As virtuous men pass mildly away,
And whisper to their souls to go,
Whilst some of their sad friends do say,
The breath goes now, and some say, No;

Memory is the mental process of storing and retrieving information in the brain. There are various levels of memory processing and different types of storing capacities that accompany each level. When information is received in the brain, it goes through several levels of sensory processing while it is stored; this is how human beings learn, by storing previously experienced environmental signals and comparing new ones to the ones already stored in the brain. The basic information-processing model for memory functioning is as follows:

Sensory Input Sensory Memory Short Term Memory Long Term Memory

As information progresses through each of these levels, there tends to be a greater chance for retention farther into the future.

Levels of Memory

  • Sensory Memory: Sensory memory is defined as the capacity to remember minute aspects and physical features of an object for very brief periods — most likely about a second or less. Due to this, sensory memory is almost indistinguishable from perception itself. This type of memory remains largely in theory; few analyses have been performed on information while it is in this stage of processing. The human mind cannot be directly aware of information while it exists in this level in the brain since it is so fleeting. It tends to be understood as the recognition of a perceptual whole, such as the brief memory of the experience of a faint sound or a briefly viewed image.

    • Iconic Memory: Sensory memory is broken down further to include visual sensory memory, which holds a visual stimulus for the span of about one second. One of the best examples of how iconic memory functions is to imagine how your brain responds when viewing a lightning bolt. The image flashes for only a brief moment, yet the form of the lightning will linger in iconic memory for a second or so after the stimulus is removed.

    • Echoic Memory: Another type of sensory memory is echoic memory, which accounts for sounds that have just been perceived. One of the easiest ways that this type of memory can be recognized is in the interpretation and processing of speech. As a word is pronounced by someone, we perceive it one syllable at a time. In order to grasp the whole word, each sound must be temporarily stored in the brain in order to more fully understand them later. If it weren't for this type of memory, then speech would be a disorganized chaos; humans would be unable to integrate information as it was delivered to them via speech.

  • Short Term Memory: Short term memory is very similar to sensory memory in that its capacity is very limited by both the amount of information that can be held in it and also the duration that information can be held. In order to illustrate the capacity of short term memory, try the following.

    Read the numbers below only once and then close your eyes and repeat them to yourself:

3 8 1 4 7 0 2

    More than likely, you had little difficulty recalling those pieces of information. Now, try reading the following different set of numbers once and closing your eyes to repeat them again:

1 6 2 9 0 4 3 7 2 5 1

    Most people with normal memory capacities cannot recall 11 pieces of information in succession after having read them only once. This is because these stimuli were stored in short term memory, which has a capacity of between 7 and 9 pieces of information for the average person.
    • Phonological short term memory: This is a type of short term memory that relies strongly on long term memory. Often when we are observing our surroundings, we will recognize certain objects, such as a tree, and we will think the word "tree." "Thinking" this word in this way is called a subvocal articulation, which is defined as an unspoken speech utterance. This is a manner of retaining information about our surroundings that integrate our language capacities with our perceptive faculties.
    Subvocal articulations can also be used when information is transferred from short term memory to long term memory. This process is called the articulatory loop, and is part of the newer theories of working memory, an expansion of short term memory. Basically, this occurs when a person attempts to remember a piece of information by repeating it to themselves as well as recalling a mental picture of that piece of information to enforce it both verbally and visually.

  • Long Term Memory: Long term memory holds information that is stored on a semi-permanent basis. There are no known limits on this type of memory. It occurs due to connections that are formed between neurons in the brain that are fairly static. Researchers argue that there can be strong connections between short term and long term memory. For example, the set of English characters "TXLKB" is much more easily recalled than the set of Greek characters "ΓΙΑΔΞ" (assuming that you're more knowledgeable of English than Greek, and have average memory capacities). This is because English letters have been learned by English-speaking people, and are stored in memory much more easily. This is related closely to phonological short term memory.
    • Kinesthetic Memory: When performing physical tasks such as writing and walking, a type of memory known as kinesthetic memory is used. This type of memory is still highly theoretical; it is difficult to apply limits to it due to the lack of clinical testing. It applies to sequences of movements of the muscles and their relationship to each other while in motion, which is all retained in these types of memories.2
    The articulatory loop is one process of encoding information into the long term memory. Further, there are two groups of long term memory processing.
    • Effortful Processing: As its name suggests, this type of memory processing refers to the ways in which we consciously try to remember something. When students use flash cards to stimulate their minds visually and verbally, this is one example of effortful long term memory processing.

Memory Conditions

  • Retrograde Amnesia: This condition involves the loss of previous long term memories, especially those concerning the individual's life. Often times, this is caused by a severe blow to the head. Usually this will result only in the loss of recent long term memories, rather than information that the person has known their whole lives. The reasons for this are still being researched.

  • Anterograde Amnesia: This condition results in a patient being unable to form new long term memories after the time of the brain damage. Usually, they will be able to remember information for a period of several minutes, but beyond that they are unable to retain anything (this is Leonard's condition in the film Memento, which is a good example of what this disorder is like). They are often able to discuss things that happened to them before their injury, but they will not even be able to remember people they've see daily since their brain damage.

  • Eidetic Memory or Photographic Memory: True to its name, individuals with photographic memories are able to recall events, objects, or information with extreme visual clarity. Some people experience similar types of memories when they have what is known as a flashbulb memory, an extremely lucid recollection of an event. However, individuals with photographic memories experience this all of the time. The transition between short term and long term memory is sometimes nonexistant for them, as they can often remember whatever they like without practicing the articulatory loop that many others do. Reasons for the existence of photographic memories are unknown. However, they are often tied to other conditions such as synesthesia, and I believe that it could be linked to a much more developed hippocampus; this is the area in the brain which controls memory.

1John Donne. A Valediction: Forbidden Mourning.
2Information on kinesthetic memory from Thanks to dutchess for reminding me of this type!


E. F. Loftus. Memory. © 1980; K. Haberlandt. Cognitive Psychology. © 1994; N. E. Spear. Memory: Phenomena and Principles. © 1994. — Node your library.
This is a node in progress. I'm thinking of adding a section regarding learning & long term memory, but I need to gather more of my notes together. Suggestions or additions for this? I'd love to hear them.