GlossaryMemoryMemory refers to the storage, retention and recall of information including past experiences, knowledgeand thoughts. Memory for specific information can vary greatly according to the individual and theindividuals state of mind. It can also vary according to the content of the information itself; thusinformation which is novel or exciting tends to be better remembered than information which isuninteresting or ordinary. Failure of memory can normally result from failure to adequately store thememory in the first place, failure to retain the information (forgetting), and failure to retrieve theinformation later.The precise biological mechanisms of memory are not fully understood, but most scientists believe thatmemory results from changes in connections or connection strengths between neurons in the brain.One possible mechanism is long-term potentiation (LTP). Roughly stated, LTP refers to a processwhereby if two neurons are usually active together, the connection between them will be strengthened;over time, this means that activity in one neuron will tend to produce activity in the other neuron.Categories of Memory SystemsPsychologists and memory researchers often divide memory into categories defined by the duration forwhich the memory is expected to last.Sensory memory refers to the fact that, after experiencing a stimulus, information about that stimulus isbriefly held in memory in the exact form it was received, until it can be further processed. Typically,sensory memories may last only a few seconds before decaying -- or being overwritten by new,incoming information. But, while they last, sensory memories contains detailed information: almost likean internal "copy" of the stimulus, in perfect detail. For example, psychologists have assumed that thereis a memory area (called a "buffer") where incoming visual information is stored as a picture or icon.This is sometimes called iconic memory. While visual information remains in iconic memory, anindividual can answer detailed questions, such as what is the third row of numbers in a numericaldisplay. Psychologists have assumed that there is also an echoic memory for auditory information(stored as an echo) and other buffers for information related to the other senses: taste, smell and touch.Short-term memory refers to memories which last for a few minutes. Unlike sensory memory, which isstored in the exact form it was experienced, short-term memory has received some processing; thus,"A" is stored not as a visual stimulus, but as an abstract concept of the letter "A". Short-term memory isof limited capacity, usually 5-9 items ("7-plus-or-minus-two"). Beyond this capacity, new information can"bump" out other items from short-term memory. This is one form of forgetting. Objects in short-termmemory can be of indefinite complexity: thus short-term memory can hold several numbers, or severalwords, or several complex concepts simultaneously. Thus, while an individual may only be able toremember seven random digits, it may be possible to remember more digits if they are "chunked" intomeaningful objects: thus, "1776-2001-1941" represents twelve separate digits -- well beyond mostpeoples capacity -- but only three easily-remembered chunks.Items can be maintained indefinitely in short-term memory by rehearsal: e.g. by repeating theinformation over and over again. An example would be a seven-digit phone number, which ismaintained in short-term memory by repetition until the number is dialed, and then fades from short-term memory once the conversation starts. Repetition may also increase the probability that items inshort-term memory will enter permanent storage in long-term memory.Intermediate-term or working memory is sometimes considered a synonym for short-term memory.However, memory researchers often consider this a specialized term referring for information about thecurrent task. Thus, even though a specific phone number may occupy short-term memory, workingmemory contains the information that lets you remember that you are in the process of phoning the gascompany to complain about a recent billing error.Long-term memory is memory that lasts for years or longer. It contains everything we know about the
world, including semantic and factual information as well as autobiographical experience. In general,long-term memory is organized so that it is easy to reach a stored item by a number of routes. Forexample, the concept "umbrella" may be retrieved by seeing an umbrella, experiencing a rainstorm,hearing the words to the song "Let a smile be your umbrella," and so on. Retrieval of an item alsofacilitates other related items: so that retrieving information about a cat can lead to retrieval ofinformation about dogs, lions, specific instances of cats (Grandmothers tabby), the Cheshire Cat fromAlice in Wonderland, and so on.NOTE: Clinicians (e.g. neurologists) often use a slightly different classification, in which short-termmemory is memory for events which occurred recently (e.g. a few days or weeks ago) and long-termmemory is memory for events which occurred in the distant past (e.g. childhood).Kinds of Long-term MemoryThere are several different ways to classify long-term memories according to their content.Declarative memory is a term for information which is available to conscious recollection and verbalretrieval (i.e., it can be "declared"). Two subclasses of declarative memory are episodic memory, whichis autobiographical information, and semantic memory, which is factual information about the world(vocabulary items, knowledge of what a hammer is used for, memory of multiplication tables, etc.).Brain Structures involved in Long-Term MemoryMost types of memory appear to be stored in the cortex. Different areas of cortex specialize in differentkinds of information, so that visual information about the Statue of Liberty may be stored in one location(e.g., the inferior temporal cortex), while information about its associations to liberty and immigrationmight be stored in another (e.g., the frontal cortex). High linkage between these two areas means thatseeing a picture of the Statue of Liberty can retrieve memory about its associations. At the same time,damage to specific areas of cortex can produce specific memory deficits. For example, damage to aspecific region within the temporal lobe can produce a memory deficit in which the patient losesknowledge about "living things" (e.g. dogs, lions, birds) but maintains knowledge about other categories(e.g. inanimate objects such as furniture and utensils).Formation of new declarative memories depends on the hippocampus and related structures inthemedial temporal lobe. When these structures are damaged, a condition of anterogradeamnesiacan result, in which older declarative memories are largely spared, but few if any newdeclarative memories are acquired. At this point, the process whereby the hippocampus and othermedial temporal lobe structures contribute to long-term memory formation is still incompletelyunderstood. Some researchers believe that the hippocampus acts as a temporary store for newinformation, which is then gradually transferred to permanent storage in the cortex. Other researchersbelieve that the hippocampus never actually stores information itself, but is needed by the cortex in theprocess of developing new memories.Another important structure is the amygdala, which lies near the hippocampus in the medial temporallobes. The amygdala is critically involved in emotional memory; an individual with damage to theamygdala may remember the details of a traumatic (or joyful) event but not the emotional content of thatevent.Pathology of MemoryMemory can be impaired by various injuries and diseases. Damage to the medial temporal lobe andhippocampus can devastate the ability to acquire new declarative memory; damage to the storageareas in cortex can disrupt retrieval of old memories and interfere with acquisition of new memories --simply because there is nowhere to put them.Another critical factor is attention. Items are more likely to be remembered if they are attended to in thefirst place; this is why novel or exciting items are more likely to be remembered than dull or ordinary
The problem is exacerbated by age (I’m not talking about advanced age — I’m afraid certain aspectsof cognitive processing begin to decline as early as the 30s).Part of the problem is also that we tend to believe that we don’t need to do anything to maintain athought, particularly when it has “popped” into our minds easily. But current estimates are thatunrehearsed information lingers in working memory for less than two seconds!Some of these problems are dealt with in my article on action slips(these problems are not, strictlyspeaking, a failure of memory, but a failure in attention), and in my e-book on Rememberingintentions.But in this article I want to talk about another aspect: the relationship between working memory, andattention (and, as it happens, intelligence!).In my article on working memory and intelligence I talk about the difference between crystallized andfluid intelligence — that fluid intelligence is probably a better measure of what we think of as“intelligence”, and that working memory capacity is often used synonymously with fluid intelligence.A new theory is that the relationship between working memory and fluid intelligence is due to theability to control attention.This theory emphasizes the role of attention in keeping information active (i.e. in working memory),and argues that working memory capacity is not, as usually thought, about the number of items oramount of information that can be held at one time. Instead, it reflects the extent to which a personcan control attention, particularly in situations where there is competing information / demands.I have to say that this makes an awful lot of sense to me. I can’t, in the space I have here, go into allthe evidence for and against the theory, but here’s one situation which is interesting. The “cocktailparty phenomenon” is a well-known method in psychology, whereby people are given two streams ofaudio, one for each ear, and instructed to listen only to one. At some point, the person’s name isspoken into the unattended stream, and about a third of people pick that up. In a recent take of thatclassic study, researchers compared the performance of people as a function of their workingmemory capacity. Only 20% of those with a high capacity heard their name in the unattendedchannel compared to 65% of low-capacity people. The point being that a critical aspect of goodattentional control is the ability to block our irrelevant information.This ability is one that we already know is worsened by increasing age.The message from all this, I guess, is that: short-term memory problems are, by and large, attention problems. attention involves both the ability to keep focused on the information you want to keep active, and the ability to not be distracted by competing and irrelevant stimuli. you need to actively attend to keep information active, particularly as you get older.
many of us over-estimate how much information we can keep active at one time.And if you want strategies to help you keep more information active, I suggest you look at improvingyour ability to chunk, condense and label information. If you can reduce a chunk of information to asingle label quickly, all you need to do is remember the label. (I explain all this at length in mybook The Memory Key, but I’m afraid it needs far too much explanation to go into here).Anyway, I hope this helps those of you (most of us!) with short-term memory problems.This article originally appeared in the April 2005 newsletter.References: 1. Heitz, R.P., Unsworth, N. & Engle, R.W. 2004. Working memory capacity, attention control, and fluid intelligence. In O. Wilhelm & R,W. Engle (eds.) Handbook of Understanding and Measuring Intelligence. London: Sage Publicationhttp://www.memory- key.com/problems/everyday_problems/stm-problems .