What Is Long-Term Memory?

The Duration, Capacity, and Types of Long-Term Memory

Long-term memory
Long-term memory has a large capacity and long duration.. Baris Simsek / E+ / Getty Images

Long-term memory refers to the storage of information over an extended period. If you can remember something that happened more than just a few moment ago whether it occurred just hours ago or decades earlier, then it is a long-term memory.

This information is largely outside of our awareness, but can be called into working memory to be used when needed. Some of this information is relatively easy to recall while other memories are much harder to access.

Not all long-term memories are created equal, however. Information that is of greater importance leads to a stronger recall.

You can usually remember important events such as your wedding day or the birth of your first child with much greater clarity and detail than you can less memorable days. While some memories spring to mind quickly, other are weaker and might require prompts or reminders to bring them into focus.

Memories that are frequently accessed also become much stronger and easier to recall. Accessing these memories over and over again strengthens the neural networks in which the information is encoded, leading to easier recollection of the information. On the other hand, memories that are not recalled often can sometimes weaken or even be lost or replaced by other information.

The Duration and Capacity of Long-Term Memory

Through the process of association and rehearsal, the content of short-term memory can become long-term memory.

While long-term memory is also susceptible to the forgetting process, long-term memories can last for a matter of days to as long as many decades.

There are a number of factors that can influence how long information endures in long-term memory. First, the way the memory was encoded in the first place can play a significant role.

If you were very aware and alert when you had the experience, then the memory will probably be a lot more vivid.

As mention earlier, the number of times you access a memory can also play a role in the strength and duration of a memory. Not surprisingly, memories that you have to recall often tend to stick around and become much stronger. This is why repeating information over and over while you are studying leads to better recall on an exam.

Types of Long-Term Memory

Long-term memory is usually divided into two types - declarative (explicit) memory and non-declarative (implicit) memory.

  • Explicit memories, also known as declarative memories, include all of the memories that are available in consciousness. Explicit memory can be further divided into episodic memory (specific events) and semantic memory (knowledge about the world).
  • Implicit memories are those that are mostly unconscious. This type of memory includes procedural memory, which involves memories of body movement and how to use objects in the environment. How to drive a car or use a computer are examples of procedural memories.

    Long Term Memories Change

    The information-processing model of memory characterizes human memory as much like a computer. Information enters short-term memory (a temporary store) and then some of this information is transferred into long-term memory (a relatively permanent store), much like information being saved to the hard disk of a computer. When information is needed, it is called forth out of this long-term storage using environmental cues, much like accessing a saved folder on your computer.

    Recent research suggests that memories are not saved in a static state and then pulled up with perfect clarity, however, as the information-processing model seems to suggest. Researchers have found that memories are transformed every single time a they are accessed.

    Neurons first encode memories in the cortex and hippocampus. Each time a memory is recalled, it is then re-encoded by a similar, but not identical, set of neurons. Accessing memories often helps make them stronger, yet the research has found that this re-encoding can have an impact on how the information is remembered. Subtle details may change, and certain aspects of the memory may be strengthened, weakened, or even lost altogether depending up which neurons are activated.

    While long-term memory has a seemingly boundless capacity and duration, these memories can also be surprisingly fragile and susceptible to change, misinformation, and interference. Memory expert Elizabeth Loftus has demonstrated how easily false memories can be triggered. In one of her most famous experiments, she was able to get 25 percent of her participants to believe in a false memory that they had once been lost in a shopping mall as a child.

    Why is long-term memory so susceptible to these inaccuracies? In some cases, people miss important details about events. To fill in these missing "gaps" in information, the brain sometimes fabricates details that seem to make sense. In other instances, old memories can interfere with the formation of new ones, making it difficult to recall what actually happened.

    Learn more about some of the major problems with memory, the top reasons why we forget things, and a few of the tricks you can use to improve your long-term memory.

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