Memory

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In psychology, memory is an organism's ability to store, retain, and subsequently recall information. Although traditional studies of memory began in the realms of philosophy, the late nineteenth and early twentieth century put memory within the paradigms of cognitive psychology. In recent decades, it has become one of the principal pillars of a new branch of science called cognitive neuroscience, a marriage between cognitive psychology and neuroscience.

Contents 1 Processes 2 Classification 2.1 Sensory 2.2 Short-term 2.3 Long-term 3 Models 3.1 Multi-store 3.2 Working memory 3.3 Levels of processing 4 Classification by information type 5 Classification by temporal direction 6 Physiology 7 Disorders 8 Memorization 9 Popular culture 10 References 11 See also 12 External links

Processes

There are several ways to classify memories, based on duration, nature and retrieval of information. From an information processing perspective there are three main stages in the formation and retrieval of memory:

• Encoding or registration (processing and combining of received information)
• Storage (creation of a permanent record of the encoded information)
• Retrieval or recall (calling back the stored information in response to some cue for use in a process or activity)

Classification

A basic and generally accepted classification of memory is based on the duration of memory retention, and identifies three distinct types of memory: sensory memory, short term memory and long term memory.

Sensory

Sensory memory corresponds approximately to the initial 200 - 500 ms after an item is perceived. The ability to look at an item, and remember what it looked like with just a second of observation, or memorization, is an example of sensory memory. With very short presentations, participants often report that they seem to "see" more than they can actually report. The first experiments exploring this form of sensory memory were conducted by George Sperling using the "partial report paradigm." Subjects were presented with a grid of 12 letters, arranged into three rows of 4. After a brief presentation, subjects were then played either a high, medium or low tone, cuing them which of the rows to report. Based on these partial report experiments, Sperling was able to show that the capacity of sensory memory was approximately 12 items, but that it degraded very quickly (within a few hundred milliseconds). Because this form of memory degrades so quickly, participants would see the display, but be unable to report all of the items (12 in the "whole report" procedure) before they decayed. This type of memory cannot be prolonged via rehearsal.

Short-term

Some of the information in sensory memory is then transferred to short-term memory. Short-term memory allows one to recall something from several seconds to as long as a minute without rehearsal. Its capacity is also very limited: George A. Miller, when working at Bell Laboratories, conducted experiments showing that the store of short term memory was 7±2 items (the title of his famous paper, "The magic number 7±2"). Modern estimates of the capacity of short-term memory are lower, typically on the order of 4-5 items, and we know that memory capacity can be increased through a process called chunking. For example, if presented with the string:

FB IPH DTW AIB M

people are able to remember only a few items. However, if the same information is presented in the following way:

FBI PHD TWA IBM

people can remember a great deal more letters. This is because they are able to chunk the information into meaningful groups of letters. Beyond finding meaning in the acronyms above, Herbert Simon showed that the ideal size for chunking letters and numbers, meaningful or not, was three. This is evidenced by the tendency to remember phone numbers as several chunks of three numbers with the final four-number groups generally broken down into two groups of two.

Short-term memory is believed to rely mostly on an acoustic code for storing information, and to a lesser extent a visual code. Conrad (1964)^[1] found that test subjects had more difficulty recalling collections of words that were acoustically similar (e.g. dog, fog, bog, log).

Long-term

The storage in sensory memory and short-term memory generally have a strictly limited capacity and duration, which means that information is available for a certain period of time, but is not retained indefinitely. By contrast, long-term memory can store much larger quantities of information for potentially unlimited duration (sometimes a whole lifespan). Whilst short-term memory encodes information acoustically, long-term memory encodes it semantically. Baddeley (1966)^[2] found that after 20 minutes, test subjects had the greatest difficulty recalling a collection of words that had similar meanings (e.g. big, large, great, huge).

Short-term memory is supported by transient patterns of neuronal communication, dependent on regions of the frontal lobe (especially dorsolateral prefrontal cortex) and the parietal lobe. Long-term memories, on the other hand, are maintained by more stable and permanent changes in neural connections widely spread throughout the brain. The hippocampus is essential to the consolidation of information from short-term to long-term memory, although it does not seem to store information itself. Rather, it may be involved in changing neural connections for a period of three months or more after the initial learning.

One of the main functions of sleep is thought to be to improve consolidation of information, as it can be shown that memory depends on getting sufficient sleep between training and test, and that the hippocampus replays activity from the current day while sleeping. For example, if we are given a random seven-digit number, we may remember it for only a few seconds and then forget, which means it was stored into our short-term memory. On the other hand, we can remember telephone numbers for many years through repetition; those long-lasting memories are said to be stored in our long-term memory.

Models

Models of memory provide abstract representations of how memory is believed to work. Below are several models proposed over the years by various psychologists.

Multi-store

The multi-store model was first described in 1968 by Atkinson and Shiffrin.

The multi-store model has been criticized for being too simplistic. For instance, long-term memory is believed to be actually made up of multiple subcomponents, such as episodic and procedural memory. It also proposes that rehearsal is the only mechanism by which information eventually reaches long-term storage, but evidence shows us capable of remembering things without rehearsal (flashbulb memory).

Working memory

In 1974 Baddeley and Hitch proposed the working memory model which further subdivides short-term memory into a number of sub-stores and processes. In this model, STM consists of three basic stores: the central executive, the phonological loop and the visuo-spatial sketchpad.

The central executive essentially acts as attention, channeling information to the phonological loop and the visuo-spatial sketchpad, which act as "slave systems".

The phonological loop stores sound information by silently rehearsing sounds or words in a continuous loop; the articulatory process (the "inner voice") continuously "speaks" the words to the phonological store (the "inner ear"). The phonological loop has a very limited capacity, which is demonstrated by the fact that it is easier to remember a list of short words (e.g. dog, wish, love) than a list of long words (e.g. association, systematic, confabulate) because short words fit better in the loop. However, if the test subject is given a task that ties up the articulatory process (saying "the, the, the" over and over again), then a list of short words is no easier to remember.

The visuo-spatial sketchpad stores visual and spatial information. It is engaged when performing spatial tasks (such as judging distances) or visual ones (such as counting the windows on a house).

The working memory model explains many practical observations, such as why it is easier to do two different tasks (one verbal and one visual) than two similar tasks (eg two visual), and the aforementioned word-length effect. However, the concept of a central executive as noted here has been criticized as inadequate and vague.

Levels of processing

Craik and Lockhart (1972) proposed that it is the method and depth of processing that affects how an experience is stored in memory, rather than rehearsal.

• Organisation - Mandler (1967) gave participants a pack of word cards and asked them to sort them into any number of piles using any system of categorisation they liked. When they were later asked to recall as many of the words as they could, those who used more categories remembered more words. This study suggested that the act of organising information makes it more memorable.
• Distinctiveness - Eysenck and Eysenck (1980) asked participants to say words in a distinctive way, e.g. spell the words out loud. Such participants recalled the words better than those who simply read them off a list.
• Effort Tyler et al. (1979) had participants solve a series of anagrams, some easy (FAHTER) and some difficult (HREFAT). The participants recalled the difficult anagrams better, supposedly because they put more effort into them.

Classification by information type

Long-term memory can be divided into declarative (explicit) and procedural (implicit) memories. (Anderson, 1976)

Declarative memory requires conscious recall, in that some conscious process must call back the information. It is sometimes called explicit memory, since it consists of information that is explicitly stored and retrieved.

Declarative memory can be further sub-divided into semantic memory, which concerns facts taken independent of context; and episodic memory, which concerns information specific to a particular context, such as a time and place. Semantic memory allows the encoding of abstract knowledge about the world, such as "Paris is the capital of France". Episodic memory, on the other hand, is used for more personal memories, such as the sensations, emotions, and personal associations of a particular place or time. Autobiographical memory - memory for particular events within one's own life - is generally viewed as either equivalent to, or a subset of, episodic memory. Visual memory is part of memory preserving some characteristics of our senses pertaining to visual experience. We are able to place in memory information that resembles objects, places, animals or people in sort of a mental image. Visual memory can result in priming and it is assumed some kind of perceptual representational system or PRS underlies this phenomenon. [1]

In contrast, procedural memory (or implicit memory) is not based on the conscious recall of information, but on implicit learning. Procedural memory is primarily employed in learning motor skills and should be considered a subset of implicit memory. It is revealed when we do better in a given task due only to repetition - no new explicit memories have been formed, but we are unconsciously accessing aspects of those previous experiences. Procedural memory involved in motor learning depends on the cerebellum and basal ganglia.

So far, nobody has successfully been able to isolate the time dependence of these suggested memory structures.

Classification by temporal direction

A further major way to distinguish different memory functions is whether the content to be remembered is in the past, retrospective memory, or whether the content is to be remembered in the future, prospective memory. Thus, retrospective memory as a category includes semantic memory and episodic/autobiographical memory. In contrast, prospective memory is memory for future intentions, or remembering to remember (Winograd, 1988). Prospective memory can be further broken down into event- and time-based prospective remembering. Time-based prospective memories are triggered by a time-cue, such as going to the doctor (action) at 4pm (cue). Event-based prospective memories are intentions triggered by cues, such as remembering to post a letter (action) after seeing a mailbox (cue). Cues do not need to be related to the action (as the mailbox example is), and lists, sticky-notes, knotted handkerchiefs, or string around the finger (see box) are all examples of cues that are produced by people as a strategy to enhance prospective memory.

Physiology

Overall, the mechanisms of memory are not well understood. Brain areas such as the hippocampus, the amygdala, or the mammillary bodies are thought to be involved in specific types of memory. For example, the hippocampus is believed to be involved in spatial learning and declarative learning. Damage to certain areas in patients and animal models and subsequent memory deficits is a primary source of information. However, rather than implicating a specific area, it could be that damage to adjacent areas, or to a pathway traveling through the area is actually responsible for the observed deficit. Further, it is not sufficient to describe memory, and its counterpart, learning, as solely dependent on specific brain regions. Learning and memory are attributed to changes in neuronal synapses, thought to be mediated by long-term potentiation and long-term depression.

Disorders

Much of the current knowledge of memory has come from studying memory disorders. Loss of memory is known as amnesia. There are many sorts of amnesia, and by studying their different forms, it has become possible to observe apparent defects in individual sub-systems of the brain's memory systems, and thus hypothesize their function in the normally working brain. Other neurological disorders such as Alzheimer's disease can also affect memory and cognition.

While not a disorder, a common temporary failure of word retrieval from memory is the tip-of-the-tongue phenomenon.

Impaired memory can be a symptom of hypothyroidism.

Memorization

Memorization is a method of learning that allows an individual to recall information verbatim. Rote learning is the method most often used. The Spacing effect shows that an individual is more likely to remember a list of items when rehearsal is spaced over an extended period of time. In contrast to this is cramming which is intensive memorization in a short period of time. Also relevant is the Zeigarnik effect which states that people remember uncompleted or interrupted tasks better than completed ones.

In March 2007 it was reported that German researchers found they could use odors to re-activate new memories in the brains of people while they slept and the volunteers remembered better later.^[3]

Popular culture

• Marcel Proust's novels deal extensively with memory.
• The experimental film Memento emulates the experience of not being able to convert short-term memories into long-term memories.
• Memory plays a central role in the video game series, 'Kingdom Hearts.'
• The short stories of Philip K. Dick and the movies based on those works deal extensively with the nature of memory and the consequences to society if memories can be artificially generated.
• Strange Days (film) is a film about memory. New technology allows people to record all the sensory data associated with their experiences. Playing back one of these recordings is like exactly reliving moments. Lenny, the character played by Ralph Fiennes, is still in love with his ex-girlfriend, played by Juliette Lewis. He keeps replaying recorded memories of their time together. Lenny's friend Mace played by Angela Bassett tells him to stop, saying, "Memories fade. They're made that way for a reason."
• Eternal Sunshine of the Spotless Mind is a film about removing a person from one's memory; all events shared with this person are erased through a medical procedure.
• Thanks For the Memory, an episode of Red Dwarf, deals with the consequences of implanted memories.
• Andrew Lloyd Webber's musical Cats includes a famous song entitled Memory.
• In Final Fantasy Crystal Chronicles, most of the storyline revolves around memories.
• 50 First Dates is a film about a girl who, after a tragic accident, cannot form short-term memory for more than a day.

The sci-fi shows 'Stargate SG-1' and 'Atlantis' have several episodes concerning memory.

• The show Psych deals with a detective that has extraordinary powers of observation and also a photographic memory.

References

See also

• Aging and memory
• Alzheimers
• Amnesia
• Attention versus memory in prefrontal cortex
• Autobiographical memory
• Cellular memory
• Dementia
• Emotion and memory
• The Persistence of Memory
• False Memory
• Forgetting curve
• Giordano Bruno
• Hebbian learning
• Involuntary Memory
• Kinesthetic learning
• List of memory biases
• Long-term potentiation
• Memory inhibition
• The Memory-Prediction Framework - an acclaimed "unifying theory of memory"
• MemoryArchive, a wiki collecting memories
• Mindfulness
• Misinformation effect
• Mnemonic
• Muscle memory or proprioception - the sense and memory of how parts of the body are trained to move
• Neural adaptation
• Source amnesia
• Synaptic plasticity
• Tip-of-the-tongue
• Visual memory

Wikipedia information about Memory This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Memory". It may not have been reviewed by professional editors (see full disclaimer). Help contribute to Americola and edit this article.