Chapter 8 Chapter Summary

Chapter Overview:

Chapter 8 focuses on the natural process of forgetting. While defining forgetting might initially appear to be an easy task, it is actually quite tricky (for example, is a memory completely gone or just momentarily unavailable, and how do you know?). Tulving suggested that forgetting is “the inability to recall something now that could be recalled on an earlier occasion” and Wixted expanded this definition to include the inability to access information that was successfully encoded and that could previously be retrieved by the same retrieval cue. In other words, forgetting focuses on a memory that is inaccessible not necessarily unavailable.

Daniel Schacter outlines seven different ways that memory can fail in the seven sins of memory. There are the three sins of omission where the memory is unavailable: transience, absent-mindedness, and blocking. And the four sins of commission where the memory is distorted: misattribution, suggestibility, bias, and persistence.

Amazingly, Ebbinghaus’ forgetting curve, proposed in 1885, still holds true today. This curve shows that most forgetting occurs soon after learning and then levels off. It is likely that the steep drop in forgetting reflects learning that is never consolidated, and the slower loss of information reflects the loss of consolidated memories. Therefore, disrupting consolidation is a source of forgetting. Consolidation may be disrupted by engaging in effortful cognitive activity shortly after learning and/or learning information that is sufficiently like older, unconsolidated memories.

Two early theories of forgetting consolidated memories are decay and interference. Decay theory suggests that memories simply vanish over time, but it was too difficult to test to gain popularity. Interference theories have been more popular with McGeoch’s (1932) model, one of the earliest. He proposed two types of interference: proactive and retroactive. McGeoch used the results from paired-associated experiments to propose his three-factor theory of forgetting where forgetting was the result of response competition, altered stimulus conditions, and set. Response competition occurs when more than one item is retrieved, and the correct response is unknown. Altered stimulus conditions occurs when the context during encoding and retrieval are different enough to negatively affect recall. Set or mental set (similar to bias) occurs when the context of the situation makes you recall the wrong set of information (thus preventing accurate recall). Newer neurological research suggests that decay might also be a cause of forgetting.

Explicit memory probably evolved to help organisms adapt to more complex environments so that they can learn from their experiences. However, because they will not know what elements of an event are important, they engage in promiscuous encoding. In other words, all elements of every event are encoding and, as a result, need a dedicated mechanism for forgetting else our memory systems could become overwhelmed.

The spatial-contextual elements of episodic memories that are housed in the hippocampus are recorded in distinct neural codes for separate episodic memories through a process called pattern separation. As a result, interference cannot account for the forgetting of hippocampal memories. Instead, neurogenesis (the growth of new neurons) and the loss of receptors cause forgetting in the hippocampus. Neurogenesis causes changes in the hippocampus that include altering the strength of existing connections. As a result, previously effective retrieval cues no longer work and forgetting may occur. This process is known as neurogenesis-dependent decay and provides evidence of the decay theory of forgetting.

Support for neurogenesis-dependent decay comes from research (both animal models and human) on infantile amnesia – the inability for adults to remember events from early childhood. Infantile amnesia has four interesting features in humans: it affects episodic memories but not semantic or implicit memories; there is no abrupt transition from having no memories to having memories; older children remember things longer than younger children; and it is not unique to humans. Infantile amnesia is most dense during the time when neurogenesis is at its peak (prior to three years old). During the ages of four to seven, more memories are recalled than at younger ages but not as many as in older childhood – at this point neurogenesis is still higher than in adults but is decreasing.

Of course, not all memories decay; some are strengthened by a process called memory-trace consolidation which occurs during retrieval or through sleep. Memory-trace consolidation is the strengthening of a memory’s neural connection promoted by frequent activation. These memories are less vulnerable to neurogenesis-dependent decay.

Another benefit of frequent activation or retrieval of hippocampal memories is the production of a protein necessary to keep the neuron’s potentiation (the ability to fire). Without activation, receptors may be lost leading to rapid forgetting as seen in Ebbinghaus’ forgetting curve. This forgetting, also caused by decay, occurs several weeks before neurogenesis-dependent decay can begin.

More permanent, consolidated memories, however, do not seem to decay. With these memories, based in the neocortex, the main cause of forgetting appears to be interference.

Another type of forgetting is called retrieval-induced forgetting. In RIF, participants use a paired-associate task where they practice recalling items from a category. Recall is then compared for the practiced items, unpracticed items from the same category, and unpracticed items from a different category. Not surprisingly, recall of the practiced items was superior. However, recall of items not practiced but from the same category was the worse. Various explanations have been suggested. Competition-induced interference proposes that when retrieving the practiced item, participants suppress other items in the category thereby causing difficulty in recalling them later. However, recent research suggests that a mismatch in mental contexts is a better explanation for RIF. That is, the cognitive processes of studying and retrieval create mental contexts that serve as retrieval cues. So, when items from the previously-retrieved categories are being recalled, the mental context of retrieval is evoked. But this context is not a helpful retrieval cue for items that have not been previously retrieved. For the items from a category that were never retrieved, only the study phase of mental context is evoked, and as a result, there is no disadvantage.

All of the forgetting discussed so far has been incidental forgetting. However, sometimes we purposely try to forget; in other words, we engage in motivated forgetting. A popular method of studying intentional forgetting is the list-method directed-forgetting (DF) paradigm. Here participants are presented a list of words and told to either remember them or forget them. They are then presented with a second list of words to remember. Two consistent findings emerge: there is a cost of forgetting, where fewer items recalled in the forget condition; and there is a benefit of forgetting, where those that were supposed to forget list 1 items, recalled more items from list 2, which demonstrates a two-factor model of directed forgetting. Stopping rehearsing list 1 creates a change in mental context that results in the cost of forgetting. However, ending the rehearsal for list 1 reduces proactive interference for list 2 and increases better strategies and produces the benefits of forgetting. Neuroscience research supports this model.

When we want to forget memories of personal experiences, the research suggests a few strategies: we can suppress encoding the memory, we can change the context, we can suppress retrieval, and we can substitute our thoughts. 

Learning Objectives:

Having read this chapter, you will be able to do the following:

1. List the seven sins of memory.
2. Recite John Wixted’s definition of forgetting.
3. Describe the forgetting curve.
4. Describe the components of McGeoch’s three-factor theory of forgetting.
5. Explain how a paired-associate paradigm can be used to study proactive and retroactive interference.
6. Explain why an organism may engage in promiscuous encoding.
7. Describe the two components of an explicit memory and the regions of the brain associated with each component.
8. Compare and contrast forgetting processes in the hippocampus and the neocortex.
9. Describe infantile amnesia and provide an explanation for this phenomenon.
10. Compare and contrast three different explanations of retrieval-induced forgetting.
11. Compare and contrast incidental forgetting and motivated forgetting.
12. Describe the item-method and the list-method directed-forgetting (DF) paradigms.
13. Describe evidence that demonstrates that changes in mental context provide the best explanation for costs and benefits of forgetting observed in list method DF paradigm experiments.
14. Describe four different ways that people can achieve intentional forgetting.