Reprinted from: MemoryLifter, Learning Theory - How
are Things Remembered
http://www.memorylifter.com/
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Memory Retrieval
Hermann Ebbinghaus was an early pioneer in trying to understand how the
human brain remembers things. Ebbinghaus brought learning and memory into
the laboratory (1890s through the 1920s) where he very carefully devised
various experiments to measure, codify and quantify various aspects about
how we remember and how we do not remember. This pioneering work was done
with the memorization of nonsense syllables to remove various cultural
biases in remembering and evolved into very specific formula describing
retention of the data learned.
At the risk of oversimplifying the results Ebbinghaus found that without
repetition or other encoding methods that the memory decayed at rather an
exponential rate. We tend to forget about 75% of what we learn after only
48 hours without special encoding.
Forgetting - When Memory does not Work
Most of what goes into our brains is not retained for long. The brain is
constantly flooded with information from our senses, so it develops the
ability to dispense with most of this information that it does not need.
Ebbinghaus work clearly showed a value in trying to encode the information
into long term memory via repetition and rehearsal. His experiments
clearly showed that recalling ability was vastly improved by repeatedly
reviewing the material to be remembered. It took a smaller and smaller
amount of effort to memorize things so that the recalling ability would
remain at higher levels for longer times.
The speed of forgetting is influenced by the difficulty of the material to
be remembered, its representation such as mnemonics, and many
physiological factors such as stress and attentiveness.
Building on this seminal work by Ebbinghaus another European psychologist
Sebastian Leitner about 65 years later devised a cardbox methodology for
learning with flashcards. His cardbox methodology is based on very simple
rules of operation. The cardbox is divided into multiple sections with
succeeding sections being geometrically larger than preceding sections.
Starting with an unlimited number of cards in a card pool ten cards are
picked for learning and presented one at a time for learning. If the card
is known then it is put into the second box. If the card is not known then
it is put into the first section of the box. As each flashcard is learned
it is promoted to the back of the next box. If the flashcard is unknown it
is put in back of the deck in the first section.
With this rotation things that are driven into Long Term Memory are
repeated seldom and those things that are difficult to learn are presented
more often for memorization. This simple system removes the biases
associated with counting and makes record keeping automatically by card
positions within the CardBox.
Rate of Decay of Memory
Ebbinghaus developed an ingenious way to measure forgetting. In order to
avoid the influence of familiar material, he created dozens of lists of
nonsense syllables, which consisted of pronounceable but meaningless
three-letter combinations such as XAK or CUV. He would learn a list by
repeating the items in it over and over, until he could recite the list
once without error. He would note how many trials or how long it took him
to learn the list. He then tested his memory of the list after an interval
ranging from 20 minutes to 31 days. He measured how much he had forgotten
by the amount of time or the number of trials it took him to relearn the
list. By conducting this experiment with many lists, Ebbinghaus found that
the rate of forgetting was relatively consistent. Forgetting occurred
relatively rapidly at first and then seemed to level off over time. Other
psychologists have since confirmed that the general shape of the
forgetting curve holds true for many different types of material. Some
researchers have argued that with very well learned material, the curve
eventually flattens out, showing no additional forgetting over time.
Ebbinghauss forgetting curve illustrated the loss of information from
long-term memory. Researchers have also studied rate of forgetting for
Working memory. In one experiment, subjects heard an experimenter speak a
three-letter combination (such as CYG or FTQ). The subjects task was to
repeat back the three letters after a delay of 3, 6, 9, 12, 15, or 18
seconds. To prevent subjects from mentally rehearsing the letters during
the delay, they were instructed to count backward by threes from a random
three-digit number, such as 361, until signaled to recall the letters. As
shown in the accompanying chart entitled Duration of Working Memory,
forgetting occurs very rapidly in this situation. Nevertheless, it follows
the same general pattern as in long-term memory, with sharp forgetting at
first and then a declining rate of forgetting. Psychologists have debated
for many years whether short-term and long-term forgetting have similar or
different explanations.
The oldest idea about forgetting is that it is simply caused by decay.
That is, memory traces are formed in the brain when we learn information,
and they gradually disintegrate over time. Although decay theory was
accepted as a general explanation of forgetting for many years, most
psychologists do not lend it credence today.
Interference Forgetting
According to many psychologists, forgetting occurs because of interference
from other information or activities over time. A now-classic experiment
conducted in 1924 by two American psychologists, John Jenkins and Karl
Dallenbach, provided the first evidence for the role of interference in
forgetting. The experimenters enlisted two students to learn lists of
nonsense syllables either late at night (just before going to bed) or the
first thing in the morning (just after getting up). The researchers then
tested the students memories of the syllables after one, two, four, or
eight hours. If the students learned the material just before bed, they
slept during the time between the study session and the test. If they
learned the material just after waking, they were awake during the
interval before testing. The students forgot significantly more while they
were awake than while they were asleep. Even when wakened from a sound
sleep, they remembered the syllables better than when they returned to the
lab for testing during the day. If decay of memories occurred
automatically with the passage of time, the rate of forgetting should have
been the same during sleep and waking. What seemed to cause forgetting
was not time itself, but interference from activities and events occurring
over time.
Repression of Memory
Another possible cause of forgetting resides in the concept of repression,
which refers to forgetting an unpleasant event or piece of information due
to its threatening quality. The idea of repression was introduced in the
late 19th century by Austrian physician Sigmund Freud, a founder of
psychoanalysis. According to Freudian theory, people banish unpleasant
events into their unconscious mind. However, repressed memories may
continue to unconsciously influence peoples attitudes and behaviors and
may result in unpleasant side effects, such as unusual physical symptoms
and slips of speech. A simple example of repression might be forgetting a
dentist appointment or some other unpleasant daily activity. The concept
of repression is complicated and difficult to study scientifically. Most
evidence exists in the form of case studies that are usually open to
multiple interpretations. For this reason, many memory researchers are
skeptical of repression as an explanation of forgetting, although this
verdict is by no means unanimous.
MemoryLifter does not take any specific recognition of why we forget just
that we do. The MemoryLifter Algorithm is optimized to control the spacing
interval of information presentation so that those items that are known
are repeated less often at ever longer intervals while things that have
not been learned are presented more frequently with shorter intervals
between presentation. If the user simply uses MemoryLifter on a regular
basis the presentation frequency and spacing intervals will be controlled
to provide the maximum memory performance.
Summary of Memory
Memory can be thought of in three stages or sections - Sensory memory
where things are continuously entering from our senses - Working memory
where we are working on trying to encode things or recall things and Long
Term memory where things are stored for use later. Things are encoded from
Working memory into Long Term memory and recalled by decoding access to
them. While this simplistic model may not match detailed psychological
explanations of how the mind works, it is not at odds with most thinking
today about memory. It is adequate for the rest of our discussion.