible. In 1972, Tulving suggested three types of LTM: episodic memory, semantic memory, and procedural memory. Later in 1980, Cohen and Squire further categorized LTM into explicit and implicit memory. The graph below shows the full structure of LTM:

Explicit Memory

Explicit memory, also known as declarative memory, is the ‘knowing that’ memory. Explicit memory involves conscious efforts to be stored and recalled. Explicit memory includes semantic Memory and Episodic Memory.

Semantic Memory

Semantic memory is the memory for facts and knowledge, such as information about the world. Semantic memory might be compared to a combination of encyclopaedia and dictionaries as a metaphor. Semantic memory is stored in the form of meaning and concept.

Episodic Memory

Episodic memory is the memory of specific events that we have experienced in our lives. As a metaphor, episodic memory might be compared to a daily diary. Episodic memory is time-stamped. Each episodic memory will include multiple elements: specific details of the event (e.g. time, place, people, etc.), the context, and the emotion are woven into one memory. Episodic memory also requires conscious effort to recall.

Implicit Memory

Implicit memory, also known as procedural memory, is the “knowing how” memory. Implicit memory does not involve conscious efforts to be stored or recalled.

Procedural Memory

Procedural memory is the memory of skills and behaviours. Procedural memory is formed without time stamps and is stored in the form of motor action. We can recall procedural memories without conscious awareness or effort, such as playing the piano or riding a bike. Since we can recall procedural memories without conscious awareness, procedural memories can include skills that we would find hard to explain, such as teaching others how to swim if we have already mastered swimming.

Evaluation of the Types of LTM

Let’s evaluate the evidence we have regarding LTM. Clinical studies of amnesia, such as HM and Clive Wearing, showed patients have difficulties recalling personal events in the past. Yet, their semantic memories were relatively unaffected.

In the case of Clive Wearing, the client was a professional musician and could play the piano without difficulty. However, he could not remember having learned to play after suffering a brain injury. This suggests an impaired episodic memory but functioning procedural memory. Both cases support the view that there are separate memory stores for LTM.

Fig. 2. Individual playing the piano and exerting procedural memory.

Neuroimaging Support for LTM

Brain scanning studies provide evidence to support the idea of different LTM stores. For example, Tulving et al. (1994) asked participants to perform different memory tests while having a brain scan with a PET scanner. The results imply that episodic and semantic memories were located in the prefrontal cortex (PEC).

Real-life Application of LTM

Understanding different types of memory allow for the development of helpful real-world applications. Belleville et al. (2006) researched a group of older people suffering from mild cognitive impairment. The researcher compared participants who received memory training with a control group that did not. Findings show that participants in the experimental group outperformed the control on an episodic memory test. Researchers concluded that psychologists could have a better opportunity to improve people's lives by devising appropriate treatments and interventions by categorising the different types of LTM.

Problems in Long-Term Memory

Supporting evidence drawn from clinical cases lacks control and has insufficient sample sizes. Clinical cases such as Clive Wear's allow researchers to examine memory in a way that would be impossible in laboratory settings. However, there are problems generalising the findings of these clinical case studies with one or a few individuals to explain how memory works in the general population. Drawing firm conclusions from clinical case studies may overlook some unknown and specific issues that can explain other individuals' behaviour. This raises serious concerns about the generalisability of clinical findings.

The similarity between types of LTM suggests they may not be truly distinct enough to be categorised into three types. Also, there is a link between semantic and procedural memory. For example, we can produce automatic languages and talk fluently using semantic concepts without consciously recalling the details of each semantic idea. These studies revealed that a clear distinction between the three types of LTM is not a firm conclusion.

The capacity of Long-Term Memory

Capacity refers to one of the memory features. It refers to the amount of information that the long-term memory system contains.

The capacity of long-term memory has been explained in terms of neuronal connections. Given that the neuron connections cannot be unlimited, it is logical that long-term memory capacity is also not unlimited. However, there are billions of neural connections in the human brain. Given these facts, psychologists work with the assumption that long-term memory capacity is unlimited, although researchers acknowledge that there could be a limit to it.

Fig. 3. Depiction of the unlimited number of neuronal connections.

Duration of Long-Term Memory

Duration is another feature of memory. Duration refers to the amount of time that learned information can be recalled. Research has suggested that long-term memory duration is influenced by two factors: memory encoding and memory retrieval.

1. In regards to encoding, it has been suggested that if learning takes place at a superficial level, forgetfulness is more likely to take place. For a memory to be stored for a longer time in long-term memory, encoding is meant to take place at a deep level.
2. In terms of retrieval, it has been suggested that the more a piece of information is retrieved from long-term memory, the more it is repeated and practised. This, in turn, has a positive impact on long-term memory duration.