Memory

Memory refers to the mental systems and processes involved in storing and recalling information about stimuli that are no longer present, as well as to all of the information that is stored. Memory is essential to healthy human functioning, and it can be said that every mental process involves some aspect of memory. Indeed, the ancient Greek philosopher Cicero once described memory as "the treasury and guardian of all things." The human brain has evolved an enormous capacity for remembering, and in the course of life, people gather and store vast amounts of information. Memories of past experiences are necessary to understand new experiences, and to decide how to behave in unfamiliar situations. Without memory every person or situation we encountered would be strange and unfamiliar, and we could never learn from past experience. In fact, we would not be able to learn anything at all, since all learning requires remembering the material learned. Memory is also essential to a sense of self or identity, as memories of our past experiences, thoughts, and feelings inform us as to what we have done, who we have been, and who we are now. Memory can hold information ranging from how to put pants on, to the composition of the stars.

History

People have sought to understand the nature of memory since at least the time of the ancient Greek philosopher Plato, who is usually credited with the earliest serious discussion of it. He believed memory was like a blank slate on which accurate impressions of the world were made and preserved indefinitely. Plato distinguished two aspects of memory—the power to retain or keep information, and the power of recollection, or remembering information that is already present in memory. Plato's ideas still influence many contemporary psychological theories of memory contain these same beliefs.

During the Middle Ages, before the printing press, memory served as the vehicle through which history and knowledge were passed between people and generations. It seems having a good memory was greatly prized during the Middle Ages, and the improvement of memory skills was an important topic. A distinction was made between natural and artificial memory where natural memory was the memory abilities we were born with. They could not be trained and were thought to operate in a spontaneous, instinctive manner. On the other hand, artificial memory abilities were held to be trainable, and numerous systems were developed to improve them. As the printed word spread and the individual's memories became less essential in the transmission of knowledge the importance placed on memory by society apparently diminished. During the 1800s, educators also focused on training and exercising the memory. Memory was seen by many as being like a muscle that required exercise to remain fit. Thus memorization was thought to strengthen one's current memory system as well as future memorization skills, and rote memorization (memorizing information for no purpose other than to memorize it) was advocated for students. This view came under great criticism as the 1800s ended, and eventually the advocacy of rote memorization within the school system faded. Indeed, more recent research indicates that memorization for memorization's sake does not improve overall memory abilities in any observable way.

During the late 1800s the medical profession became interested in disorders of memory such as aphasia (a complete or partial impairment of the ability to understand or use words), and amnesia (generally, a partial or total loss of memory). The medical profession naturally focused on physiological and biological factors, and one of their most important findings was that aphasia was caused by lesions in the brain. This finding was of immense importance as it demonstrated for the first time that physiological and psychological functioning are connected.

Sigmund Freud, an Austrian physician who began his career in the 1890s, focused on psychological disorders that he felt were caused by memory disturbances. Freud felt mental illness occurs when unpleasant childhood memories are repressed, or kept from consciousness. His highly influential theory of psychoanalysis is in fact based on the concept that memories can be repressed, and he developed psychoanalytic therapy to uncover those memories and cure the patient.

The German psychologist, Hermann Ebbinghaus, carried out the first controlled experiments on memory in 1885, and in so doing set a pattern for modern experimental research on memory. Ebbinghaus developed many methods of studying memory that are still in use today. For example, he developed lists of nonsense syllables (one syllable groups of letters that have no meaning, e.g. "treb," "fug," or "duj"), that individuals would be asked to memorize. Ebbinghaus used nonsense syllables in an attempt to avoid the effects of previous learning, and associations the individual might have to meaningful words. Ebbinghaus would vary different aspects of the experiments to test different aspects of memory. For instance, he varied the lists by length to see how the number of syllables affected recall, and he would vary the amount of time between memorization and recall to see how the amount of time lapsed between learning and recall affected the amount of material recalled or forgotten.

Theories of basic memory processes

It is important to note that Ebbinghaus was working within the philosophical/psychological framework of associationism. With roots stretching back to Aristotle, associationism asserts that higher order mental processes, such as creativity or language, are produced by the combination of simpler mental processes, such as the mental association of objects, ideas, or experiences due to their similarity. Memory is said to be made up of associations between elements based on their similarity, contrast, or occurrence together in time or space. This implies a rather passive or inactive mind and memory, where the individual and their memory receives impressions and basically categorizes them according to their straightforward, objective characteristics. Remembering is simply reproducing these impressions and associations. Within this framework, when asked to remember and describe a rose, a person might "search" their memory for a specific representation of a rose or a specific experience with a rose, and use this to describe one.

This is in contrast to reconstructive theories of memory as proposed for example by William James in 1890, and by Sir Frederic Charles Bartlett in 1932. Within these theories, memory is seen as an active reconstruction and organization of past experiences that influences how new information is interpreted and organized, as well as how and what information is remembered. In contrast to associative theories, reconstructive theories of memory hold that abstract principles about new experiences and information are what is stored, not exact reproductions of the experiences themselves. During recall, specific memories are often reconstructed according to these general principles, they are not always reproductions of experience. Thus memory processes take an active role in what and how information is remembered. Within this framework, a person asked to remember and describe a rose might first access their general knowledge of plants, then flowers, then their knowledge of roses in general, and using this information, build or construct a description of a rose. In recent years, reconstructive theories of memory have gained favor as many psychologists believe that most mental processes, such as language and perception , are too complex to be explained by the combination of simple associative connections and reproductive memory.

Models of memory operation

Since memory and memory formation cannot be observed directly, various models have been put forth by memory researchers in an effort to clearly and simply describe how memory operates. In the early 1900s, psychologists proposed that memory was like a filing cabinet in that everything was categorized neatly and logically. In order to retrieve information, one simply and logically located the correct file folder. Later, as telephone systems were expanded, memory was likened to a telephone operator's switchboard with information coming in from many directions to a central source that sorted the information and decided on the appropriate output. With the development of the digital computer in the 1950s, psychologists began describing memory in terms of a computer model and focused on how the mind and memory might process information like computers do. This model has been highly influential, and since the 1950s researchers using this model have focused on the input and sequencing of information processing.

Three information processing systems

Most researchers divide memory's information processing operations into the stages of acquisition, consolidation, storage, and retrieval. Acquisition refers to the process the brain and the sensory organs use to bring information into the memory system. Consolidation is the process of organizing information to facilitate its storage in long-term memory. Storage describes the forming of a potentially permanent representation of information in the brain. Retrieval is the process of bringing stored information to consciousness. These processes are thought to occur within three largely accepted divisions of the memory processing system that are distinguished by the length of time information can be held, the amount of information that can be held, and the different processes that occur in each. The three stages are called sensory memory, short-term memory, and long-term memory. It should be noted that these systems are not presumed to occupy specific physical spaces within the brain. They are, more accurately, hypothesized systems distinguished by their varying characteristics.

Sensory memory

Sensory memory, or sensory register, notes or registers sensory stimuli as they are experienced. It consists of representations of the outside world as experienced through the senses such as touch , sight, or smell . It holds information for approximately one to two seconds. If, for instance, you glance at the ocean and turn away, the image of the ocean will be lost in one to two seconds unless the image is quickly transferred into the short-term memory system. The contents of sensory memory are constantly changing as new stimuli are perceived. Information that does not fade from sensory memory enters short-term memory.

Short-term memory

Short-term memory is thought to process information by actively repeating, grouping, and summarizing it to aid its storage in long-term memory. Information is thought to last within short-term memory for only a short period of time before it is either passed into long-term memory or discarded. For information to be transferred into long-term memory, it must be rehearsed or repeated.

Generally, short-term memory can hold five to nine units of information for between twenty seconds to one minute in length. It holds information for as long as its actively thought about, or until new information basically forces it out. Unless we repeat the information and purposely try to retain it, most, or all of it, will be lost. A good example of this process can be seen when you look up a new phone number, and repeat it to yourself as you dial it. After dialing it, within a few seconds you will usually forget it. Yet if you do this repeatedly (repetition or rehearsal), like for a friend with a new phone number, it will eventually enter long-term memory.

These "units" of information can represent single pieces of information, such as an individual's name, or the units can be single pieces of information that represent a number of different pieces of information, as in the last name of a family representing all of the family's members. The process of using a single item to represent a number of items is called chunking, and researchers have found that short-term memory's information holding capacity can be greatly enhanced with this process.

It seems there are many factors that determine what information enters long-term memory, two of the strongest being repetition and intense emotion. If something is repeated often enough, such as multiplication tables, it will enter long-term memory. And it is hard to forget intensely emotional experiences such as being involved in a serious car accident or falling in love.

Long-term memory

Long-term memory has been the focus of most research and theory on the memory system. It holds all the information that has managed to pass through the sensory and short-term memory systems. In contrast to both of those systems, long-term memory is thought to be able to hold potentially unlimited amounts of information for an indefinite period of time, possibly for a lifetime. It is thought to hold all of the memories of our life, as well as our knowledge of the world in general. In long-term memory one might find memories as diverse as the first person you ever had a crush on, knowledge of how to ride a bike or cook scrambled eggs, the names of the five great lakes of North America , or a second language. Indeed, long-term memory is often compared to an encyclopedia in terms of the amount and range of information it holds.

Long-term memory then stores and operates on very diverse types of information, and there are many theories as to how the different types of information are represented and organized within it. Research shows that long-term memory operates according to a number of different systems, and researchers disagree as to exactly how it should be divided up. Yet there are some very influential theoretical divisions of long-term memory that are now widely accepted. These are the divisions between procedural memory, episodic memory, and semantic memory.

Divisions of long-yerm memory

Procedural memory

Procedural memory is, as its name implies, knowledge of the steps necessary to perform certain procedures or activities. It is the knowledge of how to ride a bike or swim, how to cook spaghetti and meatballs, and even how to walk and run. Procedural learning is the acquisition of skills, such as learning how to operate a computer. How well something is learned is reflected in improved performance of the skill. It seems well-learned knowledge stored in the procedural memory system can be used without conscious awareness of the steps being performed. For instance, once a behavior is mastered—such as walking or driving a car—one rarely has to stop and think about what step comes next, and attention can be paid to other activities.

Often the information stored in procedural memory is difficult for the individual to articulate even though it is obvious from their smooth performance of the activity that they know it well. Procedural memories seem to last for a very long time, if not for a lifetime, and they are often very hard to change. Thus if one learns how to do something in a certain way, such as swim or play tennis, it can be very hard to change one's technique later.

Episodic memory

Episodic memory is the conscious recollection or remembering of specific experiences from a person's life. These memories often include the time and place of the experience, as well as a representation of the role the individual remembering played in it. An example of an episodic memory would be recalling the first time you operated a computer, including where and with whom, in contrast to how to operate a computer. Episodic memories seem to be more affected by the passage of time than are procedural or semantic memories such that if the event is not recalled and thought of relatively often, details of the event, if not the event itself, seems to fade or be forgotten over time.

Semantic memory

Semantic memory is all the easily articulated stored knowledge you have of the world in general that does not refer to specific events in your life. Examples of semantic memory involve factual knowledge such as knowing a car has four wheels, that a United States senator is elected to a term of four years, that Earth revolves around the Sun , or that giving a smile increases the odds of receiving a smile. Where procedural knowledge is knowing "how," semantic memory is knowing "that." Like procedural memory, semantic memory seems to last for a long time. It differs from procedural memory however, in that the knowledge can usually be articulated quite easily.

Exactly how the immense amount of information we acquire throughout life is stored or organized in semantic memory is still an active area of research. Most experts believe that, in general, information is stored in networks of related concepts. The more similar various concepts are, the more closely associated they will be in memory. Research in semantic memory does in fact indicate that it is organized such that when a certain idea is activated or brought to mind, related or similar items will be identified faster. For instance, if one is discussing roses, knowledge of other flowers and plants will be recalled faster and with more ease.

Mental representations in semantic memory

Two specific types of mental representations hypothesized to be used by the semantic memory system to organize information are schemas and categories. Schemas are ordered frameworks or outlines of world knowledge that help us organize and interpret new information. They are like maps or blueprints into which new related information will be fitted. Knowledge of your home town or city, with its streets, various buildings, and neighborhoods is an example of a schema.

Research shows that new information relating to knowledge one already has will be remembered better than information about a topic one has little or no knowledge of. Thus, if two people are given directions to a party, the individual who knows the layout of their city or town pretty well will tend to remember the directions to the party better than a person who has little or no knowledge of the city's layout. This is presumably because the person with the pre-existing knowledge is able to fit the new information into their older knowledge, and thus form a stronger link in memory.

Schemas also help to reconstruct, or try to remember, information that may have been forgotten. For example, if a friend brings up something that happened one time you both went out to eat dinner a few months ago and you don't remember it clearly, you might ask for more information, and then use your schema for the usual sequence of events in eating out to try to remember or reconstruct what happened. The accuracy of reconstructions is open to question.

Categories are another representational form of thought used by semantic memory to organize information. Categories are sets of objects, experiences, or ideas, that are grouped together because they are similar to one another in some respect. For example, apartments, houses, huts, and igloos, might be grouped under the category of dwellings. Like schemas, categories help us make sense of, and organize, the multitudinous aspects of the world.

Relations among memory systems in long-term memory

While it is thought that the procedural, episodic, and semantic memory systems operate relatively independently, it is obvious that they also interact and work together. For instance, one's procedural knowledge of how to ride a bike or operate a computer will be linked with one's semantic knowledge of how bikes and computers work in general. Moreover, episodic memories of, for instance, one's first date, will add to one's semantic knowledge of dating in general, and possibly one's procedural knowledge of how to best have a good time on a date.

Research methods

Most research on long-term memory is highly specialized, focusing on particular types of information storage and the various retrieval processes associated with them. In the research laboratory memory is most often assessed by recognition, recall, or relearning tasks.

In recognition tasks, research subjects are commonly shown lists of words or groups of visual stimuli, such as pictures of faces. After a period of time subjects are then presented with new lists or groups of visual stimuli in which some of the original material is embedded or mixed in. They are then asked to indicate which items they recognize from the original material. In order to assess different aspects of memory, researchers may vary the amount of material presented, how long they let the subject study it, how much time passes between presentation of the original and altered material, and any number of other variables. Recognition is often quite accurate, especially if the subject is asked only if they have seen an item before. An example of a recognition task in which the subject is asked to choose a correct answer from among incorrect ones is a multiple-choice test.

In recall tasks, subjects are asked to reproduce material that was previously learned. The material may consist of lists of words, stories, or visual stimuli. They may be asked to report the material in exactly the same way it was presented, or to report as much of the material as they can remember in any order at all (this is called "free recall"). In "cued recall" the subject is given clues to aid their recall. Giving clues can improve recall greatly. As in recognition tasks, many variables, such as the amount of material, and time between learning and testing, can be manipulated to test different aspects of memory. An essay test is an example of a recall task.

In relearning studies, the time it takes to learn material initially is compared to the time it takes to learn the same material a second time after it is forgotten. Findings consistently show relearning time is much less than original learning time. The difference between the two learning times is called the "savings score." The high savings scores found across almost all relearning studies indicates that once something is learned, it is never really forgotten completely. It seems some of the original learning remains, although how much and in what form remains unclear.

Reminding and forgetting

Reminding is an aspect of memory that indicates ideas are organized in long-term memory by similarity, whereby when people think of something, they are often reminded of a similar thing. Remindings are usually of information that is similar in content, or of earlier experiences that are similar to the current situation. The most widely accepted explanation of the reminding process is spreading activation which assumes memory is made up of networks of concepts that are connected due to similarity. When a concept from a network of concepts is used, that concept is presumably energized or activated in some way. This activation, if strong enough, spreads along the associative pathways connecting the activated concept to other related concepts and in turn activates the related concepts.

The spreading or activation process is seen as being largely automatic. It can, however, be controlled to a certain extent. In this way we can concentrate on current goals without being constantly distracted by related but largely irrelevant ideas.

Forgetting is the inability to recognize, recall, or reproduce information which was previously known or learned. Different theories within psychology propose various processes for how forgetting occurs. Traditional, associative learning theories believe forgetting is the decay of associative bonds through disuse, or not thinking of something. Associative theories also believe forgetting is caused by interference . Material will be retained to the extent that it was well-learned, unless previously or newly learned information interferes. Interference is the confusion or substitution of one item in memory with another. There are two types of interference: retroactive interference, when old information is harder to remember because new information gets in the way; and proactive interference, when new information is harder to learn because it is similar to old information. Interference theory holds that material is rarely lost or forgotten, it is simply unavailable or inaccessible.

Psychoanalytic theory, as discussed earlier, sees forgetting as the result of repression. Freud felt a good deal of forgetting happens because the forgotten material is associated with unpleasant experiences that produce anxiety which automatically evokes the defense mechanism of repression. Memories then are never truly lost, but are irretrievable due to repression.

The contemporary cognitive approach proposes that each of the three stages of information processing forgets or loses information for different reasons. In both the sensory and short-term memory systems, information is lost through decay of their underlying neural connections. Information is never really forgotten in long-term memory. It is assumed to be there but cannot be accessed due to a failure in retrieval.

It should be noted that there is no way to definitively discover whether information is retained for life or ever truly lost from memory. This is because even if someone cannot recall something that does not mean it is not present in memory. It may instead be inaccessible due to repression, interference, or retrieval failure. Moreover, it is often impossible to assess the accuracy of someone's individual memories as there are no available corroborative witnesses.

Memory disorders

The two main memory disorders are amnesia and aphasia. Amnesia is a partial or total loss of memory caused by emotional trauma, disease , or brain injury (usually due to head trauma, surgical accidents, or chronic alcohol abuse). Memory loss can occur for events just prior to the amnesia-causing incident (retrograde amnesia), or for events occurring after the incident (anterograde amnesia). In severe cases of anterograde amnesia, the person may be unable to form new memories, although recall of material learned before amnesia's onset is usually unaffected. Many cases of amnesia (even severe) are temporary, so that the person recovers his or her memory.

Aphasias are a complete or partial impairment of the ability to understand or use words which are caused by lesions in the brain. There are numerous varieties of aphasia, and diagnostic classification systems are constantly being revised.

Physiological basis

In recent decades, research on the physiological basis of human memory in the brain has intensified. Much has been learned about how information in memory is organized in the brain, and the roles various parts of the brain play in memory from research with those with amnesia or aphasia. In fact, detailed studies of individuals with unusual patterns of brain damage have produced much of our current knowledge about the physiological basis of human memory. It seems that numerous brain structures are involved in memory processing and various subtypes of memory. For instance, the ventromedial frontal region of the brain (an area in the lower front portion) seems to link memory and emotions, and the basal ganglia (a set of neural cell bodies set deep in the base of the cerebral hemispheres) are involved in learning new motor skills. Indeed, some researchers would argue that in a broad sense, one could say the entire brain is involved with some aspect of memory.

Current research/future developments

As in many other fields of psychology, research into underlying biological (physiological, genetic, hormonal) factors in mental phenomena is thriving. Studies concluded in the early and mid-1990s clearly show learning/memory mechanisms occur at synaptic connections—the site of information transfer between neurons. Dozens of different mutant learning/memory genes have already been identified which specifically block learning and/or short-term, amnesia-resistant, and long-term memory. Further studies will surely help uncover intricate mechanisms at the cellular and molecular level involved in learning and memory. Continual advances since the 1970s in brain-imaging techniques that allow non-intrusive visualization of the brain at work have contributed immensely to this area of research. Improvement in brain imaging techniques such as computed tomography, positron emission tomography, and functional magnetic resonance imaging (MRI) , development of new techniques, and neurobiological and genetic research will undoubtedly lead to exciting discoveries about the basis of memory and other mental functions in the brain.

Resources

books

Gregg, V.H. Introduction to Human Memory. New York: Routledge, 1986.

Lutz, J. Introduction to Learning and Memory. Pacific Grove, CA: Brooks-Cole, 1994.

McGaugh, J.L., N.M. Weinberger, and G. Lynch, eds. Brain Organization and Memory: Cells, Systems and Circuits. New York: Oxford University Press, 1992.

Morris, P.E., and M.E. Conway, eds. The Psychology of Memory. Vols. 1-3. New York: New York University Press, 1993.

Marie Doorey

KEY TERMS

Associationism

—A philosophical/psychological stance holding that mental associations are the building blocks of complex mental processes such as language and memory.

Brain imaging techniques

—High technology techniques allowing non-intrusive visualization of the brain, these include computed tomography, positron emission tomography, and functional magnetic resonance imaging.

Category

—A set of objects, experiences, or ideas, grouped together because of their similarity, they aid the organization of information in memory.

Episodic memory

—Memory system holding conscious recollections of events from a person's life that often include time, place, and a representation of oneself.

Long-term memory

—Part of memory system capable of holding large amounts of information for an indefinite period of time, possibly for a lifetime.

Memory

—All of the information retained by an individual, and the mental systems and processes involved in storing and recalling information.

Neuron

—Nerve cell.

Procedural memory

—Memory system holding often hard to articulate knowledge of how to perform certain procedures or activities.

Reconstructive memory

—Type of memory thought to store experiences by abstract principles, which are then used to reconstruct memories during recall.

Schema

—A structured framework of world knowledge that helps organize and interpret new information, as well as reconstruct information that may have been forgotten.

Semantic memory

—Memory system holding all the easily articulated knowledge of the world an individual has that does not refer to particular events in their life.

Sensory memory

—Part of the memory system that registers experience through the senses, holding onto information for one to two seconds before it is lost or transferred to short-term memory.

Short-term memory

—Part of the memory system that repeats and organizes information to aid its storage in long-term memory, it is able to hold only limited amounts of information for short periods of time before it is either lost, or transferred to long-term memory.