Stages of Memory - Encoding Storage and Retrieval
By Saul McLeod email icon published 2007
“Memory is the process of maintaining information over time.” (Matlin, 2005)
“Memory is the means by which we draw on our past experiences in order to use this information in the present’
(Sternberg, 1999).
Memory is the term given to the structures and processes involved in the storage and subsequent retrieval of information.
Memory is essential to all our lives. Without a memory of the past we cannot operate in the present or think about the
future. We would not be able to remember what we did yesterday, what we have done today or what we plan to do
tomorrow. Without memory we could not learn anything.
Memory is involved in processing vast amounts of information. This information takes many different forms, e.g. images,
sounds or meaning.
For psychologists the term memory covers three important aspects of information processing:
Stages of memory
1. Memory Encoding
When information comes into our memory system (from sensory input), it needs to be changed into a form that the system
can cope with, so that it can be stored. Think of this as similar to changing your money into a different currency when
you travel from one country to another. For example, a word which is seen (in a book) may be stored if it is changed
(encoded) into a sound or a meaning (i.e. semantic processing).
There are three main ways in which information can be encoded (changed):
1. Visual (picture)
2. Acoustic (sound)
3. Semantic (meaning)
For example, how do you remember a telephone number you have looked up in the phone book? If you can see it then
you are using visual coding, but if you are repeating it to yourself you are using acoustic coding (by sound).
Evidence suggests that this is the principle coding system in short term memory (STM) is acoustic coding. When a person
is presented with a list of numbers and letters, they will try to hold them in STM by rehearsing them (verbally). Rehearsal
is a verbal process regardless of whether the list of items is presented acoustically (someone reads them out), or visually
(on a sheet of paper).
The principle encoding system in long term memory (LTM) appears to be semantic coding (by meaning). However,
information in LTM can also be coded both visually and acoustically.
2. Memory Storage
This concerns the nature of memory stores, i.e. where the information is stored, how long the memory lasts for (duration),
how much can be stored at any time (capacity) and what kind of information is held. The way we store information
affects the way we retrieve it. There has been a significant amount of research regarding the differences between Short
Term Memory (STM) and Long Term Memory (LTM).
Most adults can store between 5 and 9 items in their short-term memory. Miller (1956) put this idea forward and he called
it the magic number 7. He though that short-term memory capacity was 7 (plus or minus 2) items because it only had a
certain number of “slots” in which items could be stored. However, Miller didn’t specify the amount of information that
can be held in each slot. Indeed, if we can “chunk” information together we can store a lot more information in our shortterm memory. In contrast the capacity of LTM is thought to be unlimited.
Information can only be stored for a brief duration in STM (0-30 seconds), but LTM can last a lifetime.
3. Memory Retrieval
This refers to getting information out storage. If we can’t remember something, it may be because we are unable to
retrieve it. When we are asked to retrieve something from memory, the differences between STM and LTM become very
clear.
STM is stored and retrieved sequentially. For example, if a group of participants are given a list of words to remember,
and then asked to recall the fourth word on the list, participants go through the list in the order they heard it in order to
retrieve the information.
LTM is stored and retrieved by association. This is why you can remember what you went upstairs for if you go back to
the room where you first thought about it.
Organizing information can help aid retrieval. You can organize information in sequences (such as alphabetically, by size
or by time). Imagine a patient being discharged from hospital whose treatment involved taking various pills at various
times, changing their dressing and doing exercises. If the doctor gives these instructions in the order which they must be
carried out throughout the day (i.e. in sequence of time), this will help the patient remember them.
Criticisms of Memory Experiments
A large part of the research on memory is based on experiments conducted in laboratories. Those who take part in the
experiments - the participants - are asked to perform tasks such as recalling lists of words and numbers. Both the setting the laboratory - and the tasks are a long way from everyday life. In many cases, the setting is artificial and the tasks fairly
meaningless. Does this matter?
Psychologists use the term ecological validity to refer to the extent to which the findings of research studies can be
generalized to other settings. An experiment has high ecological validity if its findings can be generalized, that is applied
or extended, to settings outside the laboratory.
It is often assumed that if an experiment is realistic or true-to-life, then there is a greater likelihood that its findings can be
generalized. If it is not realistic (if the laboratory setting and the tasks are artificial) then there is less likelihood that the
findings can be generalized. In this case, the experiment will have low ecological validity.
Many experiments designed to investigate memory have been criticized for having low ecological validity. First, the
laboratory is an artificial situation. People are removed from their normal social settings and asked to take part in a
psychological experiment. They are directed by an 'experimenter' and may be placed in the company of complete
strangers. For many people, this is a brand new experience, far removed from their everyday lives. Will this setting affect
their actions, will they behave normally?
Often, the tasks participants are asked to perform can appear artificial and meaningless. Few, if any, people would
attempt to memorize and recall a list of unconnected words in their daily lives. And it is not clear how tasks such as this
relate to the use of memory in everyday life. The artificiality of many experiments has led some researchers to question
whether their findings can be generalized to real life. As a result, many memory experiments have been criticized for
having low ecological validity.
References
Matlin, M. W. (2005). Cognition. Crawfordsville: John Wiley & Sons, Inc.
Miller, G. A. (1956). The magical number seven, plus or minus two: Some limits on our capacity for processing
information. Psychological Review, 63 (2): 81–97.
Sternberg, R. J. (1999). Cognitive psychology (2 nd ed.). Fort Worth, TX: Harcourt Brace College Publishers.
Forgetting
by Saul McLeod email icon published 2008
Why do we forget? There are two simple answers to this question.
First, the memory has disappeared - it is no longer available. Second, the memory is still stored in the memory system
but, for some reason, it cannot be retrieved.
These two answers summaries the main theories of forgetting developed by psychologists. The first answer is more likely
to be applied to forgetting in short term memory, the second to forgetting in long term memory.
Forgetting information from short term memory (STM) can be explained using the theories of trace decay and
displacement.
Forgetting from long term memory (LTM) can be explained using the theories of interference and lack of consolidation.
Trace Decay Theory of Forgetting
This explanation of forgetting in short term memory assumes that memories leave a trace in the brain. A trace is some
form of physical and/or chemical change in the nervous system. Trace decay theory states that forgetting occurs as a
result of the automatic decay or fading of the memory trace. Trace decay theory focuses on time and the limited duration
of short term memory.
This theory suggests short term memory can only hold information for between 15 and 30 seconds unless it is rehearsed.
After this time the information / trace decays and fades away.
No one disputes the fact that memory tends to get worse the longer the delay between learning and recall, but there is
disagreement about the explanation for this effect.
According to the trace decay theory of forgetting, the events between learning and recall have no affected whatsoever on
recall. It is the length of time the information has to be retained that is important. The longer the time, the more the
memory trace decays and as a consequence more information is forgotten.
There are a number of methodological problems confronting researchers trying to investigate the trace decay theory. One
of the major problems is controlling for the events that occur between learning and recall. Clearly, in any real-life
situation, the time between learning something and recalling it will be filled with all kinds of different events. This makes
it very difficult to be sure that any forgetting which takes place is the result of decay rather than a consequence of the
intervening events.
Support for the idea that forgetting from short-term memory might be the result of decay over time came from research
carried out by Brown (1958) in the United Kingdom, and Peterson and Peterson (1959) in the United States. The
technique they developed has become known as the Brown-Peterson task.
Evaluation
There is very little direct support for decay theory as an explanation for the loss of information from short-term and longterm memory. One of the problems with decay theory is that it is more or less impossible to test it. In practice, it is not
possible to create a situation in which there is a blank period of time between presentation of material and recall. Having
presented information participants will rehearse it. If you prevent rehearsal by introducing a distracter task, it results in
interference.
Decay theory has difficulty explaining the observation that many people can remember events that happened several years
previously with great clarity, even though they haven't thought about them during the intervening period. If our memories
gradually decayed over time, then people should not have clear memories of distant events which have lain dormant for
several years. However, there is evidence to suggest that information is lost from sensory memory through the process of
decay (Sperling, 1960).
Displacement from STM
Displacement seeks to explain forgetting in short term memory, and suggests it’s due to a lack of availability.
Displacement theory provides a very simple explanation of forgetting. Because of its limited capacity, suggested by
Miller to be 7+/- 2 items, STM can only hold small amounts of information.
When STM is 'full', new information displaces or 'pushes out’ old information and takes its place. The old information
which is displaced is forgotten in STM.
It was also assumed that the information that had been in the short-term store for the longest was the first to be displaced
by new information, similar to the way in which boxes might fail off the end of a conveyor belt - as new boxes are put on
one end, the boxes which have been on the conveyor belt the longest drop off the end.
Support for the view that displacement was responsible for the loss of information from short-term memory came from
studies using the 'free-recall' method.
A typical study would use the following procedure: participants listen to a list of words read out a steady rate, usually two
seconds per word; they are then asked to recall as many of words as possible. They are free to recall the words in any
order, hence the term 'free recall'.
The findings from studies using free recall are fairly reliable and they produce similar results on each occasion. If you
take each item in the list and calculate the probability of participants recalling it (by averaging recall of the word over all
participants) and plot this against the item's position in the list, it results in the serial position curve (Figure 1).
serial position effect
Fig 1. Simplified representation of the serial position curve for immediate recall
Good recall of items at the beginning of the list is referred to as the primacy effect and good recall if items at the end of
the list are referred to as the recency effect. The displacement theory of forgetting from short-term memory can explain
the recency effect quite easily. The last few words that were presented in the list have not yet been displaced from shortterm memory and so are available for recall.
The primacy effect can be explained using Atkinson & Shiffrin's (1968) multi-store model which proposes that
information is transferred into long-term memory by means of rehearsal.
The first words in the list are rehearsed more frequently because at the time they are presented they do not have to
compete with other words for the limited capacity of the short-term store. This means that words early in the list are more
likely to be transferred to long-term memory.
So the primacy effect reflects items that are available for recall from long-term memory. However, words in the middle of
the list used to be in short term memory until they were pushed out - or displaced by the words at the end of the list.
Evaluation
Displacement theory provided a good account of how forgetting might take place in Atkinson & Shiffrin's (1968) model
of short-term memory. However, it became clear that the short-term memory store is much more complex than proposed
in Atkinson and Shiffrin's model (re: working memory).
Murdock’s (1962) serial position experiment supports the idea of forgetting due to displacement from short term memory,
although it could be due to decay. Forgetting from short term memory can occur due to displacement or due to decay, but
it is often very difficult to tell which one it is.
Interference Theory
If you had asked psychologists during the 1930s, 1940s, or 1950s what caused forgetting you would probably have
received the answer "Interference".
It was assumed that memory can be disrupted or interfered with by what we have previously learned or by what we will
learn in the future. This idea suggests that information in long term memory may become confused or combined with
other information during encoding thus distorting or disrupting memories.
Interference theory states that forgetting occurs because memories interfere with and disrupts one another, in other words
forgetting occurs because of interference from other memories (Baddeley, 1999). There are two ways in which
interference can cause forgetting:
1. Proactive interference (pro=forward) occurs when you cannot learn a new task because of an old task that had been
learnt. When what we already know interferes with what we are currently learning – where old memories disrupt new
memories.
2. Retroactive interference (retro=backward) occurs when you forget a previously learnt task due to the learning of a new
task. In other words, later learning interferes with earlier learning - where new memories disrupt old memories.
Proactive and retroactive Interference is thought to be more likely to occur where the memories are similar, for example:
confusing old and new telephone numbers. Chandler (1989) stated that students who study similar subjects at the same
time often experience interference.
Previous learning can sometimes interfere with new learning (e.g. difficulties we have with foreign currency when
travelling abroad). Also new learning can sometimes cause confusion with previous learning. (Starting French may affect
our memory of previously learned Spanish vocabulary). In the short term memory interference can occur in the form of
distractions so that we don’t get the chance to process the information properly in the first place. (e.g. someone using a
loud drill just outside the door of the classroom.)
Key study: Postman (1960)
Aim: To investigate how retroactive interference affects learning. In other words, to investigate whether information you
have recently received interferes with the ability to recall something you learned earlier.
Method: A lab experiment was used. Participants were split into two groups. Both groups had to remember a list of paired
words – e.g. cat - tree, jelly - moss, book - tractor. The experimental group also had to learn another list of words where
the second paired word if different – e.g. cat – glass, jelly- time, book – revolver. The control group were not given the
second list. All participants were asked to recall the words on the first list.
Results: The recall of the control group was more accurate than that of the experimental group.
Conclusion: This suggests that learning items in the second list interfered with participants’ ability to recall the list. This
is an example of retroactive interference.
Evaluation
Although proactive and retroactive interference are reliable and robust effects, there are a number of problems with
interference theory as an explanation of forgetting.
First, interference theory tells us little about the cognitive processes involved in forgetting. Secondly, the majority of
research into the role of interference in forgetting has been carried out in a laboratory using lists of words, a situation
which is likely to occur fairly infrequently in everyday life (i.e. low ecological validity). As a result, it may not be
possible to generalize from the findings.
Baddeley (1990) states that the tasks given to subjects are too close to each other and, in real life; these kinds of events are
more spaced out. Nevertheless, recent research has attempted to address this by investigating 'real-life' events and has
provided support for interference theory. However, there is no doubt that interference plays a role in forgetting, but how
much forgetting can be attributed to interference remains unclear (Anderson, 2000).
Lack of consolidation
The previous accounts of forgetting have focused primarily on psychological evidence, but memory also relies on
biological processes. For example, we can define a memory trace as:
'some permanent alteration of the brain substrate in order to represent some aspect of a past experience'.
When we take in new information, a certain amount of time is necessary for changes to the nervous system to take place –
the consolidation process – so that it is properly recorded. During this period information is moved from short term
memory to the more permanent long term memory.
The brain consists of a vast number of cells called neurons, connected to each other by synapses. Synapses enable
chemicals to be passed from one neuron to another. These chemicals, called neurotransmitters, can either inhibit or
stimulate the performance of neurons.
So if you can imagine a network of neurons all connected via synapses, there will be a pattern of stimulation and
inhibition. It has been suggested that this pattern of inhibition and stimulation can be used as a basis for storing
information. This process of modifying neurons in order form new permanent memories is referred to as consolidation
(Parkin, 1993).
There is evidence that the consolidation process is impaired if there is damage to the hippocampus (a region of the brain).
In 1953, HM had brain surgery to treat his epilepsy, which had become extremely severe. The surgery removed parts of
his brain and destroyed the hippocampus, and although it relieved his epilepsy, it left him with a range of memory
problems. Although his STM functioned well, he was unable to process information into LTM.
The main problem experienced by HM is his inability to remember and learn new things. This inability to form new
memories is referred to as anterograde amnesia. However, of interest in our understanding of the duration of the process
of consolidation is HM's memory for events before his surgery. In general, his memory for events before the surgery
remains intact, but he does have some memory loss for events which occurred in the two years leading up to surgery.
Pinel (1993) suggests that this challenges Hebb's (1949) idea that the process of consolidation takes approximately 30
minutes. The fact that HM's memory is disrupted for the two-year period leading up to the surgery indicates that the
process of consolidation continues for a number of years.
Finally, aging can also impair our ability to consolidate information.
Evaluation
The research into the processes involved in consolidation reminds us that memory relies on biological processes, although
the exact manner by which neurons are altered during the formation of new memories has not yet been fully explained.
However, there is no doubt that investigating the role of neurons and neurotransmitters will provide new and important
insights into memory and forgetting.
Retrieval Failure Theory
Retrieval failure is where the information is in long term memory, but cannot be accessed. Such information is said to be
available (i.e. it is still stored) but not accessible (i.e. it cannot be retrieved). It cannot be accessed because the retrieval
cues are not present.
When we store a new memory we also store information about the situation and these are known as retrieval cues. When
we come into the same situation again, these retrieval cues can trigger the memory of the situation. Retrieval cues can be:
External / Context - in the environment, e.g. smell, place etc.
Internal / State- inside of us, e.g. physical, emotional, mood, drunk etc.
There is considerable evidence that information is more likely to be retrieved from long-term memory if appropriate
retrieval cues are present. This evidence comes from both laboratory experiments and everyday experience. A retrieval
cue is a hint or clue that can help retrieval.
Tulving (1974) argued that information would be more readily retrieved if the cues present when the information was
encoded were also present when its retrieval is required. For example, if you proposed to your partner when a certain song
was playing on the radio, you will be more likely to remember the details of the proposal when you hear the same song
again. The song is a retrieval cue - it was present when the information was encoded and retrieved.
Tulving suggested that information about the physical surroundings (external context) and about the physical or
psychological state of the learner (internal context) is stored at the same time as information is learned. Reinstating the
state or context makes recall easier by providing relevant information, while retrieval failure occurs when appropriate cues
are not present. For example, when we are in a different context (i.e. situation) or state.
Context (external) Cues
Retrieval cues may be based on context-the setting or situation in which information is encoded and retrieved. Examples
include a particular room, driving along a motorway, a certain group of people, a rainy day and so on.
Context also refers to the way information is presented. For example, words may be printed, spoken or sung, they may be
presented in meaningful groups - in categories such as lists of animals or furniture - or as a random collection without any
link between them. Evidence indicates that retrieval is more likely when the context at encoding matches the context at
retrieval.
You may have experienced the effect of context on memory if you have ever visited a place where you once lived (or an
old school). Often such as visit helps people recall lots of experiences about the time they spent there which they did not
realize were stored in their memory.
A number of experiments have indicated the importance of context-based cues for retrieval. An experiment conducted by
Tulving and Pearlstone (1966) asked participants to learn lists of words belonging to different categories, for example
names of animals, clothing and sports.
Participants were then asked to recall the words. Those who were given the category names recalled substantially more
words than those who were not. The categories provided a context, and naming the categories provided retrieval cues.
Tulving and Pearlstone argued that cue-dependent forgetting explains the difference between the two groups of
participants. Those who recalled fewer words lacked appropriate retrieval cues.
An interesting experiment conducted by Baddeley (1975) indicates the importance of setting for retrieval. Baddeley
(1975) asked deep-sea divers to memorize a list of words. One group did this on the beach and the other group
underwater. When they were asked to remember the words half of the beach learners remained on the beach, the rest had
to recall underwater.
Half of the underwater group remained there and the others had to recall on the beach. The results show that those who
had recalled in the same environment (i.e. context) which that had learned recalled 40% more words than those recalling
in a different environment. This suggests that the retrieval of information is improved if it occurs in the context in which it
was learned.
State (internal) Dependent Cues
The basic idea behind state-dependent retrieval is that memory will be best when a person's physical or psychological
state is similar at encoding and retrieval. For example, if someone tells you a joke on Saturday night after a few drinks,
you'll be more likely to remember it when you're in a similar state - at a later date after a few more drinks. Stone cold
sober on Monday morning, you'll be more likely to forget the joke.
State Retrieval clues may be based on state-the physical or psychological state of the person when information is encoded
and retrieved. For example, a person may be alert, tired, happy, sad, drunk or sober when the information was encoded.
They will be more likely to retrieve the information when they are in a similar state.
Tulving and Pearlstone’s (1966) study involved external cues (e.g. presenting category names). However, cue-dependent
forgetting has also been shown with internal cues (e.g. mood state). Information about current mood state is often stored
in the memory trace, and there is more forgetting if the mood state at the time of retrieval is different. The notion that
there should be less forgetting when the mood state at learning and at retrieval is the same is generally known as moodstate-dependent memory.
A study by Goodwin et al. (1969) investigated the effect of alcohol on state-dependent retrieval. They found that when
people encoded information when drunk, they were more likely to recall it in the same state. For example, when they hid
money and alcohol when drunk, they were unlikely to find them when sober. However, when they were drunk again, they
often discovered the hiding place. Other studies found similar state-dependent effects when participants were given drugs
such as marijuana.
People tend to remember material better when there is a match between their mood at learning and at retrieval. The effects
are stronger when the participants are in a positive mood than a negative mood. They are also greater when people try to
remember events having personal relevance.
Evaluation
According to retrieval-failure theory, forgetting occurs when information is available in LTM but is not accessible.
Accessibility depends in large part on retrieval cues. Forgetting is greatest when context and state are very different at
encoding and retrieval. In this situation, retrieval cues are absent and the likely result is cue-dependent forgetting.
There is considerable evidence to support this theory of forgetting from laboratory experiments. The ecological validity of
these experiments can be questioned, but their findings are supported by evidence from outside the laboratory. For
example, many people say they can't remember much about their childhood or their school days. But returning to the
house in which they spent their childhood or attending a school reunion often provides retrieval cues which trigger a flood
of memories.
References
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