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Source monitoring is an unconscious psychological assessment (attribution) humans perform to determine whether the origins of one’s memory, knowledge, or beliefs are real, and from a credible source. In summary, monitoring what is real. Individuals often attribute mental experiences to something dreamed, imagined or perceived. Individuals utilize different sources to establish the basis of their memory or knowledge. Habitually, people use configural information and facial recognition to recognize other people, a processing system of faces in the brain known as a “sum of parts” perception. This aids individuals to recognize a childhood friend as a real individual, not a character from a novel. Linguistic and categorical information is utilized as well. Source monitoring is divided into external source monitoring and internal source monitoring.

Source memory
The concept of source memory overlays with the knowledge of memory for context. Source memory refers to the recalling of the source of learned information such as knowledge of when or where something was learned. Often, memories are triggered by contextual information (i.e. time and place). A failure in source memory can be associated with aging, stress, intoxication, or distractibility, which is a phenomenon where an individual acquires fragments of memory without the recollection of how or when the fragment of memory was attained.

Types of source monitoring

 * External source monitoring focuses on sources which are part of the environment of a person.
 * Internal source monitoring is based on the internal factors of the environment. Internal source monitoring judges between two simultaneous but different ideas of a person. For example: internal source monitoring would take place if someone says something out loud but thinks something else at the same time.
 * Reality monitoring is also called internal-external monitoring. It is the fusion and the contrast between internal thoughts and imaginings from memories and external events. In short, it is a cognitive process which processes the events of one’s life. An example would be discriminating a car accident portrayed in real life and in a newspaper.

Source monitoring framework
The source-monitoring framework is based on to the reality-monitoring but more elaborated by considering internal source monitoring and external source monitoring too. With this elaboration the source-monitoring framework explains how the differentiation of different sources works.

The different types of source monitoring are all based on the memory characteristics like perceptual or cognitive operational information and the judgement process. The memory is not tagged with the source but it can be determined by considering memory characteristics like:


 * perceptual information
 * contextual information
 * semantic detail
 * affective information
 * cognitive operational information

If the memory has a lot of information about the cognitive operations, it indicates being derived from an internal source. The other four characteristics indicate the memory orginating from an external source. The way people judge the memory can also support source monitoring. It can be classified in two ways:


 * 1) The judgment can proceed automatically as heuristic judgements and is often based on a rule of thumb which indicates which source is more likely.
 * 2) The judgment could also proceed controlled as symstematic judgements for which a rule of thumb is not sufficient.

The heuristic judgement is more likely for source judgements, because its criteria is based on memory characteristics, while the systematic judgement deals with the criteria of the embeddedness of the memory like its plausibility and consistency with other memories. Both judgement types are susceptible to personal goals and motives. The different judgement types and the susceptibility of each also indicate that source attribution is flexible and varies under different circumstances.

Brain substrates
There are several areas involved in the encoding, remembering and retrieval of source memory. These include the medial temporal lobe, the prefrontal cortex, the parietal lobe and several other posterior brain areas.

Medial temporal lobe:
The hippocampus is a structure in the medial temporal lobe that is important in source memory, and memory in general. Activity is found to be greater in the hippocampus for items of which the corresponding source is correctly identified than for those whose source is incorrectly identified. These findings support the notion that the hippocampus contributes to binding features into complex episodic memories during encoding, as well as in remembering item-context information. During encoding, the hippocampus works together with the entorhinal cortex and other midbrain structures to bind, associate and integrate information acress space or time.

The hippocampus is activated for recollection of inter-item associations. When context is retrieved intentionally or unintentionally, the parahippocampal cortex is activated. The perirhinal cortex is involved when an item prompts the retrieval of an associatied item. The activity in the parahippocampal cortex is more similar to hippocampal activity than to perirhinal cortex activity, and reflects processing of spatial context. Another view on the parahippocampal activity is that it is involved in contextual information. Recent evidence also associates perirhinal/entorhinal cortex activity with visual source memory and parahippocampal cortex activity with auditory source memory.

During memory retrieval, fMRI signals in hippocampus and perirhinal cortex go in opposite directions when memory strengthens. Non-linearly, hippocampal activity increases whereas perirhinal activity decreases with memory strength. This contrasting activity impedes the mapping of different medial temporal lobe regions.

Prefrontal cortex:
Source memory judgements are associated with increased activity in the lateral prefrontal cortex. This includes increased activity in the superior, middle, and inferior frontal gyri. This activity has been correlated to multipe different types of source information, such as location, size and the cognitive operations that were performed. The increase in activity also corresponds to a wide range of materials, such as auditory and visual words and pictures. Increased activity in the left prefrontal cortex during encoding of source information predicts more accurate recognition and retrieval of this information at a later point in time. Furthermore, the left lateral prefrontal cortex contributes to remembering source information by systematic monitoring of specific information, while the right lateral prefrontal cortex is important for heuristic evaluation of information that is less differentiated, such as familiarity and recency in item recognition.

The ventrolateral prefrontal cortex contributes to control processes that are necessary to select and encode the appropriate and specific features of items, and this process enhances the representation of goal-relevant features of items during encoding. The dorsolateral prefrontal cortex contributes to more domain-general processes that support the organization and elaboration of multiple features in working memory, which are necessary for encoding associations between items for storage in long-term memory. This makes the dorsolateral prefrontal cortex in particular very important for the encoding and retrieval of source memory.

Accordingly, lesions of the frontal cortex disrupt processes that promote feature binding and that are involved in the revival and evaluation of source information. This damage often leads to certain deficits on source identification tasks.

Parietal cortex and other posterior brain areas
The accuracy of source memory relates to which specific features of a specific experience are encoded, how well those features are connected in memory and how they are accessed and retrieved during remembering. There is evidence for specifity based on categories in posterior visual areas for episodic memory. Examples from the fusiform cortex that are involved in encoding different types of materials and objects such as faces in the fusiform face area (FFA), scenes in the parahippocampal place area (PPA), and the visual word form area in the left occipito-temporal sulcus, which borders the fusiform gyrus.

In addition, activity in the left superior temporal gyrus is related to successful encoding of locations, and activity in the posterior inferior temporal cortex with encoding source information related to color. Moreover, for visual stimuli encoding activity in the right fusiform predicts correct and accurate source memory for perceptual details with high specificity, while activity in the left fusiform is related to judgements based on information that is less specific.

Emotion
Experienced emotions (e.g. arousal) enhance perceptual processing even on a low level, such as contrast sensitivity. Items of emotional information are better recognized compared to neutral ones. Memory of emotional events is often strongly vivid, because of the interaction between the hippocampus and the amygdala. This results in enhanced remembering of source information and higher confidence in doing so.

Regarding age-related differences in memory performance, the gap between younger and older adults is narrower for emotional events, compared to non-emotional events. For emotional contexts, memory relies on cognitive processes, that are preserved in older adults.

Age
Looking at age related differences in source monitoring, several studies show that older adults perform worse compared to younger adults. Evidence from cognitive-behavioral studies suggests, that older adults show memory binding deficits and memory source deficits, that are greater than item memory deficits. The impaired performance in source monitoring by older adults is further explained by studies showing, that they have difficulties in encoding perceptual cues.

The prefrontal cortex is affected by aging. This leads to a decline in cognitive function and might result in the inferior performance in source monitoring by older adults, compared to younger ones. Further studies suggest the importance of the hippocampus. With increasing age, the hippocampal activity is reduced in long-term memory tasks.

Schizophrenia
Patients with schizophrenia tend to have problems with source monitoring more often than healthy individuals. Studies have suggested that impairments are mainly visible in the inability to distinguish whether certain information was obtained from an internal or an external source, often causing patients to regard their own thoughts as being obtained from an external source. However, these deficits were found to have different associations to the different symptoms this illness includes. In general, positive symptoms are often positively related to source monitoring problems, while negative symptoms are often inversely related to source monitoring problems. Patients with schizophrenia also tend to be more confident in the false memories their source monitoring impairments generate than healthy patients.

Source amnesia
Source amnesia occurs when someone is incapable to recall the source of a certain information. A person will in this case remember a certain information but not where, when and from whom they learned about it. A person’s explicit memory is affected, whereas the implicit memory usually is not, because we forget factual knowledge and not unconscious memories. Furthermore, a theory for the occurrence of source amnesia is that a dissociation of the episodic and semantic memory leads to the lack of context, in which the information was learned.

The cause for this type of amnesia is believed to be insufficient memory encoding, which sounds very dangerous, but in fact is experienced by everyone sometimes. If a person does not recall a certain information for a long period of time it is possible to simply forget the source of it, but if this happens regularly it could be a symptom of a serious problem, such as a head trauma or schizophrenia. A head trauma could interfere with the functionality of the frontal lobe, which plays an important role in organizing, storing and linking memories to knowledge a person already attained. Patients who suffer from schizophrenia are very likely to suffer from restrictions in their episodic memory, which is responsible for recalling situations you actually encountered in the past, so also very important in recalling the source of a certain information you have. In contrast, semantic memory is not as affected as episodic memory, which explains why patients are able to recover certain information and facts without actually knowing where they learned those.

The consequences of source amnesia can be observed regularly and can be dangerous as misinformation has the potential to spread. Critical thinking and questioning the reliability of a source became more important than ever as information can propagate quickly and unchecked through social media. Additionally, oneself can be the target of source amnesia as it is possible that while writing a paper or an assignment a certain sentence from a textbook or an article pops up in your mind, which feels as if you just came up with it by yourself. If you include those sentences in your paper this is a form of plagiarism, even though you thought you initially came up with a certain phrase.

Certainly, these can also be consequences of a source monitoring error, but the major difference here is the misattribution of a source, so where you encountered the information first, and not a complete lack of the source as it is the case in source amnesia. Nevertheless, it is also possible that source amnesia makes a person sensitive to the misattribution of a source, which in turn transforms it into a source monitoring error.

Memory distrust syndrome
The concept of the memory distrust syndrome (MDS) was first introduced by Gudjonsson and MacKeith and since its’ introduction has been integrated into many scientific articles and books. The duo investigated this concept in the context of false confessions during police interrogation. The MDS was defined as “A condition where people develop profound distrust of their memory recollections, as a result of which they are particularly susceptible to relying on external cues and suggestions”. It can be triggered or intensified by different external factors, such as social isolation, persuasive interrogation and high emotional intensity. These cues are most likely fulfilled during police interrogation and have already led to false confessions in the past.

The main difference between source amnesia and the MDS is that in source amnesia you cannot recall the source of your information at all and in the case of a MDS you can recall your knowledge, but you certainly do not believe it is true.

Source monitoring error
Source monitoring error is a form of a memory failure in which information is remembered but the source of that information is falsely associated. While the semantic part of a memory endures, episodic contents, like the time and the place in which that memory was encoded, get mistaken. For example, it may be the case that an individual hears a joke from a friend or family member and later goes on telling the same joke to someone else, or maybe even the same person, being sure to have come up with that joke for oneself.

A source monitoring error can also be seen in the Deese-Roediger-McDermott (DRM) paradigm. Here, people get presented lists of word which they are supposed to learn. Each list contains words belonging to the same implicit theme. A list with the theme "sleep" for example could contain words like "bed", "pillow", "alarm", "night", "mattress" or "dream" but it is important to note that it would not contain the theme word "sleep" itself. Studies showed that participants who learned such a list of words were later on able to correctly identify or reject words that either were or were not in the original list but also often claimed to recognize the implicit theme as a word from the original list. An explanation for this phenomenon by means of source monitoring error is that while learning such a list of words people start thinking about the theme and create a memory of that. Later they identify that word as one they encountered on the list rather than as an object of their own thoughts.

The part of the brain that is most strongly related to source monitoring errors is the frontal cortex. Controlling of what information gets stored as episodic and semantic memory, producing metamemory and connecting information about the context to event memory the frontal cortex plays a big role in encoding what happened and when and where it happened. Interference at that point can cause to weaken the connection between the semantic and the episodic part of a memory. Accordingly, damage to the frontal lobes has been shown to increase source monitoring errors.

Older people as well as people with schizophrenia are more likely to make source monitoring errors than younger or healthy people. While for older people deficits in attentional control processes appear to be the reason, frontal dysfunction seems not to be the cause of increased source monitoring error in people with schizophrenia. In the latter, there seems to be a relation to hostility and studies showed that a lower IQ may also play a role.

False memories and related phenomena
Some phenomena challenge our source discrimination and the reliability of our memory. This stands for memory distortion and false memory paradigm that concerns memory reliability. This phenomenon explains the process by which a person fulfills a memory with antecedents that did not occur or changes the events different from what initially occurred. This process occurs when a person is not able to recall actual events from memory, giving erroneous sources that are accessible to them and serve to fill gaps to rely on, defined as false recognition. Memory distortion points to human brain nature and not necessarily flaws of cognitive impairment.

Memory distortion arises from adaptive processes, at which schemas are used for remembering more efficiently but causing distortions. Four domains play a role at distorted memories:


 * Imagination inflation: when novelistic events that are imagined, lead to overconfidence and misattribute memories, therefore, inducing imaginable false memories. This phenomenon is explained by reality monitoring errors; imaginated event(s) are more likely to be confused with memory if these unreal events share perceptual or conceptual cues of real events.
 * Gist-based errors: memory has limited storage at which numerous details are not stored in memory to be more efficient. This lack of details is associated with false recognition.
 * Contextual association: process by which the brain has the ability to rapidly predict outcomes of situations, leading to rely on focused-predicted memories, giving a base of representation to memories.
 * Post-event misinformation: paradigm describes the impairment of memory retrieval when misinformation is presented, creating a misinformation effect misleading the source of information.

Memory (mis)attributions
Within the source monitoring framework, memory attributions are based on information about for example where and how the mental experience was acquired. These informational cues are taken as evidence that the mental experience is a true memory. Memory attributions are strongly influenced by the quality of the mental experience, how much the mental experience is consistent with own knowledge and beliefs, and also by the consistency with reports of others about the same event. The construction of memory attributions depends on flexible criteria. These criteria vary in every situation and set the amount of evidence that is needed. Environmental factors as well as own motivations, goals and beliefs influence what information about the mental experience is looked for, how consistent the mental experience has to be and which criteria are applied.

Misattributions can occur when people recognize information but not its source. As soon as people realize that they might be confused about the information of a mental experience, they change their flexible criteria to stay consistent with their own beliefs and reports of others about the same event.

Research methods
Measuring source monitoring can be useful in a large variety of settings, including scientific research, clinical settings (e.g. in Alzheimer's disease and Parkinson's disease) and the justice system (e.g. eyewitness testimonies).

Source monitoring can be measured using a source-monitoring task. In these tasks, subjects are asked if items (such as words, sentences or images) have either been presented previously by one of several sources or have not been presented before. Most studies use a two-source, three-response-alternative task, in which items are memorized from two sources, A and B. Subjects are then presented with items from these two sources in combination with new items. They have three response options: They can respond that a test item is old and came from Source A, that it is old and came from Source B, or that it is new. Several varieties of this technique are used to measure external as well as reality monitoring.

For testing external source monitoring, some examples of the different sources to be discriminated are words presented on different lists, words presented visually versus acoustically, words presented in front of different backgrounds, or pictures associated with different colors. In measuring reality monitoring, subjects can be asked to discriminate between actually perceived and imagined words or images of objects.

A problematic aspect of this type of memory test is that it combines memory for the item (is the item old or new?) and memory for the source (if the item is old, is it from source A or source B?), resulting in confounding between these two types of memory. In light of this issue, Kevin Murnene and Ute J. Bayen suggest that the technical characteristics and theoretical implications of these measures should be carefully considered before using them to measure source monitoring performance.