Overview of Memory Processes
The Stage Model
Organization and Retrieval in the Long Term Memory
Biological Bases for Memory
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Overview of Memory Processes (top)
Memory is more than a single process.
Memory allows us to acquire, retain and recall information.
The corresponding processes are encoding, storage and retrieval.
encoding = the process of converting information into a form that can be entered and stored in memory
storage = the process whereby an encoded memory is held for future use
retrieval = the process whereby a stored memory is brought into consciousness
Memory is currently thought to have three stages: very short, short and long.
These vary in type of info, function, duration and capacity (see table).
Type of Info
Info from Sensory or Long-Term Memory
Encoded Info from Working Memory
Register Immediate Sensations
Process Input from Sensory Memory & Retrieve Long-Term Memories
Store Lasting Memories
0.25 to 3 seconds
About 30 seconds
Sensory memory briefly holds the tremendous amount of information coming in from the senses. Unless you focus your attention on some part of that information, the memory disappears in about one second.
Short-term memory or working memory holds your current thoughts.
Short-term memory can contain input from two sources:
Short-term or working memory is the problem-solving area of the mind. This is where you remember, imagine or figure things out. Most of the contents of working memory are lost after about 30 seconds, but some is converted to long-term memories.
Long-term memory holds what we usually think of as our memories. Encoded info from working memory is stored here. Previously stored material can be retrieved from long-term memory into working memory.
The Stage Model (top)
Sperling's (b 1934) experiment (1960):
A chart of three rows of four letters each was shown to subjects for 50 milliseconds. Subjects could recall about 4 or 5 of the letters.
Subjects were shown the chart and a tone was sounded within one second of hiding the chart. The tone could be high, medium or low in pitch, signaling the subjects to recall the top, middle or bottom rows of the chart.
If the tone was sounded within about a third of a second, subjects could recall all the letters in the requested row (regardless of which row it was).
If the delay before the tone was more than a third of a second, recall suffered. After about one second, the subjects could not recall what was in each row.
Iconic and echoic memory
Visual sensory memory is sometimes called iconic memory. Auditory sensory memory is sometimes called echoic memory.
Auditory memory lasts a bit longer, up to a few seconds.
This allows us to put words and sentences together. In some cases, I have found that I can "replay the tape" and figure out what someone has said to me even when I didn't think that I heard them.
Short-term memory is the workspace of the mind where sensory info and/or long-term memories can be combined. Short-term memory holds the data used for conscious cognitive activity.
Picture your kitchen. If you face the back of the house, is the stove to the left or the right of the refrigerator.
Is this circle bigger or smaller than your steering wheel?
The capacity of short term memory is about 7 chunks of information, whether each bit is a single number or a more complex set of things.
The capacity of short-term memory can be increased by chunking:
F A U E C P S D A I W T
E P A F D I C T W A U S
New material seems to bump existing material out.
The contents of short-term memory disappear in about 30 seconds, unless you repeat them to yourself over and over.
Maintenance rehearsal is the conscious repetition of the contents to short-term memory. If you are prevented from doing this (5 3 9 6 9)(6 9 12 4 3 5 1 6 7 2 3…) the contents disappear.
Long-term memory is apparently limitless in capacity and duration.
LTM is limited by encoding and retrieval.
Encoding is the process whereby information is put into long-term memory.
Simple repetition (maintenance rehearsal) may help keep things in STM, but it does not work especially well at getting things into LTM.
More effective is to repeat the information in some new meaningful way. This is called elaborative rehearsal because you elaborate on the material.
This is especially useful if you apply the information to yourself (the self-reference effect) and use visual imagery.
Levels of Processing
Craik and Lockhart proposed the levels-of-processing framework in 1972.
Information processed at a deeper level is more likely to be remembered.
This strategy can be useful. To improve your recall of things you are learning:
Baddely proposed the transfer-appropriate processing model in 1992.
Information is better remembered when it is retrieved in a way related to how it was memorized.
Parallel Distributed Processing
Rumelhart and McClelland proposed this model in 1986.
Memories are not isolated bits of info.
Everything that is encoded is added to a semantic network. In other words, what you memorize is added to what you already know.
Information is retained in long-term memory only if it is processed through sensory and short-term memory.
Explicit vs Implicit Memories: Procedural, Episodic, and Semantic Memories
Implicit memories are memories that guide or affect your behavior without your conscious (or verbal) involvement (also known as nondeclarative memories).
Procedural memories tell us how to perform a particular activity.
Procedural memories usually do not include where and when the procedure was learned.
Also, we usually cannot easily describe the contents of a procedural memory in words. For that reason, procedural memories are considered to be implicit memories.
Explicit memories which are memories that can be consciously recalled and described (also known as declarative memories).
Episodic memories refer to episodes or events in the past (One author calls them "biographical details").
The memory usually includes what happened along with when and where it occurred.
Semantic memories are facts, figures, concepts and definitions.
Facts are usually stored without information about when and where they were learned.
Semantic and episodic memories are considered to be explicit memories
Explicit and implicit memories may involve different brain systems.
Organization and Retrieval in the Long Term Memory (top)
When does Wednesday come after Thursday?
Items recalled from long-term memory are clustered or grouped.
The clustering is based on some logical association between the items.
What is the first word that comes into your mind when you hear the word "red"?
Collins & Loftus (1975) proposed the well-known semantic network model.
In this model, each concept is linked with a set of others, which are in turn linked to still others.
A specific iten can be linked with a category (rose® bush) or vice-versa (flower® daisy).
An object can be linked with a characteristic (knife® sharp), and vice-versa.
A place can be linked with an activity (classroom® sleep), and so forth.
The concepts and their links form a network.
Some linkages are stronger than others.
When a concept is activated, the activation can spread to linked concepts, activating them.
The shorter and stronger the chain of linkages, the more quickly one concept leads to another.
Retrieval is the process of putting the contents of long-term memory into working memory.
Retrieval often depends on a retrieval cue, a hint or prompt that triggers the memory.
When you are unable to recall information due to missing, inadequate or inappropriate cues you are experiencing retrieval cue failure.
Very often the unrecalled information is in fact in LTM.
Have you ever had something on the tip of your tongue? The tip-of-the-tongue phenomenon occurs when you have the feeling that you know a piece of information but you can't quite recall it at the moment. These experiences have been studied by a number of memory researchers. Usually some part of the information can be recalled.
About half the time, people can recall the first letter of the word or name they are looking for and often they know the length of the word (in syllables).
Often people produce similar sounding, looking or meaning words.
The recalled bits may serve as cues to retrieve the missing piece.
The missing word usually comes to mind some time after you stop trying to think of it.
Tip-of-tongue experiences highlight that retrieval is not a simple all-or-none process.
There are different types of recall:
Recall or free recall is the retrieval of information with no cues.
Cued recall is the retrieval of information in response to a cue (complete the sentence).
Recognition is simply identifying a piece of retrieved information (as on a multiple choice test).
Serial recall is the retrieval of information in order.
It doesn't do you much good to remember the directions to a friends house unless you remember them in order: "I know how to get there. You take six lefts and four rights."
Sometimes each list item cues recall of the next: I remember students more easily in alphabetical order.
The serial position effect refers to the relative ease of recalling items at different positions on a list.
primacy effect: items at the beginning of the list are more easily recalled
recency effect: items at the end of the list are more easily recalled
The Encoding Specificity Principle
Recreating the original learning conditions improves retrieval.
I remember students names more easily if they don't move around in the room.
The Context Effect
An encoded memory may include more than the specific piece of info that was being learned, such as environmental stimuli present at the time of learning.
These stimuli can serve as cues to aid in the retrieval of the learned information.
I have an easier time remembering students' names in class than in the grocery store.
There seems to be a hierarchy of contexts: the closer the context to the original, the easier it is to recall (I recently saw a student on Block Island, although he looked familiar, it took me several minutes to realize that he was a student; I couldn't recall his name for about a half hour).
Students do better on exams when tested in the room where they learned.
A memory may include not only external cues (as in the context effect) but also internal cues.
Free recall of things learned while intoxicated is slightly better when done intoxicated (though overall, learning and recall is worse when you are intoxicated).
When you feel good, you have happy memories; when you are blue, you have sad memories.
Where were you when you heard that OJ Simpson had been found not guilty?
A flashbulb memory is proposed to involve the retrieval of a number of details surrounding a rare and striking event.
Neisser & Harsch (1992) carried out an experiment on flashbulb memories:
Immediately after the Challenger disaster, students wrote down what they had been doing when they heard the news. Three years later, they were asked to recall the same things.
Most of the students were very confident of their recollections, but about a third were wrong. Seeing the proof of their errors, these students still felt confident that their memories were correct.
False Memories (top)
A schema is an organized set of concepts about a particular thing (person, setting, location, idea, etc).
Schemas are helpful when we form new memories.
Provide pigeon holes into which to place new info.
Highlight unusual (memorable) details
Schemas can cue recall.
In some cases, the schema may fill in missing details from a memory, with the result that the memory is wrong.
In one study (Spiro 1980) students read a happy little story about Bob and Margie, who were engaged. Some subjects were offhandedly told that Bob and Margie broke up.
The "break up" subjects supplied additional details when recalling the story.
When the true source of a memory is forgotten, the recollection can be distorted due to source confusion.
Details are remembered incorrectly--details from different events (or from no event) may be combined.
The recollection may be quite vivid (though wrong). After all, it is based on some things that are actually remembered.
Elizabeth Loftus (b 1944) has studied false memories extensively. She has actually given expert testimony on the subject in many legal cases.
In 1974 she did published the results of an experiment in which subjects were shown a film of an auto accident.
Subjects were told to write a description of what they saw and answer a few questions.
One of the questions in some of the questionnaires was "About how fast were the cars going when they contacted each other?" In other questionnaires the word "contacted" was replaced with "bumped," "collided," "hit" or "smashed."
The results were as given in the chart: The word choice caused remembered speed estimates to vary by nearly 30%.
People with retrograde amnesia are unable to remember part or all of their past, particularly episodic information.
Often, people are unable to recall what occurred just before they received a blow to the head.
This is thought to be due to a failure of memory consolidation.
A new long-term memory trace is apparently easily lost.
People with anterograde amnesia are unable to form new long-term memories; short-term memory and existing long-term memory may be fine.
Explicit memories are more affected than implicit memories (anterograde amnesia usually does not affect the formation of procedural memories).
This is seen in cases of damage to the hippocampus, which seems to be involved in the encoding and transfer of new long-term memory traces.
What is your earliest memory?
Most people cannot remember the first two years or so of life. There are a number of proposed explanations for this:
Encoding specificity: the world of an adult is too different from the world of an infant to provide adequate retrieval cues.
Brain development: the hippocampus may not mature until about age two. If so, infants may be able to form procedural memories but not episodic memories.
The Forgetting Curve
Ebbinghaus (1850-1909) studied memory in himself.
He found that he forgot more than 50% of memorized nonsense syllables in less than an hour.
Most of what he remembered after 8 hours, he remembered after a month.
He plotted his results in the now famous "forgetting curve."
Factors in Forgetting
A common reason for inability to recall is failure to encode in the first place.
Simple repetition is not enough to encode a long term memory (which way does Washington face on a quarter?)
Retroactive interference occurs when a new memory interferes with the recall of an older one.
Proactive interference occurs when an older memory interferes with the recall (or encoding) of a newer one.
There may be cases in which we would like to forget something, such as a trauma.
Suppression refers to intentional, conscious, forgetting of information.
This may not be possible.
Repression refers to unconscious, but motivated, blocking of memories.
This is a hot topic:
The idea that repressed memories affect behavior is widely accepted by clinicians and the general public.
Among researchers, there are those who do not believe that repression occurs as well as those who hold it responsible for a myriad of psychological problems. Still others memory researchers propose that extreme emotion can disrupt memory but believe that the case for repression is far from clear.
Decay theory holds that an unused memory trace disappears with time.
This is not supported by research that shows that strong cues can brink back old, unused memories.
Biological Bases for Memory (top)
The Memory Trace (aka the "engram")
In the 1920's, a zoologist named Lashley (1890-1958) began a search for brain changes connected to memory formation.
Lashley initially believed that the changes were specific and localized.
He found that there was no part of the cerebral cortex that was required for retention of complex long-term memories.
Ie, a maze-trained rat could still run the maze after any piece of its cortex was surgically removed.
Lashley concluded that memory is distributed in the brain.
In contrast, in the late 70's, a psychologist named Thompson (b 1930) studied brain changes associated with classical conditioning in rabbits.
He conditioned rabbits to blink in response to a tone (by pairing it with a puff of air).
He observed changes in a small part of the cerebellum. If this part was removed, the conditioned reflex disappeared (though not the native reflex).
Memory appears to be both localized and distributed.
PET scans confirm that memory tasks require the involvement of a range of brain areas.
Neuronal Correlates of Long-Term Memory
Memory seems to involve changes in both the function and the structure of neurons.
At least memory in snails does, as demonstrated by Kandel and others in the last decade:
Aplysia is a Pacific sea snail with a very simple nervous system (about 20,000 neurons).
If you give the snail a slight shock following a squirt of water, the snail soon begins to withdraw its gill flap in response to the squirt alone.
The conditioned reflex is accompanied by changes in three neurons (the one that detects the squirt, the one that detects the shock and the one that withdraws the gill flap):
The amount of neurotransmitter released by the neurons increases.
The number of branches on the dendrites and the number of synaptic connections increases.
Similar changes have been observed in mammals.
These changes are described as the formation of a memory circuit in the nervous system.
Brain Structures Active in Memory
active in putting remembered events in order (though not in remembering the events themselves)
Medial Temporal Lobe
active in encoding and storing explicit memories
active in memories involving movement
active in emotional memories
active in combining different sense modalities in memory
active in encoding and storing explicit memories
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Anthony G Benoit