learning event, the long term memory for the event is not instantaneously formed. Rather,
information regarding the event is slowly assimilated into long-term storage over time, a process
referred to as memory consolidation, until it reaches a relatively permanent state.
During the consolidation period, the memory can be modulated. In particular, it appears that
emotional arousal following the learning event influences the strength of the subsequent memory
for that event. Greater emotional arousal following a learning event enhances a person's retention
of that event. Experiments have shown that administration of stress hormones to individuals
immediately after they learn something enhances their retention when they are tested two weeks
later.
The amygdale, especially the basolateral nuclei, are involved in mediating the effects of
emotional arousal on the strength of the memory for the event. There were experiments
conducted by James McGaugh on animals in a special laboratories. These laboratories have
trained animals on a variety of learning tasks and found that drugs injected into the amygdala
after training affect the animals' subsequent retention of the task. These tasks include basic
Pavlovian tasks such as inhibitory avoidance, where a rat learns to associate a mild footshock
with a particular compartment of an apparatus, and more complex tasks such as spatial or cued
water maze, where a rat learns to swim to a platform to escape the water. If a drug that activates
the amygdale is injected into the amygdale, the animals had better memory for the training in the
task. If a drug that inactivates the amygdale is injected, the animals had impaired memory for the
task.
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Despite the importance of the amygdale in modulating memory consolidation, however, learning
can occur without it, though such learning appears to be impaired, as in fear conditioning
impairments following amygdale damage.
Evidence from work with humans indicates that the amygdale plays a similar role. Amygdale
activity at the time of encoding information correlates with retention for that information.
However, this correlation depends on the relative "emotionalness" of the information. More
emotionally-arousing information increases amygdalar activity, and that activity correlates with
retention.
Hippocampus
Psychologists and neuroscientists dispute the precise role of the hippocampus, but, in general,
agree that it has an essential role in the formation of new memories about experienced events
(episodic or autobiographical memory). Some researchers prefer to consider the hippocampus as
part of a larger medial temporal lobe memory system responsible for general declarative memory
(memories that can be explicitly verbalized — these would include, for example, memory for
facts in addition to episodic memory).
Some evidence supports the idea that, although these forms of memory often last a lifetime, the
hippocampus ceases to play a crucial role in the retention of the memory after a period of
consolidation. Damage to the hippocampus usually results in profound difficulties in forming
new memories (anterograde amnesia), and normally also affects access to memories prior to the
damage (retrograde amnesia). Although the retrograde effect normally extends some years prior
to the brain damage, in some cases older memories remain - this sparing of older memories leads
to the idea that consolidation over time involves the transfer of memories out of the hippocampus
to other parts of the brain. However, experimentation has difficulties in testing the sparing of
older memories; and, in some cases of retrograde amnesia, the sparing appears to affect memories
formed decades before the damage to the hippocampus occurred, so its role in maintaining these
older memories remains controversial.
Damage to the hippocampus does not affect some aspects of memory, such as the ability to learn
new skills (playing a musical instrument, for example), suggesting that such abilities depend on a
different type of memory (procedural memory) and different brain regions. And there is some
evidence to suggest that patient HM (who had his medial temporal lobes removed bilaterally as a
treatment for epilepsy) can form new semantic memories.
Types of Memory
In the following section we will discuss the three different types of memory and their respective
characteristics: Sensory Memory, Short Term (STM) or Working Memory and Long Term Memory
(LTM).
Sensory Memory
This type of memory has the shortest duration time, only 0.5 to 2.0 seconds. Roughly, Sensory
Memory can be subdivided into two kinds: iconic and echoic memory. The first is concerned with
visual input, the latter with auditory input. (It should be noted, though, that according to the Atkinson
and Shiffrin model of memory, only iconic memory is equal to sensory memory. The addition of echoic
memory to the level of sensory memory is due to research done by Darwin and others (1972).) Let us
consider the following intuitive example for iconic memory: probably we all know the phenomenon
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that it seems possible to draw lines, figures or names with lighted sparklers by moving the sparkler fast
enough in a dark environment. Physically, however, there are no such things as lines of light. So how
come we can nevertheless see such figures? This is due to iconic memory. Roughly speaking, we can
think of this subtype of memory as a kind of photographic memory, but one which only lasts for a very
short time. The image of the light of a sparkler remains in our memory (persistence of vision) and thus
makes it seem to us like the light would leave lines in the dark. The same effect occurs, e.g., if we
watch a sprinkler and we think that we can see a ring of water drops. As for echoic memory, as the
name already suggests, it is meant to apply to auditory input. Here the persistence time is a little longer
as with iconic memory (up to 4 seconds). At the level of sensory memory no manipulation of the
incoming information occurs, it is simply transferred to, e.g., short term memory (at least the
information that is somehow important at the time of perception is transferred).
Short Term Memory
The term "short term memory" stems from the modal model approach to memory by Atkinson and
Shiffrin. In more modern approaches the idea of short term memory has been further investigated and
there seems to be evidence that also short term memory consists of several separated, but of course
closely related, subparts. Baddeley (2000) introduced the nowadays most often used term "working
memory". We will first look at the modal model approach and then go on to the concept of working
memory.
Short Term Memory
As the name suggests, information is stored in short term memory for a rather short period of time
(15-20 seconds). If we look up a phone number in the phone book and memorize it long enough until
we dialed that number, it is stored in short term memory. (Unless we want to remember that phone
number for a longer period of time, it will most probably not be stored in long term memory.) Now we
know how long information can be stored in short term memory, but what about the question about
how much can be stored? George Miller in his seminal paper (1956) proposed "the magical number
seven, plus minus two". He showed that between 5 and 9 items can usually be stored in short term
memory at a time. The term "item" might strike one as a little vague, all of the following are considered
items: single digits or letters, whole words or even sentences, and the like. It has been shown by
experiments also done by Miller that chunking is a useful method to memorize more than just single
items. Gobet et al. defined a chunk as "a collection of elements that are strongly associated with one
another but are weakly associated with other chunks" (p. 157 in Goldstein). A famous experiment was
conducted by Chase and Simon (1973) with amateur and experienced chess players. When asked to
remember certain arrangements of chess pieces on the board, the experts performed significantly better
that the amateurs. However, if the pieces were arranged arbitrarily, i.e. not corresponding to possible
game situations, both the experts and the amateurs performed equally bad. This shows that chunking
(as done by experienced chess players) enhances the performance in such memory tasks.
Problems with the Modal Model Approach: According to the memory-model proposed by
Atkinson and Shiffrin, all information has to pass the STM in order to be stored in LTM. However,
cases have been reported where patients can form long term memories even though their STM-abilities
are severely reduced. This clearly poses a problem to the modal model approach. It was suggested by
Shallice and Warrington (1970) that there must be another possible way for information to enter LTM
than via STM. Baddeley and Hitch (1974) drew attention to another problem. Under certain conditions
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it seems to be possible to do two different tasks simultaneously, even though STM, as suggested by
Atkinson and Shiffrin, should be regarded as a single, undivided unit. An example for the performance
of two tasks simultaneously would be the following: a person is asked to memorize 4 numbers and then
read a text (unrelated to the first task). Most people are able to recall the 4 numbers correctly after the
reading task, so apparently both memorizing numbers and reading a text carefully can be done at the
same time. According to Baddeley and Hitch the result of this experiment indicates that the number-
task and the reading-task are handled by two different components of short term memory. So they
coined the term "working memory" instead of "short term memory".
Working Memory
Working memory is defined by Baddeley (2000) as follows: "Working memory is a limited
capacity system for temporary storage and manipulation of information for complex tasks such as
comprehension, learning and reasoning" (p. 162 in Goldstein). What is interesting here is that (a) the
system is limited in its capacity (the same limitations hold as for short term memory) and (b) that the
task of working memory is not only storage, but also manipulation of incoming information. Working
memory consists of three parts: the phonological loop, the visuospatial sketch pad and the central
executive. We will consider each subpart in turn. Let us begin with the phonological loop.
The phonological loop is responsible for auditory and verbal information, such as phone numbers,
person's names or general understanding of what other people are talking about. We could roughly say
that it is a system specialized for language. This system can again be subdivided into an active and a
passive part. The storage of information belongs to the passive part and fades after 2 second if the
information is not rehearsed explicitly. Rehearsal, on the other hand, is regarded as the active part of
the phonological loop. The repetition of information deepens the memory. There are three well-known
phenomena that support the idea that the phonological loop is specialized for language: the
phonological similarity effect, the word-length effect and articulatory suppression. When words that
sound similar are confused, we speak of the phonological similarity effect. The word-length effect
refers to the fact that it is more difficult to memorize a list of long words and better results can be
achieved if a list of short words should be memorized. Let us consider the phenomenon of articulatory
suppression in a little more detail. Consider the following experiment: participants are asked to
memorize words while saying "the, the, the ..." out loud. What we find is that, with respect to the word-
length effect, the difference in performance between lists of long and short words is levelled out. Both
lists can be memorized equally well. The explanation given by Baddeley et al. (1984), who conducted
this experiment, is that the constant repetition of the word "the" prevents the rehearsal of the words in
the lists, independent of whether the list contains long or short words. The findings become even more
drastic if we compare the memory-performance in the following experiment (also conducted by
Baddeley and his co-workers in 1984): participants were again asked to say out loud "the, the, the ...".
But instead of memorizing words from a list of short or long words, their task was to remember words
that were either spoken to them or shown to them written on paper. The results indicated that the
participant's performance was significantly better if the words were presented to them and not read out
aloud. Baddeley concluded from this fact that the performance in a memory task is improved if the two
stimuli can be dealt with in distinct components of the working memory. In other words, because the
reading of words is handled in the visuospatial sketch pad, whereas the saying of "the" belongs to the
phonological loop, the two tasks do not "block" each other. The rather bad performance of hearing
words while speaking could be explained by the fact that both hearing and speaking are dealt with in
the phonological loop and thus the two tasks conflict with each other, decreasing the performance of
memorization.
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In the visuospatial sketch pad visual and spatial information is stored. As we have seen above,
performance decreases if two tasks that are dealt with in the same component are to be done
simultaneously. Let us consider a further example that illustrates this effect. Brandimonte and co-
workers (1992) conducted an experiment where participants were asked to say out loud "la, la, la ...".
At the same time they were given the task of subtracting a partial image from a given whole image. The
subtraction had to be done mentally because the two images were presented only for a short time. The
interesting result was that not only did the performance not decrease while saying "la, la, la ..." when
compared to doing the subtraction-task alone, but the performance even increased. According to
Brandimonte this was due to the fact that the subtraction task was easier if handled in the visuospatial
sketch pad as opposed to the phonological loop (both the given and the resulting pictures were such
that they could also be named, i.e. verbalized, a task that belongs to the phonological loop). In
principle, the participants could freely choose whether they did the subtraction-task verbally or
visually. But because the phonological loop was already occupied by saying "la, la, la ..." and would
therefore have been overloaded if the subtraction-task had been done verbally as well, the participants
were forced to do the task visually. As mentioned above, because of the fact that the subtraction of a
partial image from a whole given image is easier if done visually, the performance increased if
participants were forced to visually perform that task, i.e. if they were forced to use the component that
is suited best for the given task. We have seen that the phonological loop and the visuospatial sketch
pad deal with rather different kinds of information which nonetheless have to somehow interact in
order to do certain tasks. The component that connects those two systems is the central executive.
The central executive co-ordinates the activity of both the phonological loop and the visuospatial
sketch pad. Imagine the following situation: you are driving a car and your friend in the passenger seat
has the map and gives you directions. The directions are given verbally, i.e. they are handled by the
phonological loop, while the perception of the traffic, street lights, etc. is obviously visual, i.e. dealt
with in the visuospatial sketch pad. If you now try to follow the directions given to you by your friend
it is necessary to somehow combine both kinds of information, the verbal and the visual information.
This important connection of the two components is done by the central executive. (It also links the
working memory to long term memory, we will discuss long term memory below.) Currently, research
is being done in order to find out how the central executive solves the complex task of co-ordinating
and controlling the other components. Unfortunately, we do not know much about the operation of the
central executive yet. Let us hope that the research will be as fruitful as it has been so far with respect
to other parts of memory.
Long Term Memory
As the name already suggest, long term memory is the system where memories are stored for a
long time. "Long" in this sense means something between a few minutes and several years or even
decades. Similar to working memory, long term memory can again be subdivided into different types.
Two major distinctions are being made between declarative (conscious) and implicit (unconscious)
memory. Those two subtypes are again split into two components each: episodic and semantic memory
with respect to declarative memory and priming effects and procedural memory with respect to implicit
memory. In contrast to short term or working memory, the capacity of long term memory is
theoretically infinite. The magic number seven obviously does not apply here, because, as mentioned
above, information can be stored for a very long time and is not restricted to a few items. The opinions
as to whether information remains in long term memory for ever, or whether information can get
deleted differ. The main argument for the latter opinion is that apparently not all information that ever
got stored in LTM can be recalled. However, theories that regard long term memories as not being
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subject to deletion emphasize that there might be a useful distinction between the existence of
information and the ability to retrieve or recall that information at a given moment. An example for the
inability to retrieve a particular memory would be a situation in which someone tries to remember a
name, but cannot come up with it. The saying of something like "I have it on the tip of my tongue..."
indicates that the speaker is sure that the information is still existent in his memory, but that the
retrieval is somehow blocked. It such situations the circumstances (in a rather broad sense) might
enhance the retrieval of information. An example would be that someone helps the aforementioned
speaker by giving the first letter of the name or something similar. Or another enhancement might be
that in order to better recall memories about the childhood, it could be helpful to visit the places or
people that are connected to childhood, like the kindergarten or an elementary school teacher.
Declarative Memory
Let us now consider the two types of declarative memory. As noted above, those two types are
episodic and semantic memory. Episodic memory refers to memories for particular events that have
happened to someone. Typically, those memories are connected to specific times and places. Semantic
memory, on the other hand, refers to knowledge about the world that is not connected to personal
events. Vocabulary, concepts, numbers or facts would be stored in semantic memory. The two types
are usually closely related to one another, i.e. memory of facts might be enhanced by interaction with
memory about personal events and vice versa. For example, the answer to the factual question of
whether people put vinegar on their chips might be answered positively by remembering the last time
you saw someone eating fish and chips. The other way around, good semantic memory about certain
things such as football can contribute to more detailed episodic memory of a particular personal event,
like watching a football match. A person that barely knows the rules of that game will most probably
have a less specific memory for the personal event of watching the game than a football-expert will.
Implicit Memory
We now turn to the different types of implicit memory. As the name suggests, both types are
usually active when unconscious memories are concerned. This becomes most evident for procedural
memory, though it must be said that the distinction between both types is not as clearly cut as in the
case of declarative memory and that often both categories are collapsed into the single category of
procedural memory. But if we want to draw the distinction between priming effects and procedural
memory, the latter category is responsible for highly skilled activities that can be performed without
much conscious effort. Examples would be the tying of shoelaces or the driving of a car, if those
activities have been practiced sufficiently. As regards the priming effect, consider the following
experiment conducted by T.J. Perfect and C. Askew (1994). Participants were asked to read a magazine
without paying attention to the advertisements. After that, different advertisements were presented to
them, some had occurred in the magazine, others had not. The participants were told to rate the
presented advertisement with respect to different criteria such as how appealing, how memorable or
eye-catching they were. The result was that in general those advertisements that had been in the
magazine received higher rankings than those that had not been in the magazine. Additionally, when
asked which advertisements the participants had actually seen in the magazine, the recognition was
very poor (only 2.8 of the 25 advertisements were recognized). This experiment shows that the
participants performed implicit learning (as can be seen from the high rankings of advertisements they
had seen before) without being conscious of it (as can be seen from the poor recognition rate). This is
an example of the priming effect.
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Errors in Memory
Finally we arrive at the errors or disorders. A definition of Memory: "Memory is the ability of an
organism to store, retain, and subsequently recall information." So we are on our way to discover what
blocked processes or defective mechanisms of the brain are leading to what kind of disfunction. We
like to divide the errors in biochemical and hardware. (like a brain injury or operation).
Biochemical
A biochemical error is for example alzheimer where patients show a depletion of acetylcholine and
glutamate. "Alzheimer disease is a neurodegenerative disease characterized by progressive cognitive
deterioration together with declining activities of daily living and neuropsychiatric symptoms or
behavioral changes." Alzheimer - Wikipedia
But there are many more Neurodegenerative Diseases. Commonly known are Parkinson, Multiple
sclerosis and Creutzfeld-Jakob. A Neurodegenerative Disease is a "disease caused by the irreversible
deterioration of essential cell and tissue components of the nervous system." . So the basis gets lost and
the brain loses its cognitive functions.
Hardware Errors
The most studied patient with a so called
hardware error is Henry M. H.M.'s History A man
who had as child a bicycle accident and suffered from
epilepsy. In an experimental surgery Dr. William
Scoville removed H.M.'s hippocampus and other parts
of the brain. Good for Henry was that the frequency
of the epilepsy was reduced, bad was that he was not
able to store any new memories. By the way, his
Short Term Memory was normal. Corkin showed in Diagram of basic features of a neuron.
1968 that he could learn new simple tasks. So he concluded that his procedural memory was working.
H.M. is suffering from Anterograde amnesia. Amnesia - Wikipedia
Sources
• E. Bruce Goldstein: Cognitive Psychology: Connecting Mind, Research, and Everyday