Memory: Definition, Stages and Types

To remember events, events, or processes, we have to commit them to memory; forming a memory involves encoding, storing, retaining, and, later, recalling information and past experiences.

Cognitive psychologist Margaret W. Matlin described it as the process of retaining information over time; others have defined it as the ability to use our past experiences to determine our future path. When asked to explain memory, most people think of studying for a test or remembering where we put the car keys. However, memory is essential in our daily lives; we could not function in the present or move forward without trusting her.

What is memory?

It is the ability to encode, store, retain, and subsequently remember information and past experiences in the human brain; it can be thought of in general terms as the use of expertise or events that affect or influence current behavior.

Memory is the total of what we remember, and it gives us the ability to learn and adapt from previous experiences, as well as to build relationships. It is the ability to recall past experiences and the power or process to remember previously learned facts, experiences, impressions, skills, and habits. It is the reserve of things learned and retained from our activity or experience, as evidenced by modifying the structure or behavior or memory and recognition.

In more physiological or neurological terms, memory is, in its simplest form, a set of neural connections encoded in the brain; it is the recreation or reconstruction of past experiences by the synchronous firing of neurons that were involved in the background, without however, as we will see, because of the way it is encoded, it is perhaps best thought of as a kind of collage or puzzle, rather than in the traditional way as a collection of stored recordings or images or video clips. Our memories are not stored in our brains like books on library shelves but are reconstructions on the fly of items scattered throughout various areas of our brain.

Memory storage

Stages of memory

Memory encoding

When information enters our memory system (from sensory input), it must be changed into a form that the system can handle so that it can be stored; think of this as something similar to changing your money into a different currency when traveling from country to country, for example, a word seen (in a book) can be stored if it is changed (encoded) into a sound or meaning (i.e., semantic processing).

There are three main ways that information can be encoded (changed):

1. Visual (image)

2. Acoustic (sound)

3. Semantics (meaning)

For example, how do you remember a phone number you have looked up in the phone book? If you can see it, you are using visual encoding, but if you repeat it to yourself, you are using acoustic (by sound) encoding.

Evidence suggests that this is the primary coding system in short-term memory; acoustic coding. When a person is presented with a list of numbers and letters, they will try to retain them (verbally). The essay is a verbal process regardless of whether the list of items is presented acoustically (someone reads them) or visually (on a sheet of paper).

In long-term memory, the primary encoding system appears to be semantic encoding (by meaning). However, information can also be encoded both visually and acoustically.

Memory storage

This refers to the nature of memory stores:

  • Where information is stored.
  • How long the memory is (duration).
  • How long it can be held at any one time (capacity).
  • What type of information is stored.

How we store information affects how we retrieve it, there has been a great deal of research on the differences between short-term and long-term memory.

Most adults can store 5-9 items in their short-term memory. Miller (1956) raised this idea and called it the magic number. He thought that the short-term memory capacity was 7 (plus or minus 2) items because it only had a certain number of “spaces” in which things could be stored.

However, Miller did not specify the amount of information that can be kept in each slot; if we can “group” information together, we can store much more information in our short-term memory; on the contrary, the capacity is unlimited.

Memory recall

This refers to removing information from storage; if we cannot remember something, it may be because we cannot recover it; when they ask us to salvage something from memory, the differences between short and long term become evident.

A short memory is stored and recalled sequentially; for example, if a group of participants is given a list of words to remember and then asked to remember the fourth word on the list, the participants review the list in the order in which they heard it to retrieve the information.

Long-term memory is stored and retrieved by association, so you can remember what you went up for if you go back to the room where you first thought about it.

Organizing the information can help the retrieval of the help; you can collect the information in sequences (for example, alphabetically, by size, or by time). Imagine a patient discharged from the hospital whose treatment consisted of taking several pills at different times, changing his bandage, and doing exercises; if the doctor gives you these instructions in the order in which they should be carried out during the day (i.e., in a sequence of time), this will help the patient to remember them.

Memory types

While experts have different definitions for short-term memory, it is generally described as the recall of things that happened immediately up to a few days; in general, it is believed that five to nine items can be stored in active memory in the short term and can be quickly recovered. Patients suffering from short-term memory loss cannot remember who entered the room five minutes earlier, but they can place their childhood friend from 50 years ago.

Explicit memory

It is one of the two main subdivisions of long-term memory; it requires conscious thinking, like remembering who came to dinner last night or naming animals that live in the jungle, which is what most people have in mind when they think of “memory And if yours is good or bad, it is often associative; your brain joins memories together. For example, when you think of a word or occasion, like a car, your memory can show a host of associated memories, from carburetors to your daily commute to your family or thousands of other things.

Semantic memory

It is not connected to personal experience and includes common knowledge, such as state names, letter sounds, capitalization of proper names and countries, and other facts that are not in question. Some examples of semantic memory include:

  • Just knowing that the sky is blue.
  • Learning how to use a knife and fork.

episodic memory

It is the unique memory of a person of a specific event or episode; people can generally associate particular details with episodic memory, such as how they felt, the time and place, and other details, it is not clear why some memories of events in our lives are memory-compromised, while others are not recorded, but researchers believe that emotions play a critical role in what we remember.

Some examples of episodic memory:

  • Where were you and the person you were meeting?
  • Your beach vacation last summer.
  • The first time you traveled by plane.
  • Your first day at a new job.
  • The restaurant you went to on your first date with your spouse.

Implicit memory

Sometimes called unconscious or automatic, past experiences are used to remember things without thinking about them, and musicians and professional athletes are said to have a superior ability to form procedural memories.

While the implicit requires little or no effort to remember, the explicit, sometimes called declarative, requires a more concerted effort to bring up the surface. Read more about implicit memory (required article)

Procedure memory

It is a subset of implicit memory; it is a part that goes in the long run responsible for knowing how to do things, also known as motor skills; you do not have to dig through your memory to remember how to walk every time you take a step.

Some procedural examples:

  • Playing the piano.
  • Ice skating.
  • Playing tennis.
  • Swimming.
  • Climbing stairs.

It is the kind of implicit memory that allows us to carry out commonly learned tasks without consciously thinking about them; it is our knowledge of how riding a bike, tying a shoe, and washing dishes are all tasks that require procedural memory, even what we consider “Natural” tasks, such as walking, require procedural memory. Although we can do such tasks quite quickly, it is often difficult to verbalize exactly how we do it. Read more about procedure memory (required article)

You probably use a different part of the brain than episodic memory – with brain injuries, you can lose one skill without losing the other. A person who has experienced amnesia and forgets a lot about his personal life often retains procedural memory – how to use a fork or drive a car, for example.


It can also come from priming; you are “prepared” by your experiences if you have heard something recently or many times that something else is ready to remind you more quickly. For example, if you were asked to name an American city that begins with the letters “Ch,” you would most likely respond Chicago unless you have a close personal connection or recent experience with another city “Ch” (Charlotte, Cheyenne, Charleston…) because you’ve heard of Chicago more often.

In the brain, the neural pathways that represent the things we have experienced most often are more critical than those for which we have the least. Long-term memory can weaken with age or with cognitive conditions as with short-term memory. For example, it may be more challenging to complete a previously relatively straightforward procedure for you; you may forget a step to bake a cake that you have baked hundreds of times and that you thought was firmly committed.

Autobiographical memory

From the moment of birth, each of us is exposed to a world full of sensations and information; all of these experiences (first kisses, soft summer breezes, familiar places, sad goodbye) have the potential to end up as autobiographical memories.

Not all of them do, of course. Scientists have always been interested in understanding what we remember about our past and why we remember it, but finding a way to study autobiographical memory presents a problem. Many other types of memory are tested in the laboratory using carefully planned experiments, which do not work so well for autobiographical “episodic” memories, which are made over time and everywhere.

The 19th century English psychologist Sir Francis Galton pioneered a simple method for studying autobiographical memory, a modified version of which is still used today; he decided to go fishing, so to speak, in search of memories associated with a list of common everyday words, four times he threw his web of words, using the same cues to try to capture his memories.

One of Galton’s findings was that it was difficult to pin down when the events he remembered occurred; another was that his brain often produced the same associations repeatedly. “This shows much less variety in the mental inventory of ideas than I expected,” he wrote, “and makes us feel like the paths of our minds are wearing down in very deep ruts. Read more about autobiographical memory   (required article)

Memory and Morpheus

Many researchers may disagree with Shakespeare’s suggestion that sleep stirs the senses into oblivion. Instead, they believe that sleep actively helps our brains consolidate what we learn and remember.

To be clear, not all researchers agree on the role of sleep in memory consolidation. But the research in favor of the power of sleep may be growing. Read more about memory and Morpheus (required article)

Sleep rhythms

Experts distinguish between two broad categories of sleep based, in part, on measurable brain wave patterns using the EEG. Delta waves, the slowest rhythm of all brain waves, predominate during the deepest part of non-rapid eye movement sleep; meanwhile, REM (rapid eye movement) sleep, the type of sleep most often associated with sleepy, is characterized by bursts of quick eye movements. In a good night’s sleep, non-REM and REM sleep alternate cyclically.


While non-REM and REM sleep is critical to cognitive functioning, they can be crucial in encoding and consolidating different types of memories. Non-REM rest can be particularly significant for declarative memory, our ability to recall the kinds of fact-based information we might try in school. Meanwhile, REM sleep has been associated with procedural memory for knowing how to ride a bike or learn a new dance step.

Studies suggest that depriving people of adequate sleep hampers their ability to learn new information – for example, Harvard Medical School researchers found that one night of sleep deprivation reduces activity in the hippocampus, resulting in poorer memory retention.

And sleeping after learning something seems to help the brain consolidate new information in long-term memory. In one of their studies on sleep, researcher Kenichi Kuriyama and his colleagues had participants rest one night after doing a finger-tapping task on a computer keyboard for 12 minutes; they found that participants’ performance improved the next day significantly on parts of the job that had been most difficult for them.

Georgia Tarrant
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Hello, how are you? My name is Georgia Tarrant, and I am a clinical psychologist. In everyday life, professional obligations seem to predominate over our personal life. It's as if work takes up more and more of the time we'd love to devote to our love life, our family, or even a moment of leisure.