What Are the Basic Stages of Memory?
The most widely accepted model of memory is the modal memory model proposed by Atkinson and Shiffrin, also known as the information-processing model. In this model, memory is conceptualized as consisting of three distinct memory stores:

What Are the Different Memory Systems?
Researchers agree that memory is served by multiple systems; some psychologists focus on memory content as the basis for defining the different systems and others focus on the process of memory storage as the way to differentiate among systems. One such distinction in memory systems is between explicit and implicit memory. Explicit memory involves the effortful storage and retrieval of declarative information and takes two forms: episodic memory, which is our memories of our personal experiences, and semantic memory, which is our memories of facts and information. Implicit memory occurs without attention. Just as there are different types of explicit memory, there are also different types of implicit memory. Procedural memory, or motor memory, is the memory of how to do things, like riding a bike, making a sandwich, and other sorts of motor skills. Two other types of implicit memories are attitude formation and repetition priming.

How Is Information Represented in Long-Term Memory?
The process of memory is composed of three stages: encoding, storage, and retrieval. Information gets stored in memory based on its meaning. Craik and Lockhart's levels of processing model of memory demonstrates that information is encoded with more meaning when subjects engage in elaborative rehearsal, and as a result, the information is more easily retrieved than when subjects engage in maintenance rehearsal. One way in which meaning is determined is through schemas, hypothetical frameworks that help organize information about the world. Schemas play a role in memory storage and in memory retrieval: We are more likely to remember information consistent with a schema than information that is inconsistent. Meaning is also important in theories of memory organization based on networks of associations. Units of information or nodes are linked to one another based on their meaning. Activation of one node increases the likelihood that associated nodes will be activated. Thus exposure to a dog increases the likelihood that related nodes of different types of dogs or different types of pets will be activated. This process is called spreading activation.

What Brain Processes Are Involved in Memory?
The brain region that has been consistently identified as playing a critical role in memory is the medial temporal lobes. The structures in this region of the temporal lobes include the hippocampus, the amygdala, and the rhinal cortex. The case of H.M. highlights the critical role that the hippocampus plays, especially in the consolidation of memory. Data from brain imaging studies suggest that, while the hippocampus plays a role in consolidation, the actual memories are stored in the region of the brain associated with processing that information. For example, visual information is stored in cortical regions that are involved in visual processing, and there are hemispheric differences associated with the type of information being stored. In addition to consolidation, the hippocampus plays a role in spatial memory and special cells in the hippocampus, known as place cells, fire when an animal returns to a familiar environment. The frontal lobes play immensely important roles in many aspects of memory. Of particular interest is the fact that more effortful processing of information is associated with greater frontal activation. One suggestion is that the frontal lobes are involved in working memory and so are activated during both encoding and retrieval of information. Memory modulators are neurotransmitters that can either enhance or impair memory. Epinephrine is one neurotransmitter that has been shown to increase memory. This enhancement of memory appears to be related to the release of glucose that accompanies the increase in epinephrine levels and the associated increase in arousal. The final brain structure discussed in this section is the amygdala, which plays an important role in the memory of emotional material.

When Do People Forget?
Forgetting is simply defined as the inability to retrieve information from long-term memory. Most forgetting occurs because of interference, similar events, or experiences make it difficult for us to retrieve the information for which we are searching. One psychologist described interference as being similar to the process of finding a pearl in a bucket of white marbles. Sometimes our inability to retrieve long-term memories is only temporary, this is known as blocking. If you have ever experienced the tip-of-the-tongue phenomenon then you have experienced blocking. The shallow encoding of information, absentmindedness, leads to the forgetting of information because we have not paid enough attention to details. When an individual experiences memory problems as the result of brain injury, disease, or trauma, this is known as amnesia. Some individuals lose the ability to recall events or information that occurred in the past (retrograde amnesia). Others suffer from anterograde amnesia, the inability to store new memories. The case of H.M. discussed in this chapter is an example of someone with anterograde amnesia.

How Are Memories Distorted?
Our memories can be inaccurate for a number of reasons. Source misattributions happen when we misremember the circumstances involved with a memory. The false fame effect described in the chapter is an interesting example of source misattribution. Source misattribution is also involved in a phenomenon called cryptomnesia, which occurs when a person perceives the recovery of information from memory as being an original idea of their own. Plagiarism charges against musician George Harrison and writer Stephen Ambrose are examples of this phenomenon. Memory errors have significant consequences in the arena of eyewitness testimony, where misidentification can send an innocent person to jail or allow a guilty party to escape punishment. Errors in eyewitness testimony can occur when people have to identify someone from a different ethnic group. Because we have less exposure to members of other ethnic groups, we tend to lump them all together in one group and see them as looking all alike. Eyewitness testimony is also prone to error because our memories can be distorted by misinformation, this is known as suggestibility. Psychologist Elizabeth Loftus has done extensive work on this issue, and you should be familiar with her studies discussed in the chapter. Confabulation, the false recollection of episodic memory, can occur in cases of brain injury as individuals recall incorrect information and then try to provide a coherent story to fit the mistaken recollections. The authors also touch on the controversial topic of repressed memory in this section. This is a topic over which psychologists hold very different opinions, and it will probably be some time before consensus is reached on this issue.