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Memory is the retention of, and ability to recall, information, personal experiences, and procedures (skills and habits).
There is no universally agreed upon model of the mind/brain, and no universally agreed upon model of how memory works. Nevertheless, a good model for how memory works must be consistent with the subjective nature of consciousness and with what is known from scientific studies (Schacter 1996). Subjectivity in remembering involves at least three important factors:
- Memories are constructions made in accordance with present needs, desires, influences, etc.
- Memories are often accompanied by feelings and emotions.
- Memory usually involves awareness of the memory (Schacter 1996).
Two models of thinking which are popular with materialists are the behaviorist model (thinking is a set of behaviors) and that of cognitive psychology (the brain is like a computer). Neither can account for the subjective and present-need basis of memory (Schacter 1996). The Freudian model posits an area of the unconscious where memories of traumatic experiences are stored. These unconscious memories are claimed to be significant causal factors in shaping conscious thought and behavior. This model is not consistent with what is known about the memory of traumatic experiences. There is a great deal of supportive evidence for the claim that the more traumatic an experience, the more likely one is to remember it. Novel visual images, which would frequently accompany traumas, stimulate the hippocampus and left inferior prefrontal cortex and generally become part of long-term memory.
Current studies in neuroscience strongly support the notion that a memory is a set of encoded neural connections. Encoding can take place in several parts of the brain. Thus, neural connections are likely to go across various parts of the brain. The stronger the connections, the stronger the memory. Recollection of an event can occur by a stimulus to any of the parts of the brain where a neural connection for the memory occurs. If part of the brain is damaged, access to any neural data that was there is lost. On the other hand, if the brain is healthy and a person is fully conscious when experiencing some trauma, the likelihood that they will forget the event is nearly zero, unless either they are very young or they experience a brain injury.
Furthermore, the Freudian model often assumes that childhood sexual abuse is usually unconsciously repressed and that psychological problems in adulthood are caused by the unconscious memory of childhood abuse. There is, however, no body of scientific evidence to support either that such abuse is unconsciously repressed or that these experiences are significant causal factors of adult psychological problems.
Finally, the model of memory that sees the brain recording everything one experiences is a model that contradicts what is known about how memories are constructed. Even so, in a survey of psychologists by Loftus and Loftus, 84% said they believe every experience is permanently stored in the mind (Schacter 1996, 76).
a popular model of memory
One of the most popular models of memory sees memory as a present act of consciousness, reconstructive of the past, stimulated by an analogue of an engram called the "retrieval cue." The engram is the neural network representing fragments of past experiences which have been encoded. The evidence is strong that there are distinct types and elements of memory which involve different parts of the brain, e.g., the hippocampus and ongoing incidents of day-to-day living (short-term or working memory); the amygdala and emotional memories (Schacter 1996, 213). Memories might better be thought of as a collage or a jigsaw puzzle than as "tape recordings," "pictures" or "video clips" stored as wholes. On this model, perceptual or conscious experience does not record all sense data experienced. Most sense data is not stored at all. What is stored are bits and fragments of experience which are encoded in engrams. Exactly how they are encoded is not completely understood.
This popular model of memory rejects the idea that individual memories are stored in distinct locations in the brain. That idea seems to have become solidified by Wilder Graves Penfield's experiments done in the 1950s. He placed electrodes on the surface of the exposed temporal lobes of patients and was able to elicit "memories" in 40 of 520 patients. Many psychologists (and lay people) refer to these experiments as proof that memories are just waiting for the right stimulus to be evoked. Schacter points out that the Penfield experiments are not very good evidence for this belief. Penfield could only elicit "memories" in about one out of every thirteen patients. Furthermore, he did not provide support for the claim that what was elicited was actually a memory and not a hallucination, fantasy, or confabulation.
On the model described in the previous two paragraphs, forgetting is due to either:
- weak encoding (why we forget most things, including our nightly dreams);
- lack of a retrieval cue (we seem to need something to stimulate memory);
- time and the replacement in the neural network by later experiences (how many experiences do you remember from many years ago?);
- repetitive experiences (you'll remember the one special meal you had at a special restaurant, but you won't remember what you had for lunch a year ago Tuesday), or
- a drive to keep us sane. (Imagine the brain overload that would occur if we were to never forget anything, the stated goal of L. Ron Hubbard's dianetics. His followers should read Jorge Luis Borges's "Funes, the Memorious," a story about such a being.)
An additional reason for forgetting may have something to do with dreaming:
In the quiet of night your brain may turn the day's events into dreams. Through dreams your brain may examine those events and make sense of them. It may erase some and add others to your memory bank.*
The chances of remembering something improve by "consolidation," which creates strong encoding. Thinking and talking about an experience enhance the chances of remembering it. One of the better known techniques of remembering involves the process of association.
Many people have vivid and substantially accurate memories of events which are erroneous in one key aspect: the source of the memory. For example:
In the 1980 presidential campaign, Ronald Reagan repeatedly told a heartbreaking story of a World War II bomber pilot who ordered his crew to bail out after his plane had been seriously damaged by an enemy hit. His young belly gunner was wounded so seriously that he was unable to evacuate the bomber. Reagan could barely hold back his tears as he uttered the pilot's heroic response: "Never mind. We'll ride it down together." ...this story was an almost exact duplicate of a scene in the 1944 film "A Wing and a Prayer." Reagan had apparently retained the facts but forgotten their source (Schacter 1996, 287).
An even more dramatic case of source amnesia (also called memory misattribution) is that of the woman who accused memory expert Dr. Donald Thompson of having raped her. Thompson was doing a live interview for a television program just before the rape occurred. The woman had seen the program and "apparently confused her memory of him from the television screen with her memory of the rapist" (Schacter 1996, 114). Studies by Marcia Johnson et al. have shown that the ability to distinguish memory from imagination depends on the recall of source information.
Tom Kessinger, a mechanic at Elliott's Body Shop in Junction City, Kansas, gave a detailed description of two men he said had rented a Ryder truck like the one used in the Oklahoma City bombing of the Alfred P. Murrah Federal Building. One looked just like Timothy McVeigh. The other wore a baseball cap and a T-shirt, and had a tattoo above the elbow on his left arm. That was Todd Bunting, who had rented a truck the day before McVeigh. Kessinger mixed the two memories but was absolutely certain the two came in together.
Jean Piaget, the great child psychologist, claimed that his earliest memory was of nearly being kidnapped at the age of two. He remembered details such as sitting in his baby carriage, watching the nurse defend herself against the kidnapper, scratches on the nurse's face, and a police officer with a short cloak and a white baton chasing the kidnapper away. The story was reinforced by the nurse, the family, and others who had heard the story. Piaget was convinced that he remembered the event. However, it never happened. Thirteen years after the alleged kidnapping attempt, Piaget's former nurse wrote to his parents to confess that she had made up the entire story. Piaget later wrote that "I therefore must have heard, as a child, the account of this story...and projected it into the past in the form of a visual memory, which was a memory of a memory, but false" (Tavris 1993).
Though all forgetting is a type of amnesia, we usually reserve that term for forgetting that is caused by the effects of drugs/alcohol, brain injuries, or physical or psychological traumas. One of the more interesting types of amnesia is what psychiatrists call the fugue state. An otherwise healthy person travels a good distance from his home, and when found has no memory of how he got there or who he is. The fugue state is usually attributed to recent emotional trauma. It is rare and is typically neither permanent nor recurring.
Limited amnesia, however, is quite common. Limited amnesia occurs in people who suffer a severe physical or psychological trauma, such as a concussion or being rendered unconscious. Football players who suffer concussions, and accident victims who are rendered unconscious, typically do not remember what happened immediately before the event. The scientific evidence indicates, however, that some sort of implicit memory may exist, which can be troubling to one whose amnesia is due to having been rendered unconscious by an assailant. Schacter notes the case of a rape victim who could not remember the rape, which took place on a brick pathway. The words 'brick' and 'path' kept popping into her mind, but she did not connect them to the rape. She became very upset when taken back to the scene of the rape, though she didn't remember what had happened there (Schacter 1996, 232).
Implicit memory is memory without awareness. It differs substantially from repressed memory. Implicit memories are not necessarily repressed, nor are they necessarily the result of trauma. They are weakly encoded memories which can affect conscious thought and behavior. Retrieval cues do not bring about a complete memory of some events because most of the event was not encoded.
Daniel Schacter and Endel Tulving introduced the terms 'implicit memory' and 'explicit memory' in their attempt to find a common language for those who believe there are several distinct memory systems and those who maintain there is only one such system. Schacter writes: "The nonconscious world of implicit memory revealed by cognitive neuroscience differs markedly from the Freudian unconscious. In Freud's vision, unconscious memories are dynamic entities embroiled in a fight against the forces of repression; they result from special experiences that relate to our deepest conflicts and desires. . . .[I]mplicit memories . . . arise as a natural consequence of such everyday activities as perceiving, understanding, and acting" (Schacter, 1996, 190-191).
Most lost memories are lost because they were never elaborately encoded. Perception is mostly a filtering and defragmenting process. Our interests and needs affect perception, but most of what is available to us as potential sense data will never be processed. And most of what is processed will be forgotten. Amnesia is not rare, but is the standard condition of the human species. We do not forget simply to avoid being reminded of unpleasant things. We forget either because we did not perceive closely in the first place or we did not encode the experience either in the parietal lobes of the cortical surface (for short-term or working memory) or in the prefrontal lobe (for long-term memory).
Long-term memory requires elaborative encoding in the inner part of the temporal lobes. If the left inferior prefrontal lobe is damaged or undeveloped, there will be grave difficulty with elaborative encoding. This area of the brain is undeveloped in very young children (under the age of three). Hence, it is very unlikely that any story of having a memory of life in the cradle or in the womb is accurate. The brains of infants and very young children are capable of storing fragmented memories, however. Such memories cannot be explicit or deeply encoded, but they can nevertheless have influence. In fact, there are numerous situations--such as cryptomnesia-- where memory can be manifested without awareness of remembering.
semantic, procedural, and episodic memory
Memory researchers distinguish several types of memory systems. Semantic memory contains conceptual and factual knowledge. Procedural memory allows us to learn new skills and acquire habits. Episodic memory allows us to recall personal incidents that uniquely define our lives (Schacter, 1996, 17). Another important distinction is that between field and observer memory. Field memories are those where one sees oneself in the scene. Observer memories are those seen through one's own eyes. The fact that many memories are field memories is evidence, as Freud noted, of the reconstructive nature of memories (Schacter, 1996, 21).
accuracy of memory
How accurate and reliable is memory? Studies on memory have shown that we often construct our memories after the fact, that we are susceptible to suggestions from others that help us fill in the gaps in our memories. That is why, for example, a police officer investigating a crime should not show a picture of a single individual to a victim and ask if the victim recognizes the assailant. If the victim is then presented with a line-up and picks out the individual whose picture the victim had been shown, there is no way of knowing whether the victim is remembering the assailant or the picture.
Another interesting fact about memory is that studies have shown that there is no significant correlation between the subjective feeling of certainty a person has about a memory and the memory being accurate. Also, contrary to what many people believe, hypnosis does not aid memory's accuracy. Because subjects are extremely suggestible while hypnotized, most states do not allow as evidence in a court of law testimony made while under hypnosis (Loftus, 1979).
Furthermore, it is possible to create false memories in people's minds by suggestion, even false memories of previous lives. Memory is so malleable that we should be very cautious in claiming certainty about any given memory without corroborative evidence. Researchers have found that false memories can be created by manipulating photos of historical events. The doctored images can be used inadvertently or intentionally to alter the memory of the event and affect beliefs and future behaviors.*
How does memory work?
We do not know exactly how memory works, though there are many explanatory models for memory. Some of these models identify memory with brain functions. On this model, for example, memory diminishes with age because neurons die off as we get older. There are only three ways to overcome this fact of nature: 1. figure out a way to stop neurons from dying; 2. stimulate the growth of new neurons; or 3. figure out a way to get the remaining neurons to function more efficiently and pick up the slack. So far, it looks like options 2 and 3 are the most promising. Since 1997 there has been evidence that brain cells do divide.* "The discovery of life-long neurogenesis in humans has redefined our understanding of the brain and spinal cord."* Some positive results have been reported regarding the stimulation of the growth of new brain cells by fetal implants. Fred Gage of The Salk Institute has reported that recent research in neurogenesis is encouraging. They have observed the growth of neurons in the dentate gyrus, a portion of the hippocampus (which controls learning and short term memory), in mice that were placed in a stimulating environment. Gage has also grafted immature cells from the spinal cord to the hippocampus and found that they produced new neuronal cells. There is also growing support for the notion that exercising the body and the brain tend to preserve neurons. "Use it or lose it" turns out to be literally true for brain cells.
Neurological research has also produced some success getting neurons to work better with ampakines, chemical compounds sometimes called "memory drugs." The first tests with humans showed excellent results, but the samples were too small to justify drawing any conclusion except that more studies are needed.
For those who think that memory is a function of some non-physical reality, such results should cause some reflection, though I doubt that a non-physical model of the mind will lead to any significant research which will benefit humankind. For those who posit that memory is a brain function, there is not only a direction for research to follow, but hope of success for discovering something truly useful.
books and articles
Gardner, Martin. (2006). "The Memory Wars." Skeptical Inquirer. Part 1 is in vol. 30 no. 1, parts 2 and 3 are in vol. 30 no. 2.
Loftus, Elizabeth F. Memory, Surprising New Insights Into How We Remember and Why We Forget (Reading, Mass.: Addison-Wesley Pub. Co., 1980).
Tavris, Carol. "Hysteria and the incest-survivor machine," Sacramento Bee, Forum section, January 17, 1993.
Ministry of Truth: A mass experiment in altering political
memories by William Saletan, Slate
This is an article on the work of Elizabeth Loftus.
Review of Daniel Schacter's Searching for Memory
Molecules and synapses cement memories, say scientists "...scientists at the University of California Santa Barbara say their laboratory work on rats shows the production of proteins needed to cement memories can only happen when the RNA - the collection of molecules that take genetic messages from the nucleus to the rest of the cell - is switched on.
Until it is required, the RNA is paralysed by a "silencing" molecule - which itself contains proteins.
When an external signal comes in - for example when one sees something interesting or has an unusual experience - the silencing molecule fragments and the RNA is released."
The neurological basis of intuition (Intuition may be an expression of implicit memory.)
Unmaking Memories: Interview with James McGaugh Scientific American