Memory is the ability to recall information in the form of past events, ideas, and feelings. People have different types of memories, including short-term and long-term memory, and auditory and visual memory.
A brief history
The study of memory can be traced all the way back to Plato and Aristotle. Plato's metaphor for memory likened it to the impression made by a seal on wax and has been sustained throughout the history of Psychology. Aristotle's differentiation between memory and recollection closely parallels what we now refer to as short- and long-term memory. Although many other explanations of memory have been offered throughout history it would be another 1500 years before scientific methods were used in the study of memory.
The first use of the scientific method (i.e., rigorous experimental controls and statistical analyses) in the study of memory is credited to the German psychologist Hermann Ebbinghaus (1850–1909). Prior to the publication of his book On Memory in 1885, very little had been written about memory utilizing scientific methods and precise terminology. Ebbinghaus began by memorizing lists of unrelated words and later tested his memory for these words. He soon realized that some words were more familiar than others and were easier to recall. Consequently, he constructed lists of nonsense syllables, consisting of a consonant, a vowel, and a consonant. They are often referred to as CVCs, or trigrams (e.g., BIJ, VUN, PIB). Ebbinghaus wanted to know how much he could remember after various delay intervals, from 20 minutes to 30 days. It quickly became obvious that much of what he learned was quickly forgotten. But he also noticed that the more frequently he rehearsed (i.e., repeated) the list on day 1, the more quickly he could relearn it on day 2. He thus established a basic principle, namely that the time spent on learning affects the subsequent recall of the material. Ebbinghaus's approach has been referred to as a quantity-orientated approach. This perspective treats memory as a storehouse in which items are deposited and are later retrieved. It continues to be used to produce much of the data found in scientific journals today.
Ebbinghaus laid the foundation for the study of memory but he had little to say about the causes of forgetting. Georg Elias Muller (1850–1934) was the pioneer of what we now call the interference theory of forgetting. The interference theory, simplified, suggests that forgetting is not a consequence of material dying away but rather is due to other memories interfering at the time of retrieval. Two types of interference are retroactive interference and proactive interference. Retroactive interference refers to recently learned material interfering with the ability to remember previously stored information. Proactive interference refers to just the opposite phenomenon, when previously learned material interferes with the remembering of similar newly learned material.
Decay theory refers to the notion that the passage of time will cause memory traces to erode if they are not accessed from time to time. Generally speaking the longer the interval between learning and recall the less information will be recalled. The decay theory more effectively accounts for forgetting in the short term (e.g., remembering a phone number), whereas interference theory better accounts for long term forgetting.
The three-box model of memory
There are several existing models of memory but we will focus our attention on the three-box model because it is effective in organizing and accounting for many of the major research findings, and is the most widely used model you will encounter.
The three-box approach was originally termed the separate storage model by its developers, Atkinson and Shiffrin, in 1971. They proposed three separate but interacting systems that are used to gather, store, maintain, and retrieve information. The three systems are: sensory memory which acquires and holds incoming information for a second or two; short-term memory (STM) which holds information for approximately 30 seconds, unless an effort is made to keep it there longer; and long-term memory (LTM) which can hold information from a few minutes to decades.
Information from the environment enters the sensory memory store and remains there for half a second for visual stimuli and approximately two seconds for auditory stimuli. We also receive information from our sense of smell and from our sense of touch. These are referred to respectively as olfactory memory and tactile memory. Research in these latter two areas is relatively limited. The sensory memory store has been studied most extensively in regard to vision or iconic memory. A flash of lightening lasts only a fraction of a second but we can see the impression of the countryside for a moment after it occurs. This persisting impression is what is referred to as iconic sensory memory store.
We have all had the experience of performing a task while people are speaking in the background. In such situations you are not attending to the conversation but are instead focussed on the task at hand. Now suppose you hear your own name come up in the ongoing conversation. You suddenly become aware of it. This is an example of auditory sensory memory. Obviously, some portion of the speech stream is being stored in memory, otherwise you would not be able to recognize your name when it occurs.
One important thing to remember about both visual and auditory sensory memory is that the information is maintained for, at the very most, a few seconds before it is lost forever unless you pay attention to it and place it in your short term memory. Information that has been attended to is transferred from the sensory system to the short term memory (STM) store and remains there for thirty seconds or so unless the information is rehearsed, in which case it may remain for a longer period of time. STM is sometimes referred to as working memory or immediate memory because we have easy access to its contents. We have all experienced dialing the operator to obtain a phone number. Typically, we rehearse (i.e., repeat) the number to commit it to memory, hang up the receiver, and then dial the number. Should we need to use the same number later that day we most will likely have to look it up again. This illustrates the fact that information in STM will disappear unless we make a concerted effort to maintain it. Moreover, the capacity of STM is limited. If phone numbers were any longer than seven digits, dialing errors would increase substantially. Push button phones lowered the frequency of dialing errors because the time required to maintain the phone number in memory was reduced. With the old rotary phones, we used to have to wait until the disk returned to its original position before dialing the next number. With the higher digits (0, 9, 8, etc.) this could take a couple of seconds, thus putting an extra burden on our short term memory.
If information is transferred from STM to the LTM store it's retention may last from minutes to decades and in some cases its storage is permanent. It is here, in LTM, that information is organized and indexed. You know your name, what you did last Saturday night, how to ride a bicycle, and who the president of the United States is. These are all examples of information that resides in LTM. There are three different types of information in LTM: episodic memory; procedural memory; and semantic memory.
Episodic memory refers to the memory of events or activities (e.g., summer vacation or graduation day). What these memories have in common is that they refer to specific experiences. Some episodic memories are readily recalled while others may need prompting. Generally speaking the more significant the experience the more readily it can be recalled. Some insignificant events may need considerable prompting if they are to be remembered and some may not be remembered at all.
Procedural memory contains stored physical skills and behavioral operations. For example you may have learned how to roller-blade or skateboard. You have learned how to write a letter or an essay. Procedural memories are "how-to" memories. These memories are readily available even after years of disuse. The expression "It's like riding a bike, you never forget" captures this sense of permanency.
Semantic memory refers to general knowledge (e.g., the capital of France; what a zebra looks like). Semantic memory involves the meaning of words and objects. For example, most people know what an igloo is, but not as a result of having built one or being inside one.
WHAT GETS STORED AND WHAT GETS LOST? If we stop to consider the sheer volume of sensory input with which we are bombarded each day, it would be inconceivable that all of it passes into STM let alone LTM. What determines what gets saved and what gets lost? As mentioned earlier what we attend to in the sensory memory gets transferred to STM store. But how does this occur?
Encoding is the process by which information is added to our memory stores. Encoding changes the information we receive from our senses into a format that our brains can process and store. We do not encode into memory all that we see, hear, smell, touch, or feel. Sensory memory not only acts a holding tank from which items are selected for encoding and storage in STM, but it also acts as a filter, keeping out unimportant bits of information.
Information that is rehearsed in STM is accessible for immediate use, and can also be transferred to LTM. Other than acting as a retaining center for new information, the STM store also holds information for immediate use that has been recovered from the LTM store. It is for this reason that it is often referred to as working memory. When you spell a word the letters themselves and their appropriate arrangements enter the STM system as a result of having been retrieved from LTM.
When we make a deliberate effort to remember material we not only use rehearsal strategies, but other processes as well. Two of these processes are deep processing and mnemonics. Deep processing refers to the degree or "depth" to which we analyze or deal with the information. It can be contrasted with rote memorization, which can occur without our having any real understanding of the material. For example, it is possible (with considerable effort), to memorize passages of Latin without having any knowledge whatsoever of what the sentences mean. With deep processing however, the material to be remembered is not simply rehearsed but understood, elaborated upon, and thought about. It is its meaning that is encoded, not merely its initial form of expression. For example suppose you are trying to remember that an erythrocyte is a red blood cell. If you also appreciate that that the protein hemoglobin produces the red color, and the unique biconcave shape of the erythrocyte increases its surface area and thus facilitates the exchange of O2 and CO2 into or out of the cells of our bodies, you are using deep processing. On the other hand if you simply memorize the spelling of erythrocyte and repeat to yourself that it is a red blood cell you are using rehearsal.
To increase the chances of retrieving information from LTM, mnemonics may help. A mnemonics is a trick or device that we can use when encoding information that will help us retrieve it later on. Using our above example of erythrocytes, if you were to use the mnemonic "Red Engines Haul Oil to Boston" you could use that simple sentence to recall a fair amount of information about erythrocytes. In this example, the first letter of each word corresponds to some aspect of the to-be-remembered material (red blood cells, erythrocytes, hemoglobin, oxygen, and body) and the sentence describes what the red blood cells do—carry oxygen to the bodies cells. A good mnemonic is one that is simple, uses concrete nouns, and permits the formation of a clear visual image. If the mnemonic itself is difficult to remember, its usefulness is nullified.
BOOKS
Anderson, J. R. Learning and memory: An integrated approach. New York: Wiley, 1995.
Wade, C., and C. Tavris. Psychology, Sixth ed. New York: Addison Wesley Longham, Inc., 2000.
PERIODICALS
Koriat, A. Toward a psychology of memory accuracy." Annual Review of Psychology 51 (May 2001): 481-537.
