MEMORY AND LEARNING

MEMORY AND LEARNING Learning is a relatively permanent change in behaviour that marks an increase in knowledge, skills, or understanding thanks to recorded memories. A memory is the fruit of this learning process, the concrete trace of it that is left in your neural networks. Human memory is fundamentally associative. You can remember a new piece of information better if you can associate it with previously acquired knowledge that is already firmly anchored in your memory. And the more meaningful the association is to you personally, the more effectively it will help you to remember. So taking the time to choose a meaningful association can pay off in the long run. Also, contrary to the image that many people have of memory as a vast collection of archived data, most of our memories are actually reconstructions. They are not stored in our brains like books on library shelves. Whenever we want to remember something, we have to reconstruct it from elements scattered throughout various areas of our brains. Thus, scientists today view remembering not as a simple retrieval of fixed records, but rather as an ongoing process of reclassification resulting from continous changes in our neural pathways and parallel processing of information in our brains. To illustrate these two fundamental properties of memory, suppose that a school class has visited a museum of Egyptian art on a rainy day. Ten years later, the teacher, now retired, reads a history book that mentions the name of a mummy that was on display in that museum. The mummy’s name reminds the teacher of that class trip ten years ago. Then, by association, the teacher remembers some students from that class whom he had not even thought about since then. He can even remember how fascinated they were with the mummy, and some of the questions they asked him about it. In short, he has formed associative memories: one thing reminds him of another, which reminds him of yet another, and so on.   Now imagine that one of the students had had a very bad time on that trip, because she was interested in a boy in that class, and he was ignoring her. Ten years later, as she is taking off her wet raincoat, she too remembers that day. Except that now she remembers herself as holding that boy’s hand while they listened, enraptured, to the teacher’s explanations. Why the change? Because she ended up marrying that boy, and they are very happy together, so her present happiness has embellished her memory of the past. Thus, memories are not like snapshots that are always the same every time you take them out to look at them. They are also something that you reconstruct. But memory has other characteristics than can make learning easier once you understand them.

	A person’s short-term memory capacity is generally measured by the number of items they can retain when each is presented to them only once. on average, people have a short-term memory capacity of 7 items, plus or minus 2. An item can be defined as a “piece” of information. Consequently, one way to increase the storage capacity of short-term memory might be to increase the size of these pieces of information through a more effective encoding strategy, such as grouping. Here are two phenomena suggesting that there are in fact two distinct systems for short-term and long-term memory. First of all, our abilities to retain items at the start and end of a list are not equally affected by distractions. If a distraction occurs, we tend to forget the items at the end of the list (i.e., those stored in short-term memory) while remembering the ones at the start of it. In technical terms, the recency effect is attributable to short-term memory, while the primacy effect is attributable to long-term memory. Second, people with anterograde amnesia cannot form new long-term memories, but their short-term memory remains intact.		SENSORY, SHORT-TERM AND LONG-TERM MEMORY In the 1960s, the distinction among various types of memory according to their duration was the subject of passionate debates. Some scientists thought that the most elegant way to account for the data available at the time was to conceptualize memory as a single system of variable duration. But bit by bit, evidence accumulated that suggested the existence of at least three distinct memory systems. Though the mechanisms of these three systems differ, they do flow naturally from one into the other and can be regarded as three necessary steps in forming a lasting memory. According to this now generally accepted model, the stimuli detected by our senses can be either ignored, in which case they disappear almost instantaneously, or perceived, in which case they enter our sensory memory. Sensory memory does not require any conscious attention; as information is perceived, it is stored in sensory memory automatically. But sensory memory is essential, because it is what gives us the effect of unity of an object as our eyes jump from point to point on its surface to examine its details, for example. For instance, if the object in your sensory memory is a red octagon, you may or may not pay attention to it. If you do pay attention, you recognize that it is a stop sign. once you have paid such attention to a piece of information, it can pass on to your short-term memory. Your short-term memory lets you record limited amounts of information for periods of less than one minute. With an active effort, you can keep a piece of information in short-term memory for longer–for example, by repeating a telephone number until you have finished dialing it. Otherwise, the memory will disappear in less than a minute. Keeping an item in short-term memory for a certain amount of time lets you eventually transfer it to long-term memory for more permanent storage. This process is facilitated by the mental work of repeating the information, which is why the ｅxpression “working memory” is increasingly used as a synonym for short-term memory. But such repetition seems to be a less effective strategy for consolidating a memory than the technique of giving it a meaning by associating it with previously acquired knowledge. Once the piece of information has been stored in your long-term memory, it can remain there for a very long time, and sometimes even for the rest of your life. There are, however, several factors that can make these memories hard to retrieve. These factors include how long it has been since the event stored in your memory occurred, how long it has been since the last time you remembered it, how well you have integrated it with your own knowledge, whether it is unique, whether it resembles a current event, and so on. Many experiments still need to be conducted to assess the influence of each of these factors more closely. Nevertheless, we are beginning to gain a better understanding of the underlying systems necessary for each of these three types of memory to work properly.

	Implicit memory is the kind of latent memory that we are not aware of, but that nevertheless influences our behaviour. All advertising is based on the principle of implicit memory. We are so bombarded by advertising messages that we think we no longer even see them and hence do not remember them. But experiments have shown that when we go into a store and have to choose among products with equivalent characteristics, we tend to buy the one that has been the subject of an advertising campaign, and we cannot even say why! The same principle would also explain what is happening when you have a brilliant idea that seems to have sprung straight out of your own imagination, then realize later on that you actually read about it while browsing through last Saturday’s newspaper.   SENSORY, SHORT-TERM AND LONG-TERM MEMORY Sensory memory is the memory that results from our perceptions automatically and generally disappears in less than a second. It includes two sub-systems: iconic memory of visual perceptions and echoic memory of auditory perceptions. Short-term memory depends on the attention paid to the elements of sensory memory. Short-term memory lets you retain a piece of information for less than a minute and retrieve it during this time. one typical example of its use is the task of repeating a list of items that has just been read to you, in their original order. In general, you can retain 5 to 9 items (or, as it is often put, 7±2 items) in short-term memory. Working memory is a more recent extension of the concept of short-term memory. As techniques for studying memory have become more refined, it has become increasingly apparent that the original conception of short-term memory as a mere temporary receptacle for long-term memory is too simplistic. In fact, it is becoming increasingly clear that there is no strict line of demarcation between memories and thoughts. In order to test some hypotheses that may provide a better understanding of this complex phenomenon, the concept of working memory has therefore been advanced. Working memory is used to perform cognitive processes on the items that are temporarily stored in it. It would therefore be heavily involved in processes that require reasoning, such as reading, or writing, or performing computations. one typical example of the use of working memory is the task of repeating a list of items that has just been read to you, but in the reverse of their original order. Another good example is the task of simultaneous interpretation, where the interpreter must store information in one language while orally translating it into another. Working memory appears to be composed of several independent systems, which would imply that we are not aware of all the information that is stored in it at any given time. For example, when you drive a car, you are performing several complex tasks simultaneously. It is unlikely that all of the various types of information involved are being handled by a single short-term memory system. Long-term memory includes both our memory of recent facts, which is often quite fragile, as well as our memory of older facts, which has become more consolidated. Long-term memory consists of three main processes that take place consecutively: encoding, storage, and retrieval (recall) of information. The purpose of encoding is to assign a meaning to the information to be memorized. For example, you might encode the word "lemon" as “fruit, roundish, yellow”. If you could not recall the word “lemon” spontaneously, then invoking one of the indexes that you used to encode it (such as “fruit”) should help you to retrieve it. How effectively you can retrieve information depends on how deeply you have encoded it, and hence on how well you have organized it in your memory. The process of encoding refers not only to the information being memorized, but also to its environmental, cognitive, and emotional context. Also, using mnemonic devices to associate ideas and images helps us to create links that facilitate encoding. (One classic example is the acrostic Every Good Boy Deserves Favour, for the musical notes on the lines of the treble clef.) But even when information has been well encoded, it can still be forgotten. Storage can be regarded as the active process of consolidation that makes memories less vulnerable to being forgotten. It is this consolidation that differentiates memories of recent facts from memories of older ones. The latter have been associated with a larger amount of pre-existing knowledge. Sleep, and in particular the rapid-eye-movement (REM) phase of sleep, along with reviewing (such as studying for exams) play a large role in consolidation. Lastly, retrieval (recall) of memories, whether voluntary or not, involves active mechanisms that make use of encoding indexes. In this process, information is temporarily copied from long-term memory into working memory, so that it can be used there. The more a memory has been encoded, elaborated, organized, and structured, the easier it will be to retrieve. Thus, we see that forgetting can be caused by failures at any of these stages: poor encoding, insufficient consolidation, or difficulties in retrieval. Retrieval of information encoded in long-term memory is traditionally divided into two categories: recall and recognition. Recall involves actively reconstructing the information, whereas recognition only requires a decision as to whether one thing among others has been encountered before. Recall is more difficult, because it requires the activation of all the neurons involved in the memory in question. In contrast, in recognition, even if a part of an object initially activates only a part of the neural network concerned, that may then suffice to activate the entire network.           Semantic memory can be regarded as the residue of experiences stored in episodic memory. Semantic memory homes in on common features of various episodes and extracts them from their context. A gradual transition takes place from episodic to semantic memory. In this process, episodic memory reduces its sensitivity to particular events so that the information about them can be generalized. Conversely, our understanding of our personal experiences is necessarily due to the concepts and knowledge stored in our semantic memory. Thus, we see that these two types of memory are not isolated entities, but rather interact with each other constantly. In Alzheimer’s disease, patients quickly develop difficulty in retrieving individual words and general knowledge. Studies have shown that in tasks such as describing and naming items, these patients display a loss of knowledge of the specific characteristics of semantic categories. Initially, they lose the ability to distinguish fine categories, such as species of animals or types of objects. But over time, this lack of discrimination extends to broader, more general categories. At first, if you show such patients a spaniel, they may say, “that is a dog”. Later, they may just say “that is an animal”. DIFFERENT TYPES OF LONG-TERM MEMORY As the diagram below shows, long-term memory can be divided into explicit and implicit memory, and implicit memory can in turn be divided into various subtypes. But always bear in mind that in the actual workings of human memory, these various subsystems are interacting all the time. The interactions between episodic and semantic memory-two distinct forms of explicit memory-may offer the best example (see sidebar). Episodic memory (sometimes called autobiographical memory) lets you remember events that you personally experienced at a specific time and place. It includes memories such as the meal you ate last night, or the name of an old classmate, or the date of some important public event. The most distinctive feature of episodic memory is that you see yourself as an actor in the events you remember. You therefore memorize not only the events themselves, but also the entire context surrounding them. Episodic memory is the kind most often affected by various forms of amnesia. Also, the emotional charge that you experience at the time of the events conditions the quality of your memorization of the episode. Semantic memory is the system that you use to store your knowledge of the world. It is a knowledge base that we all have and much of which we can access quickly and effortlessly. It includes our memory of the meanings of words–the kind of memory that lets us recall not only the names of the world’s great capitals, but also social customs, the functions of things, and their colour and odour. Semantic memory also includes our memory of the rules and concepts that let us construct a mental representation of the world without any immediate perceptions. Its content is thus abstract and relational and is associated with the meaning of verbal symbols. Semantic memory is independent of the spatial/temporal context in which it was acquired. Since it is a form of reference memory that contains information accumulated repeatedly throughout our lifetimes, semantic memory is usually spared when people suffer from amnesia, but it can be affected by some forms of dementia (see sidebar). http://thebrain.mcgill.ca/flash/a/a_07/a_07_p/a_07_p_tra/a_07_p_tra.html#2		DIFFERENT TYPES OF LONG-TERM MEMORY From a clinical and physiological standpoint, many observations suggest that there may be various sub-categories of long-term memory. For example, certain kinds of amnesia affect certain kinds of memories, but not others. Similarly, researchers have found that various brain structures specialize in processing various kinds of memories. One of the most fundamental of these distinctions is between declarative and non-declarative memory, based on whether the memory’s content can be expressed verbally. Traditionally, most memory studies have focused on explicit memory, which involves the subjects' conscious recollection of things and facts. For instance, subjects might be asked to memorize a given set of items (a list of words, a group of pictures, etc.) and then recall them verbally. Also, things that are encoded in implicit memory can be recalled automatically, without the conscious effort needed to recall things from explicit memory. Perhaps the best known of the various types of implicit memory is procedural memory, which enables people to acquire motor skills and gradually improve them. Procedural memory is unconscious, not in the Freudian sense of suppressed memories, but because it is composed of automatic sensorimotor behaviours that are so deeply embedded that we are no longer aware of them. Patients with profound amnesia often retain their procedural memory, which argues for a system of separate neural pathways. Implicit memory is also where many of our conditioned reflexes and conditioned emotional responses are stored. The associative learning that constitutes the basis for these forms of memory is a very old process, phylogenetically speaking, and can take place without the intervention of the conscious mind. We form implicit memories without being aware that we are doing so. Hence, scientists who study such memories must often try to uncover them by indirect methods, such as "priming". In priming, researchers try to increase the speed or accuracy with which their subjects make a decision by first exposing them to information that relates to the same context, but without the subjects' having any other particular reason to retrieve the piece of information concerned. For example, subjects will take less time to decide that the string of letters "doctor" is a word if they have first been shown the word "nurse" than if they have first been shown an irrelevant word, such as "north", or a nonsense word, such as "nuber". Like implicit memory, explicit memory can be divided into subtypes - most often, episodic and semantic memory.