Forgetting over Time
Anterograde amnesia refers to memory loss due to an inability to transfer information from short-term to long-term memory. Anterograde amnesia can be caused by brain injuries or diseases. Anterograde amnesia caused by chronic alcohol abuse is called Korsakoff syndrome. It occurs because alcohol inhibits the absorption of thiamine, a B vitamin that is vital to brain function. In severe cases of anterograde amnesia, people become unable to form new memories for facts or experiences. They can hold information in short-term memory but are unable to effectively transfer that information to long-term memory. For example, a viral infection damaged memory formation areas of the brain in British conductor Clive Wearing. He developed anterograde amnesia, making him unable to remember anything for more than a few seconds. Following the infection, he could not recognize entries he'd written in his diary minutes before. He could still recognize his wife but could not remember his wedding. Wearing also developed retrograde amnesia, causing him to lose access to earlier memories. He knew he was a music conductor but had no memory of ever having conducted a concert. He could not recognize musical scores but could play them effortlessly on the piano. Wearing did not forget how to play piano, because implicit memory (particularly procedural memory) is typically spared in anterograde amnesia. Amnesia patients often can learn new skills (such as riding a bicycle or programming a computer). They also often show priming effects, in which their behavior is shaped by experiences of which they have no memory. In anterograde amnesia, memories cannot be recovered because they have not been stored. In some cases, however, people may heal from injuries or diseases and regain the ability to store memories.
Psychoanalytic theories emphasize the power of unconscious information and desires. According to these theories, repression is a mental process in which people remove unwanted thoughts and memories from conscious awareness. The role of the psychotherapist is to bring these memories to consciousness so that they can be resolved. Unfortunately, the techniques used to recover memories, such as hypnosis and coached interviewing, can sometimes foster the creation of false memories. Research has compared abuse memories in people who never forgot the abuse, people who spontaneously remembered it outside of therapy, and people who remembered abuse only after therapeutic interventions. The results showed that memories recovered in therapy were rarely corroborated by objective evidence. Spontaneously recovered memories of abuse were corroborated by objective evidence at the same rate as memories of abuse reported by people who never forgot their abuse.
Researchers have demonstrated the ability to implant false memories of events that never occurred. These implanted memories differ from true memories in several regards. Namely, implanted memories are recalled in less detail than true memories and are recalled with less confidence. In 1995, American researchers Elizabeth Loftus and Jacqueline Pickrell reported implanting false memories of having been lost in a shopping mall as a child in 24 adults. During the first interview after the false memory manipulation, only 29 percent of participants "remembered" the false event. Over the course of two interviews, 75 percent resisted the suggestion that they had been lost in a mall as children. The small minority who "remembered" the false events used fewer words to describe them than they did when describing true events that actually happened to them. Their ratings for the clarity of memories and their confidence in them was lower for false memories than for true memories. Researchers have found similar results across studies in which they implanted false memories of participants taking hot-air balloon rides as children or having an encounter with the police.
Some individuals may be more prone to suggestibility than others. This has significant implications for eyewitness testimony. In fact, faulty eyewitness memory turned out to be a contributing factor in more than 75% of the first 250 convictions overturned using DNA evidence. For this reason, certain vital procedures must be followed to reduce eyewitness error. Eyewitnesses should not be shown a photograph of a sole individual and asked whether that individual is the perpetrator. Instead, they should be asked whether the perpetrator appears in an array of photographs of similar-looking individuals.
Poor police interviewing techniques also can contaminate memories and make eyewitness testimony unreliable. Police interviews often include "bait questions"—questions that mislead people into believing that certain evidence exists when it does not. When people are asked these kinds of misleading questions, their memory is significantly less accurate. The effect occurs even when people are warned in advance that some questions may be misleading.
An interview technique called the cognitive interview has been shown to improve the accuracy of eyewitness testimony. It involves four steps:
- Reinstate the context: Eyewitnesses are asked to think about what the surrounding environment looked like and how they felt during the incident.
- Report everything: Eyewitnesses are asked to report everything that comes to mind, even things they think may not be important.
- Recall the events in different orders: Eyewitnesses are asked to recall the event from beginning to end, in reverse order, and then starting with the part of the incident that left the strongest impression.
- Change perspectives: Eyewitnesses are asked to try to describe the incident from the perspectives of others present.