Memory is imperfect. This is because we often do not see things accurately in the first place. But even if we take in a reasonably accurate picture of some experience, it does not necessarily stay perfectly intact in memory. Another force is at work. The memory traces can actually undergo distortion. With the passage of time, with proper motivation, with the introduction of special kinds of interfering facts, the memory traces seem sometimes to change or become transformed. These distortions can be quite frightening, for they can cause us to have memories of things that never happened. Even in the most intelligent among us is memory thus malleable.
Elizabeth Loftus, Memory: Surprising New Insights into How We Remember and Why We Forget
Human memory has served as plot fodder for science fiction for years. In “We Can Remember It for You Wholesale,” a short story by Philip K. Dick, REKAL Incorporated can implant “extra-factual memories” – memories of things that never happened that are “more real than the real thing.” In The Golden Age by John Wright, the novel’s posthuman protagonist has deleted the last 300 years of his memories — including, of course, the memory of doing so. As he tries to reconstruct why, he learns that everyone else deleted their memories of him as well. And in the movie Inception, a team of corporate spies infiltrate people’s dreams to discover information and plant false memories.
So what do we really know about human memory? How accurate is it? Can it be manipulated, and if so, how? Using Harvard University psychology professor Daniel Schacter’s book, The Seven Sins of Memory as a guide, let’s look at what we know, think we know, and aren’t sure we know about the fallibility of human memory.
Transience: a decreasing memory over time
In 1885, German psychologist Hermann Ebbinghaus published his groundbreaking article “Über das Gedchtnis” (“Memory: A Contribution to Experimental Psychology”) in which he described experiments he conducted on himself to describe the process of forgetting. In order to test for new information, Ebbinghaus tested his memory for periods of time ranging from 20 minutes to 31 days, memorizing nonsense syllables, such as “WID” and “ZOF”. By repeatedly testing himself after various time periods and recording the results, he was the first to describe the shape of what is known as the Ebbinghaus forgetting curve, which revealed a relationship between forgetting and time. Initially, information is often lost very quickly after it is learned. Factors such as how the information was learned and how frequently it was rehearsed play a role in how quickly these memories are lost. The stronger the memory, the longer one retains it. A typical graph of the forgetting curve shows that humans tend to halve their memory of newly learned knowledge in a matter of days or weeks unless they consciously review the learned material.
Transience can be seen in both short- and long-term memory. For psychologists, short-term memory, means just the things that are in your mind right now, while long-term memory is anything you store to be retrieved at a later time. Studies have shown that both types of memory can be extremely fragile over their respective timescales. In Schacter’s, The Seven Sins of Memory, he describes how several days after the acquittal of O.J. Simpson, a group of California undergraduates provided researchers with detailed accounts of how they learned about the jury’s verdict. When the researchers tested students’ memories 15 months later about the verdict, only half recalled accurately how they found out about the decision. Asked again nearly three years after the verdict, less than 30% of students’ recollections were accurate; nearly half were dotted with major errors.
Absent-mindedness: forgetting to do things
This is memory loss resulting from failure to pay attention when carrying out an act—putting your keys or glasses down without registering where you’re putting them. Schacter uses the example of cellist Yo Yo Ma. In October 1999, Ma left his $2.5 million cello, made in 1733 by Antonio Stradivari, in a New York cab. Apparently, he was preoccupied with other things and forgot to remind himself to ask the cab driver to retrieve his cello from the trunk.
There are two central factors in how and why we are absent-minded. One is how much attention we’re paying at the crucial moment, the other is how deeply we encode a memory.
A classic study demonstrates how central attention is to absent-mindedness. In 1999, an experiment on change-blindness was conducted by D. J. Simons and C. F. Chabris. Participants watched a video of people passing a basketball between each other, and were asked to count the number of passes. After about 30 seconds of people passing the basketball, a person dressed in a gorilla suit walks right through the center of the scene, stops, turns, looks at the camera, then turns again and walks out of shot. On average around half the people who took part didn’t notice the gorilla.
Another classic experiment demonstrates how the depth at which we process information affects our absent-mindedness. In 1975, Fergus Craik and Endel Tulving set about testing the strength of memory traces created using three different levels of processing:
1. Shallow processing: participants were shown a word and asked to think about the font it was written in.
2. Intermediate processing: participants were shown a word and asked to think about what it rhymes with.
3. Deep processing: participants were shown a word and asked to think about how it would fit into a sentence, or which category of “thing” it was.
Participants who encoded the information most deeply remembered the most words when given a surprise test later. But it also took them longer to encode the information in the first place. But most importantly, participants had to do the right type of encoding. For example considering a word’s meaning for a long time did help its recall, but putting equivalent effort into thinking about its structure didn’t.
Another type of absent-mindedness involves prospective memory – trying to remember to do something in the future. These tasks involve setting a mental alarm clock triggered either by some event occurring, like leaving work, or by a particular time. Psychologists have found the ways in which we are absent-minded in prospective memory can depend on whether we’re trying to remember a future event or a future time. Normally we depend on external cues to jog our memories, such as looking at a clock, or at a note we’ve left ourselves. We usually forget event-based prospective memories when we don’t see the cue. We don’t notice the clock, for example, because we’re in a hurray to get somewhere. Time-based prospective memories depend more on how good we are at generating cues for ourselves. For example, someone might remember to brush their at the same time by always doing as soon as they wake up and right before going to bed.
Absent-mindedness can have can have disastrous consequences. A pilot forgets a crucial item on their takeoff checklist and misses a problem that causes the plane to crash, or a surgeon forgets to suture an artery when finishing operating on a patient that causes them to die from internal bleeding. But sometimes it can be a blessing. Take the case of the Russian journalist Solomon Shereshevskii. Shereshevskii’s memory was so perfect he could remember everything he heard or read. But he found it difficult to ignore insignificant events. A sneeze or cough would be imprinted on his memory forever. And his memories were so highly detailed he found it difficult to think in the abstract or know which facts were important and which weren’t. Shereshevskii eventually became a social recluse; ending up a prisoner to his immense memory.
Blocking: the tip-of-the-tongue experience
This is characterized by being able to retrieve quite a lot of information about the target word without being able to retrieve the word itself. You may know the meaning of the word, how many syllables the word has, or its initial sound or letter, but you can’t retrieve it. The experience is coupled with a strong feeling you know the word and that it’s hovering on the edges of your thought. Studies on blocking have shown that around half of the time we will become ‘unblocked’ after about a minute. The rest of the time it may take days to recover the memory.
A study published in the journal Neuron, shows that we’re also able to voluntarily forget things. Researchers were able to discover two methods of forgetting by conducting fMRI brain scans on volunteers as they remembered, and then purposely forgot, associations between word pairs. The first way is to essentially stop the brain’s remembering system from working, trying to block them out entirely. The second way is to have a substitute memory for the brain to remember instead of the one we want to block out, thinking about other things that would replace memories of the associations.
Another type of blocking is said to be caused by experiences so horrific that the human brain seals them away, only to be recalled years later either spontaneously or through therapy. This type of blocking, known by the diagnostic term dissociative amnesia and more colloquially as recovered memories. In Sigmund Freud’s theory of “repression” the mind automatically banishes traumatic events from memory to prevent overwhelming anxiety. Freud further theorized that repressed memories cause “neurosis,” which could be cured if the memories were made conscious.
The theory of unconsciously repressing the memory of traumatic experiences is controversial. Most psychologists accept as fact that it’s common to consciously repress unpleasant experiences, and to spontaneously remember such events long afterward. Most of the controversy centers around recovered memories during repressed memory therapy (RMT). Critics of RMT maintain that many therapists are not helping patients recover repressed memories, but are suggesting and planting false memories of alien abduction, sexual abuse, and satanic rituals.
During the 1980s, claims of childhood sexual abuse based on recovered memories led to numerous highly publicized court cases. A number of the supposed victims retracted their allegations in the early 1990s, saying they had been swayed by therapeutic techniques. The argument continued throughout the 1990s, driven by high profile cases such as that of actress Roseanne Barr, and by people who claimed that their abusers had been set free because of testimony against repressed memories by psychologists such as Elizabeth Loftus, a research psychologist who has devoted her life to the study of memory.
So how real are repressed memories? Some argue that it’s plausible that memories of childhood sexual abuse could be buried for years and then recalled, and that motivated forgetting, dissociative amnesia, or some other mechanism could account for repressed memories. Others argue that the idea of recovered repressed memories is implausible, contradicting a) that vivid experiences (as sexual abuse would presumably be) create lasting memories, b) memories change and are reconstructed over time, even those that are easily accessible and frequently recalled, and c) thoughts that we experience as remembered may come from sources other than memories of actual experiences of our own.
Next time I’ll look at the remaining four sins of memory.
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