1. Attention: Attention guides our focus to select what’s most relevant for our lives and is normally associated with novelty. Nothing focuses the mind like surprise. For example, although one may thoroughly enjoy a particular conversation, the same conversation a second time around would be dull. Emotional intensity acts to narrow the scope of attention so that a few objects are emphasized at the expense of many others. Focusing upon a very narrow area allows for an optimal use of our limited attentional capacity.
2. Consolidation of a memory: Most of the information we acquire is forgotten and never makes it into long-term memory. When we learn a complex problem, the short-term memory is freed up and the action becomes automatic. Emotionally charged events are remembered better than those of neutral events. (link is external) You will never forget some events, such as the joy of the birth of your first child, or the horror of the 9/11 terrorist attack. The stress hormones, epinephrine and cortisol, enhances memory and consolidates memory contents. In evolutionary terms, it’s logical for us to imprint dangerous situations with extra clarity so that we may avoid them in the future.
3. Memory recall: Memories of painful emotional experiences linger far longer than those involving physical pain. There is an old saying that “sticks and stones can break your bones, but words can never hurt you.” To the contrary, evidence shows that hurt feelings could be worse than physical pain. In the words of Maya Angelou: “I've learned that people will forget what you said, people will forget what you did, but people will never forget how you made them feel.” In fact, there is an evidence that acetaminophen (e.g., Tylenol) works not only on physical pain, but also on emotional pain.
4. Priming: Past memories are often triggered or primed by one’s environment. Priming refers to activating behavior through the power of unconscious suggestion. Researchers (link is external)have found that people who were made to think of self-discipline (by having to unscramble sentences about it) immediately made more future-oriented snack choices than those given sentences about self-indulgence. In this case, the goal stored in long-term memory is retrieved and placed in short-term (or working) memory. Similarly, the concept of a library causes people to speak more softly.
5. Mood memory: Our current emotional state facilitates recall of experiences that had a similar emotional tone. When we are in a happy mood, we tend to recall pleasant events and vice versa. This is because moods bring different associations to mind. For example, recalling positive childhood experiences while in a good mood. Being in a bad mood primes a person to think about negative things.
6. Blanking out: Stress can lead to memory deficit, such as the common experience of mentally blanking during a high-pressure examination or interview. Thus, worrying about how you will perform on a test may actually contribute to a lower test score. In general, anxiety influences cognitive performance in a curvilinear manner (an inverted U-curve). This phenomenon is known as the Yerkes– Dodson law (link is external). That is, when levels of arousal are too low (boredom) and when levels of arousal are too high (anxiety or fear) performance is likely to suffer. Under situations of low arousal, the mind is unfocused. In contrast, under situations of high stimulation, the focus of attention is too narrow, and important information may be lost. The optimal situation is moderate arousal.
7. Duration neglect (Peak-End rule) (link is external): The way we remember events is not necessarily made up of a total of every individual moment. Instead, we tend to remember and overemphasize the peak (best or worst) moment and the last moment, and neglect the duration of an experience (link is external). This explains why normally the bad ending ruins the whole experience. For example, when you remember your summer vacation to Canada, there is just too much information to evaluate whether it was an enjoyable trip. So, you apply the peak-end rule and you more heavily weight the best moment and the most recent moment.
Since the early neurological work of Karl Lashley and Wilder Penfield in the 1950s and 1960s, it has become clear that long-term memories are not stored in just one part of the brain, but are widely distributed throughout the cortex. After consolidation, long-term memories are stored throughout the brain as groups of neurons that are primed to fire together in the same pattern that created the original experience, and each component of a memory is stored in the brain area that initiated it (e.g. groups of neurons in the visual cortex store a sight, neurons in the amygdala store the associated emotion, etc). Indeed, it seems that they may even be encoded redundantly, several times, in various parts of the cortex, so that, if one engram (or memory trace) is wiped out, there are duplicates, or alternative pathways, elsewhere, through which the memory may still be retrieved. The indications are that, in the absence of disorders due to trauma or neurological disease, the human brain has the capacity to store almost unlimited amounts of information indefinitely. Forgetting, therefore, is more likely to be result from incorrectly or incompletely encoded memories, and/or problems with the recall/retrieval process. It is a common experience that we may try to remember something one time and fail, but then remember that same item later. The information is therefore clearly still there in storage, but there may have been some kind of a mismatch between retrieval cues and the original encoding of the information. “Lost” memories recalled with the aid of psychotherapy or hypnosis are other examples supporting this idea, although it is difficult to be sure that such memories are real and not implanted by the treatment. Theorists disagree over exactly what becomes of material that is forgotten. Some hold that long-term memories do actually decay and disappear completely over time; others hold that the memory trace remains intact as long as we live, but the bonds or cues that allow us to retrieve the trace become broken, due to changes in the organization of the neural network, new experiences, etc, in the same way as a misplaced book in a library is “lost” even though it still exists somewhere in the library.
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Research using functional magnetic resonance imaging (fMRI) suggests that verbs and nouns are stored in different ways in the brain.
Concrete nouns are stored in areas of the brain used to sense or manipulate the referent objects, leading to a theory of meaning based largely on function.
Increasing forgetfulness is a normal part of the ageing process, as the neurons in ageing brains lose their connections and start to die off, and, ultimately the brain shrinks and becomes less effective. The hippocampus, which as we have seen is crucial for memory and learning, is one of the first areas of the brain to deteriorate with age. Recent studies in mice involving infusions of blood from young mice into older mice have shown that the old mice that received young blood showed a significant burst of brain cell growth in the hippocampus region (and vice versa), leading to speculation that young blood might represent the antidote to senile forgetfulness (and other ravages of old age). Similar studies on humans with Alzheimers disease are currently in progress. Interestingly, it appears NOT to be possible to deliberately delete memories at will, which can have negative consequences, for example if we experience traumatic events we would actually prefer to forget. In fact, such memories tend to be imprinted even more strongly than normal due to their emotional content, although recent research involving the use of beta blockers (such as propanonol) suggests that it may be possible to tone down the emotional aspects of such memories, even if the memories themselves cannot be erased. The way this works is that the act of recalling stored memories makes them "malleable" once more, as they were during the initial encoding phase, and their re-storage can then be blocked by drugs which inhibit the proteins that enable the emotional memory to be re-saved.
Biological way of consolidating memories
Consolidation is the processes of stabilizing a memory trace after the initial acquisition. It may perhaps be thought of part of the process of encoding or of storage, or it may be considered as a memory process in its own right. It is usually considered to consist of two specific processes, synaptic consolidation (which occurs within the first few hours after learning or encoding) and system consolidation (where hippocampus-dependent memories become independent of the hippocampus over a period of weeks to years).
Neurologically, the process of consolidation utilizes a phenomenon called long-term potentiation, which allows a synapse to increase in strength as increasing numbers of signals are transmitted between the two neurons. Potentiation is the process by which synchronous firing of neurons makes those neurons more inclined to fire together in the future. Long-term potentiation occurs when the same group of neurons fire together so often that they become permanently sensitized to each other. As new experiences accumulate, the brain creates more and more connections and pathways, and may “re-wire” itself by re-routing connections and re-arranging its organization.
As such a neuronal pathway, or neural network, is traversed over and over again, an enduring pattern is engraved and neural messages are more likely to flow along such familiar paths of least resistance. This process is achieved by the production of new proteins to rebuild the synapses in the new shape, without which the memory remains fragile and easily eroded with time. For example, if a piece of music is played over and over, the repeated firing of certain synapses in a certain order in your brain makes it easier to repeat this firing later on, with the result that the musician becomes better at playing the music, and can play it faster, with fewer mistakes.
In this way, the brain organizes and reorganizes itself in response to experiences, creating new memories prompted by experience, education or training. The ability of the connection, or synapse, between two neurons to change in strength, and for lasting changes to occur in the efficiency of synaptic transmission, is known as synaptic plasticity or neural plasticity, and it is one of the important neurochemical foundations of memory and learning.
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Reading out loud (or even whispering or mouthing it) forms auditory links in our memory pathways, as well as visual ones from looking a a page or screen.
So, we remember ourselves producing and saying the information as well as reading it visually, which may improve our overall retrieval of memories.
But this process works best, when just SOME of the information (e.g. the most important words or concepts) is read out loud, and the rest not, as this takes advantage of the “oddball effect” whereby we remember the more unusual or distinctive information best.
It should be remembered that each neuron makes thousands of connections with other neurons, and memories and neural connections are mutually interconnected in extremely complex ways. Unlike the functioning of a computer, each memory is embedded in many connections, and each connection is involved in several memories. Thus, multiple memories may be encoded within a single neural network, by different patterns of synaptic connections. Conversely, a single memory may involve simultaneously activating several different groups of neurons in completely different parts of the brain.
The inverse of long-term potentiation, known as long-term depression, can also take place, whereby the neural networks involved in erroneous movements are inhibited by the silencing of their synaptic connections. This can occur in the cerebellum, which is located towards the back of the brain, in order to correct our motor procedures when learning how to perform a task (procedural memory), but also in the synapses of the cortex, the hippocampus, the striatum and other memory-related structures.
Contrary to long-term potentiation, which is triggered by high-frequency stimulation of the synapses, long-term depression is produced by nerve impulses reaching the synapses at very low frequencies, leading them to undergo the reverse transformation from long-term potentiation, and, instead of becoming more efficient, the synaptic connections are weakened. It is still not clear whether long-term depression contributes directly to the storage of memories in some way, or whether it simply makes us forget the traces of some things learned long ago so that new things can be learned.
Sleep (particularly slow-wave, or deep, sleep, during the first few hours) is also thought to be important in improving the consolidation of information in memory, and activation patterns in the sleeping brain, which mirror those recorded during the learning of tasks from the previous day, suggest that new memories may be solidified through such reactivation and rehearsal.
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Studies have shown that information is transferred between the hippocampus and the cerebral cortex during deep sleep, and sleep appears to be essential for the proper consolidation of long-term memories.
However, even daytime naps can help improve memory to some extent, and helps with the memorization of important facts.
Memory re-consolidation is the process of previously consolidated memories being recalled and then actively consolidated all over again, in order to maintain, strengthen and modify memories that are already stored in the long-term memory. Several retrievals of memory (either naturally through reflection, or through deliberate recall) may be needed for long-term memories to last for many years, depending on the depth of the initial processing. However, these individual retrievals can take place at increasing intervals, in accordance with the principle of spaced repetition (this is familiar to us in the way that “cramming” the night before an exam is not as effective as studying at intervals over a much longer span of time).
The very act of re-consolidation, though, may change the intial memory. As a particular memory trace is reactivated, the strengths of the neural connections may change, the memory may become associated with new emotional or environmental conditions or subsequently acquired knowledge, expectations rather than actual events may become incorporated into the memory, etc.
Research into a cognitive disorder known as Korsakoff’s syndrome shows that the retrograde amnesia of sufferers follows a distinct temporal curve, in that the more remote the event in the past, the better it is preserved. This suggests that the more recent memories are not fully consolidated and therefore more vulnerable to loss, indicating that the process of consolidation may continue for much longer than initially thought, perhaps for many years.
Biology of recalling memories
Recall or retrieval of memory refers to the subsequent re-accessing of events or information from the past, which have been previously encoded and stored in the brain. In common parlance, it is known as remembering. During recall, the brain "replays" a pattern of neural activity that was originally generated in response to a particular event, echoing the brain's perception of the real event. In fact, there is no real solid distinction between the act of remembering and the act of thinking.
These replays are not quite identical to the original, though - otherwise we would not know the difference between the genuine experience and the memory - but are mixed with an awareness of the current situation. One corollary of this is that memories are not frozen in time, and new information and suggestions may become incorporated into old memories over time. Thus, remembering can be thought of as an act of creative reimagination.
Because of the way memories are encoded and stored, memory recall is effectively an on-the-fly reconstruction of elements scattered throughout various areas of our brains. Memories are not stored in our brains like books on library shelves, or even as a collection of self-contained recordings or pictures or video clips, but may be better thought of as a kind of collage or a jigsaw puzzle, involving different elements stored in disparate parts of the brain linked together by associations and neural networks. Memory retrieval therefore requires re-visiting the nerve pathways the brain formed when encoding the memory, and the strength of those pathways determines how quickly the memory can be recalled. Recall effectively returns a memory from long-term storage to short-term or working memory, where it can be accessed, in a kind of mirror image of the encoding process. It is then re-stored back in long-term memory, thus re-consolidating and strengthening it.
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Several studies have shown that both episodic and semantic memories can be better recalled when the same language is used for both encoding and retrieval.
For example, bilingual Russian immigrants to the United States can recall more autobiographical details of their early life when the questions and cues are presented in Russian than when they are questioned in English.
The efficiency of human memory recall is astounding. Most of what we remember is by direct retrieval, where items of information are linked directly a question or cue, rather than by the kind of sequential scan a computer might use (which would require a systematic search through the entire contents of memory until a match is found). Other memories are retrieved quickly and efficiently by hierarchical inference, where a specific question is linked to a class or subset of information about which certain facts are known. Also, the brain is usually able to determine in advance whether there is any point in searching memory for a particular fact (e.g. it instantly recognizes a question like “What is Socrates’ telephone number?” as absurd in that no search could ever produce an answer).
There are two main methods of accessing memory: recognition and recall. Recognition is the association of an event or physical object with one previously experienced or encountered, and involves a process of comparison of information with memory, e.g. recognizing a known face, true/false or multiple choice questions, etc. Recognition is a largely unconscious process, and the brain even has a dedicated face-recognition area, which passes information directly through the limbic areas to generate a sense of familiarity, before linking up with the cortical path, where data about the person's movements and intentions are processed. Recall involves remembering a fact, event or object that is not currently physically present (in the sense of retrieving a representation, mental image or concept), and requires the direct uncovering of information from memory, e.g. remembering the name of a recognized person, fill-in the blank questions, etc.
Recognition is usually considered to be “superior” to recall (in the sense of being more effective), in that it requires just a single process rather than two processes. Recognition requires only a simple familiarity decision, whereas a full recall of an item from memory requires a two-stage process (indeed, this is often referred to as the two-stage theory of memory) in which the search and retrieval of candidate items from memory is followed by a familiarity decision where the correct information is chosen from the candidates retrieved. Thus, recall involves actively reconstructing the information and requires the activation of all the neurons involved in the memory in question, whereas recognition only requires a relatively simple decision as to whether one thing among others has been encountered before. Sometimes, however, even if a part of an object initially activates only a part of the neural network concerned, recognition may then suffice to activate the entire network.
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Colour may have an effect on our ability to memorize something.
People remember colour scenes better than black-and-white ones, although only if naturally (as opposed to falsely) coloured.
In particular, warm colours, like red, yellow and orange, may help us to memorize things by increasing our level of attention (our ability to select from information available in the environment). The more attention is focused on outside stimuli, the greater the likelihood of those stimuli being stored in long-term memory.
In the 1980s, Endel Tulving proposed an alternative to the two-stage theory, which he called the theory of encoding specificity. This theory states that memory utilizes information both from the specific memory trace as well as from the environment in which it is retrieved. Because of its focus on the retrieval environment or state, encoding specificity takes into account context cues, and it also has some advantages over the two-stage theory as it accounts for the fact that, in practice, recognition is not actually always superior to recall. Typically, recall is better when the environments are similar in both the learning (encoding) and recall phases, suggesting that context cues are important. In the same way, emotional material is remembered more reliably in moods that match the emotional content of these memories (e.g. happy people will remember more happy than sad information, whereas sad people will better remember sad than happy information).
According to the levels-of-processing effect theory, another alternative theory of memory suggested by Fergus Craik and Robert Lockhart, memory recall of stimuli is also a function of the depth of mental processing, which is in turn determined by connections with pre-existing memory, time spent processing the stimulus, cognitive effort and sensory input mode. Thus, shallow processing (such as, typically, that based on sound or writing) leads to a relatively fragile memory trace that is susceptible to rapid decay, whereas deep processing (such as that based on semantics and meanings) results in a more durable memory trace. This theory suggests, then, that memory strength is continuously variable, as opposed to the earlier Atkinson-Shiffrin, or multi-store, memory model, which just involves a sequence of three discrete stages, from sensory to short-term to long-term memory.
The evidence suggests that memory retrieval is a more or less automatic process. Thus, although distraction or divided attention at the time of recall tends to slow down the retrieval process to some extent, it typically has little to no effect on the accuracy of retrieved memories. Distraction at the time of encoding, on the other hand, can severely impair subsequent retrieval success.
The efficiency of memory recall can be increased to some extent by making inferences from our personal stockpile of world knowledge, and by our use of schema (plural: schemata). A schema is an organized mental structure or framework of pre-conceived ideas about the world and how it works, which we can use to make realistic inferences and assumptions about how to interpret and process information. Thus, our everyday communication consists not just of words and their meanings, but also of what is left out and mutually understood (e.g. if someone says “it is 3 o’clock”, our knowledge of the world usually allows us to know automatically whether it is 3am or 3pm). Such schemata are also applied to recalled memories, so that we can often flesh out details of a memory from just a skeleton memory of a central event or object. However, the use of schemata may also lead to memory errors as assumed or expected associated events are added that did not actually occur.
There are three main types of recall:
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Several recent studies in the growing area of neuro-education have shown the value of the "testing effect" (or "retrieval effect"), where quizzes a short time after initial learning significantly improves subsequent retrieval of facts and ideas, as well as overall understanding of topics and the ability to solve related problems.
Testing helps protect against "proactive interference" (the familiar feeling of being overwhelmed by too much information), and the studies suggest that a quick test is much more effective than en extra hour of study or re-reading.
Free recall is the process in which a person is given a list of items to remember and then is asked to recall them in any order (hence the name “free”). This type of recall often displays evidence of either the primacy effect (when the person recalls items presented at the beginning of the list earlier and more often) or the recency effect (when the person recalls items presented at the end of the list earlier and more often), and also of the contiguity effect (the marked tendency for items from neighbouring positions in the list to be recalled successively).
Cued recall is the process in which a person is given a list of items to remember and is then tested with the use of cues or guides. When cues are provided to a person, they tend to remember items on the list that they did not originally recall without a cue, and which were thought to be lost to memory. This can also take the form of stimulus-response recall, as when words, pictures and numbers are presented together in a pair, and the resulting associations between the two items cues the recall of the second item in the pair.
Serial recall refers to our ability to recall items or events in the order in which they occurred, whether chronological events in our autobiographical memories, or the order of the different parts of a sentence (or phonemes in a word) in order to make sense of them. Serial recall in long-term memory appears to differ from serial recall in short-term memory, in that a sequence in long-term memory is represented in memory as a whole, rather than as a series of discrete items. Testing of serial recall by psychologists have yielded several general rules:
more recent events are more easily remembered in order (especially with auditory stimuli);
recall decreases as the length of the list or sequence increases;
there is a tendency to remember the correct items, but in the wrong order;
where errors are made, there is a tendency to respond with an item that resembles the original item in some way (e.g. “dog” instead of “fog”, or perhaps an item physically close to the original item);
repetition errors do occur, but they are relatively rare;
if an item is recalled earlier in the list than it should be, the missed item tends to be inserted immediately after it;
if an item from a previous trial is recalled in a current trial, it is likely to be recalled at its position from the original trial.
If we assume that the "purpose" of human memory is to use past events to guide future actions, then keeping a perfect and complete record of every past event is not necessarily a useful or efficient way of achieving this. So, in most people, some specific memories may be given up or converted into general knowledge (i.e. converted from episodic to semantic memories) as part of the ongoing recall/re-consolidation process, so that that we are able to generalize from experience.
It is also possible that false memories (or at least wrongly interpreted memories) may be created during recall, and carried forward thereafter. Research into false memory creation is particularly associated with Elizabeth Loftus' work in the 1970s. Among many other experiments in this area (see the side panel on the Psychogenic Amnesia page, for example), she showed how the precise wording of a question about memories (e.g. "the car hit" or "the car smashed into") can dramatically influence the recall and re-creation of memories, and can even permanently change those memories for future recalls - a phenomenon which is not lost on the legal profession. It is thought that it may even be possible, up to a point, to choose to forget, by blocking out unwanted memories during recall, a process achieved by frontal lobe activity, which inhibits the laying down or re-consolidation of a memory.
However, there is a rare condition called hyperthymesia (also known as hypermnesia or superior autobiographical memory) in which a few people show an extraordinary capacity to recall detailed specific events from a person’s personal past, without relying on practised mnemonic strategies. Although only a handful of cases of hyperthymesia have ever been definitively confirmed, some of these cases are quite startling, such as a California woman who could recall every day in complete detail from the age of 14 onwards, a young English girl with an IQ of 191 who had a perfect photographic memory spanning almost 18 years, and a Russian man known simply as "S." who was only able to forget anything by a deliberate act of will. One of the most famous cases, known as “A.J.”, described it as a burden rather than a gift, but others seem to be able to organize and compartmentalize their prodigious memories and do not appear to feel that their brains are "cluttered" with excess information. There is a good "60 Minutes" documentary on the subject at http://www.cbsnews.com/video/watch/?id=7166313n. Interestingly, recent research has shown that such individuals tend to have significantly larger than average temporal lobes and caudate nuclei, and many exhibit mild Obsessive Compulsive Disorder-like behaviour (the caudate nucleus is also associated with OCD).
Research into a cognitive disorder known as Korsakoff’s syndrome shows that the retrograde amnesia of sufferers follows a distinct temporal curve, in that the more remote the event in the past, the better it is preserved. This suggests that the more recent memories are not fully consolidated and therefore more vulnerable to loss, indicating that the process of consolidation may continue for much longer than initially thought, perhaps for many years. Korsakoff's syndrome, or Wernicke-Korsakoff syndrome, is a brain disorder caused by extensive thiamine deficiency, a form of malnutrition which can be precipitated by over-consumption of alcohol and alcoholic beverages compared to other foods. It main symptoms are anterograde amnesia (inability to form new memories and to learn new information or tasks) and retrograde amnesia (severe loss of existing memories), confabulation (invented memories, which are then taken as true due to gaps in memory), meagre content in conversation, lack of insight and apathy.
Individual Korsakoff's sufferers may exhibit wildly differing symptoms. In some cases, a patient may just continue "living in the past", convinced that their life and the world around them is unchanged since the onset of the condition (which may have been twenty or thirty years before). Others may adopt a constant, almost frenzied, fever of confabulation (see box at right), constantly inventing a series of new identities, often with detailed and convincing back-stories, in order to replace the reality which has been forgotten and lost.
Much about the disorder has been gleaned from a sufferer known as “Patient X”, who wrote an autobiography in 1979 and then developed the disease a short time later. Thus, his post-Korsakoff memories could be directly compared with the details in his written autobiography.
Korsakoff’s syndrome is caused by a deficiency of thiamine (vitamin B1), which is thought to cause damage to the thalamus and to the mammillary bodies of the hypothalamus (which receives many neural connections from the hippocampus), as well as generalized cerebral atrophy, neuronal loss and damage to neurons.
Typically, the retrograde amnesia of Korsakoff’s syndrome follows a distinct temporal curve: the more remote the event in the past, the better it is preserved and the sharper the recollection of it. This suggests that the more recent memories are not fully consolidated and therefore more vulnerable to loss, indicating that the process of consolidation may continue for much longer than initially thought, perhaps for many years.