Memories come in many different forms. There is much that researchers do not understand about human memory and how it works.

This article explores the types of memory and what a person can do to improve their recall.

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There are many theories about the types of memory within the human brain. Most scientists believe there are at least four general types of memory:

  • working memory
  • sensory memory
  • short-term memory
  • long-term memory

Some researchers suggest these are not distinct types of memory, but rather stages of memory.

In this view, memory begins in sensory memory, transitions to short-term memory, and then may move to long-term memory.

A memory a person uses only for a brief time, such as a word they use at the beginning of a sentence, is a part of working memory and may never move to another part of memory.

Some brain scientists divide these types of memory into more specific categories.

Sensory memory holds sensory information for very brief periods of time, usually 1 second or less. The processing of memories and other information begins in this type of memory.

If a person pays attention to sensory input, then the information may move into short-term and then long-term memory.

Some examples of sensory memory include:

  • registering the sounds a person encounters on a walk
  • briefly acknowledging something in a person’s field of vision

Sensory memory helps a person piece together a sense of the world based on recent sights, sounds, and other sensory experiences.

When a specific sensory experience becomes relevant, such as the smell of something in the kitchen, it may move to other types of memory.

Otherwise, sensory memories are very short-term, and a person quickly forgets them.

For example, a person will not recall all the specific sounds they heard in the last 30 seconds, 30 minutes, or 30 days unless there is some reason to remember them.

Short-term memory allows a person to recall a limited string of information for a short period.

These memories disappear quickly, after about 30 seconds .

Short-term memory is not just memory that does not last long. Instead, it is a type of short-lived storage that can only hold a few pieces of information.

Some examples of short-term memory include:

  • remembering a string of 5–7 words and repeating it back
  • remembering a phone number while getting a pen to jot it down

Working memory is similar to short-term memory. However, unlike the latter, working memory is where a person manipulates information.

This helps them remember details of their current task. Some behaviors that use working memory include:

  • solving a complex math problem where a person must remember several numbers
  • baking something, which requires a person to recall the ingredients they already added
  • participating in a debate, during which a person must remember the main arguments and the evidence each side uses

While researchers typically separate working and short-term memory into two different categories, research often finds a significant overlap between the two.

Long-term memory stores a wide range of memories and experiences.

Most memories that people recall, especially those older than about 30 seconds, are part of long-term memory.

Many researchers divide long-term memory into two subcategories: implicit and explicit.

Explicit long-term memory

Explicit memories are conscious memories of events, autobiographical facts, or things a person learns.

Some types of explicit long-term memory include the following.

Episodic memory

These are memories of events or autobiographical facts. Examples of episodic memory include remembering an election, events from childhood, and personal facts, such as if someone is married.

Semantic memory

Semantic memories are general knowledge about the world. A person may remember a fact or event that they did not experience because they learned or studied it.

For instance, knowing what the human heart looks like is an example of semantic memory. However, it would be an episodic memory if the person can remember dissecting a pig heart in school.

Implicit long-term memory

Implicit memories are memories that influence a person’s behavior. However, people do not consciously think about them.

Some types of this memory include the following.

Procedural memory

Procedural memory helps a person perform familiar tasks, such as walking or driving.

At first, they might have to learn to do these things and remember specific skills, but eventually, these tasks become an automatic part of procedural memory.

Priming

Priming occurs when experiences influence a person’s behavior.

For example, a smoker might crave a cigarette after a meal, or an experimenter might train a person to press a button in response to a photo.

Classical and operant conditioning both prime people or animals to perform specific behaviors in response to certain experiences.

Working, sensory, and short-term memory have smaller capacities. This is because these types of memories only last for a short period.

With short-term memory, there is usually a specific limit on how much information a person can retain — usually about seven items.

Some people could increase their short-term memory capacity with practice.

The brain is not a computer, and memories do not take up physical space. In theory, there is no specific limit on the capacity of long-term memory .

However, the quality of memories and their details may vary and change with time.

Memories may be unreliable

The brain does not record memories perfectly, so memories may change or disappear with time.

Numerous studies suggest that memories are not reliable, even when a person remembers something very clearly.

In one 2015 study, researchers were able in just a few hours to convince innocent people they had committed serious crimes, such as assault with a weapon, in their teenage years.

Can someone have a photographic memory?

Some people have unusually good memories. People with hyperthymesia , an extraordinarily rare condition, may remember all or most autobiographical memories.

Others may practice memory skills to become better at memorizing information or recalling strings of words or numbers.

There is no scientific evidence anyone has a so-called photographic memory. The brain is not a camera and cannot perfectly record information.

Some strategies for improving memory include:

  • Developing mnemonic devices for remembering new information. For example, remembering all the names in a room could involve making up a rhyme or an association for each name.
  • Doing brain teasers and challenging puzzles.
  • Developing strong memory associations to help remember things. Talking about recent memories or journaling can help cultivate these associations.
  • Doing cardiovascular exercise to promote brain health.

The memory is a complex system, not a single organ or process.

A person may improve their memory by adopting a healthful lifestyle and practicing strategies specifically designed to promote recall.

People concerned about their memory should see a doctor, as any unexplained changes could signal a range of medical conditions.