Reconstructing the Past
- Unlike a tape recorder or video camera, human memory is highly selective and is reconstructive: People add, delete, and change elements in ways that help them make sense of information and events. They often have source misattribution, the inability to distinguish information stored during an event from information added later. Even flashbulb memories, emotionally powerful memories that are particularly vivid, are often embellished or distorted and tend to become less accurate over time.
- Because memory is reconstructive, it is subject to confabulation, the confusion of imagined events with actual ones. Confabulation is more likely when people have thought about the imagined event many times ("imagination inflation"), the image of the event contains many details, the event is easy to imagine, and the focus of attention is on emotional reactions to the event.
Memory and the Power of Suggestion
- The reconstructive nature of memory makes memory vulnerable to suggestion. Eyewitness testimony is especially vulnerable to error when the suspect’s ethnicity differs from that of the witness, when leading questions are put to witnesses, or when the witnesses are given misleading information.
- Findings on memory help clarify the issues in the debate about whether children are capable of making up accounts of sexual abuse. Children, like adults, often remember the essential aspects of an event accurately. However, like adults, they can also be suggestible, especially when they are very young, are in emotionally charged situations that blur the line between fantasy and reality, are asked leading questions, or wish to please the interviewer or conform to what they believe other children have said.
In Pursuit of Memory
- The ability to remember depends in part on the type of performance called for. In tests of explicit memory (conscious recollection), recognition is usually better than recall. In tests of implicit memory, which is measured by indirect methods such as priming and the relearning method, past experiences may affect current thoughts or actions even when these experiences are not consciously and intentionally remembered.
- In information-processing models, memory involves the encoding, storage, and retrieval of information. In the three-box model, there are three interacting systems: sensory memory, short-term memory, and long-term memory. Some cognitive scientists prefer a parallel distributed processing (PDP) or connectionist model, which represents knowledge as connections among numerous interacting processing units, distributed in a vast network and all operating in parallel. But the three-box model continues to offer a convenient way to organize the major findings on memory.
Three Memory Systems
The Three-Box Model of Memory
- In the three-box model, incoming sensory information makes a brief stop in the sensory register, which momentarily retains it in the form of sensory images.
- Short-term memory (STM) retains new information for up to 30 seconds by most estimates (unless rehearsal takes place). It also provides us with a working memory for the processing of information retrieved from long-term memory for temporary use. The capacity of STM is extremely limited but can be extended if information is organized into larger units by chunking. Items that are meaningful, have an emotional impact, or link up to something already in long-term memory may enter long-term storage easily, with only a brief stay in STM.
- Long-term memory (LTM) contains an enormous amount of information that must be organized to make it manageable. For example, words (or the concepts they represent) seem to be organized by semantic categories. Many models of LTM represent its contents as a network of interrelated concepts. The way people use these networks depends on experience and education. Research on tip-of-the-tongue (TOT) states shows that words are also indexed in LTM in terms of sound and form.
Conceptual Grid in LTM
- Procedural memories ("knowing how") are memories for how to perform specific actions; declarative memories ("knowing that") are memories for abstract or representational knowledge. Declarative memories include semantic memories (general knowledge) and episodic memories (memories for personally experienced events.)
Types of LTM
- The three-box model is often invoked to explain the serial-position effect in memory, but although it can explain the primacy effect, it cannot explain why a recency effect sometimes occurs even when the model predicts it should not.
Serial Position Effect
The Biology of Memory
- Short-term memory involves temporary changes within neurons that alter their ability to release neurotransmitters, whereas long-term memory involves lasting structural changes in neurons and synapses. Long-term potentiation, an increase in the strength of synaptic responsiveness, seems to be an important mechanism of long-term memory. Neural changes associated with long-term potentiation take time to develop, which helps explain why long-term memories require a period of consolidation.
- Areas of the prefrontal cortex are especially active during short-term memory tasks. The hippocampus and adjacent areas play a critical role in the formation of long-term declarative memories. Other areas, such as the cerebellum, are crucial for the formation of procedural memories. Studies of patients with amnesia suggest that different brain systems are active during explicit and implicit memory tasks. The long-term storage of declarative memories probably takes place in cortical areas that were active during the original perception of the information or event. The various components of a memory are probably stored at different sites with all of these sites participating in the representation of the event as a whole.
- Hormones released by the adrenal glands during stress or emotional arousal, including epinephrine and some steroids, enhance memory. Epinephrine causes the level of glucose to rise in the bloodstream, and glucose may enhance memory directly or by altering the effects of neurotransmitters. But very high hormone levels can interfere with the retention of information: a moderate level is optimal for learning new tasks.
How We Remember
- In order to remember material well, we must encode it accurately in the first place. Some kinds of information, such as material in a college course, require effortful, as opposed to automatic, encoding. Rehearsal of information keeps it in short-term memory and increases the chances of long-term retention. Elaborative rehearsal is more likely to result in transfer to long-term memory than is maintenance rehearsal, and deep processing is usually a more effective retention strategy than shallow processing.
Impoverished Encoding
- Mnemonics can also enhance retention by promoting elaborative encoding and making material meaningful, but for ordinary memory tasks, complex memory tricks are often ineffective or even counterproductive.
Why We Forget
- Forgetting can occur for several reasons. Information in sensory and short-term memory appears to decay if it does not receive further processing.
Forgetting Curves
New information may "erase" old information in long-term memory. Proactive and retroactive interference may take place.
Retroactive Interference and Proactive Interference
Cue-dependent forgetting may occur when retrieval cues are inadequate. The most effective retrieval cues are those that were present at the time of the initial experience. A person’s mood or physical state may also act as a retrieval cue, evoking a state-dependent memory.
- Some lapses in memory may be due to psychogenic amnesia, the forgetting of disturbing or shocking events, but psychologists are divided about why this occurs. The psychodynamic explanation, repression, has met with skepticism among psychological scientists, who consider it vague and unverified. In cases involving claims of recovered memories of repressed events, courts have also become skeptical.
Autobiographical Memories
- Most people cannot recall any events from earlier than the third or fourth year of life. The reason for such childhood amnesia may be partly biological. Cognitive explanations include the lack of a sense of self until the age of 2 or 3, young children’s impoverished encoding of their experiences, their focus on routine rather than distinctive aspects of an experience, and their immature cognitive schemas.
- A person’s narrative "life story" organizes the events of his or her life and gives them meaning. Narratives change as people build up a store of episodic memories, and life stories are, to some degree, works of interpretation and imagination. These narratives are affected by gender and culture. The central themes of our stories can guide recall and influence our judgments of people and events. Older people remember more from adolescence and young adulthood than from midlife, a phenomenon known as the reminiscence bump.
