Study with the several resources on Docsity
Earn points by helping other students or get them with a premium plan
Prepare for your exams
Study with the several resources on Docsity
Earn points to download
Earn points by helping other students or get them with a premium plan
Research indicates that age-related increases in distorted memories are the result from impairments in memory encoding, retrieval and monitoring mechanisms that ...
Typology: Summaries
1 / 46
This page cannot be seen from the preview
Don't miss anything!
Bachelor Degree Project in Cognitive Neuroscience Basic level 22.5 ECTS Spring term 2018
Adam Hedin
Supervisor: Almira Thunström Examiner: Oskar MacGregor
Abstract
Our memory is prone to distortions which in everyday life can lead to mistaken memories. This thesis investigates memory distortion. In addition, one might recall (e.g. an event) correctly but misremember the source of the event (e.g. place or time of the event); this particular type of memory distortion is called source amnesia. Here, an overview of cognitive theories of memory distortion as well as the neuroscience behind memory distortion is provided. In addition, the particular memory distortion of source amnesia where one is unable to acquire when or where a fact was learned is further investigated. Results indicate that an overlap of qualities related to the information being learned causes information to be linked to wrong sources, thus creating distorted memories. Misinformation is also indicated to produce impairment in memory. In memory distortions, memory impairments are representative in various areas of the brain, including the hippocampus and the amygdala in the medial temporal lobes as well as in the frontal cortex and in the visual cortex. These key areas are also closely related to brain aging in Alzheimer´s disease and in schizophrenia, depression, posttraumatic stress disorder (PTSD) and in drug and alcohol abuse. Individuals inflicted with these disease symptoms seem to be more prone to source amnesia compared to controls. The limitations and future directions of what we can study regarding memory distortion and source amnesia are also presented in this thesis.
Keywords : memory distortion, source amnesia, misattribution, memory impairment
1. Introduction It can be stated that even though one can retrieve vivid events of the past, one is prone to do so in a manner of inaccuracy or distortion (Dennis, Bowman, & Turney, 2015). This faulty way of remembering is defined as memory distortion. In addition, one might recall (e.g. an event) correctly but misremember the source of the event (e.g. place or time of the event); this is called source amnesia.
Consequently, given this mismatch in memory, research highlights the difficulty to differentiate between true and distorted memories, making distorted memories a crucial and demanding area of interest within the field of memory research (Dennis et al., 2015). Memory distortion and in particular source amnesia is an interesting field of study as it helps neuroscientists to study the memory system. Memory distortions and source amnesia can both be a result of a cognitive damage and natural cognitive decline. There are several cognitive theories of why memory distortion occurs. While some theories focus on the social and cultural context in which we form and retrieve memories, (Johnson, Raye, Mitchell, & Ankudowich, 2012), others focus more on how our memory is distorted by external factors such as misinformation and contradictory information (Loftus, 2005). One of the most prominent theories, the Deese-Roediger-McDermott theory, focuses mainly on memory distortions that occur in laboratory settings. Subjects presented with word lists that contain related words such as juice, ham, egg, and pancake; will also recall a word that is not listed but related, such as toast, as the context of the words together forms a breakfast (Roediger & McDermott, 1995). Another aspect of memory distortion is source amnesia. Theories of source amnesia suggest that one can recall a fact without being able to remember where or when the information was originally experienced or acquired, which applies to both memories of facts and personal memories such as one’s childhood. These theories will be further elaborated on in this thesis. There are also many neurobiological and pathological causes to
memory distortion and source amnesia such as drugs, dementia, psychiatric illnesses, and old age, all which will be further described in this paper. The aim of this thesis is to investigate why our memories can be badly mistaken by answering the question:
Different models of memory distinguish between memories of shorter length, for example, sensory memory which contains a time-lapse of milliseconds to seconds. Memories that are of short to medium-lived persistence are defined as short-term, whereas working memory have a time-lapse of seconds to minutes and long-term memory which have a memory persistence of decades (Gazzaniga, Ivry, & Mangun, 2013).
2.1.2 Long-term memory Long-term memory refers to the concept of retaining information for a significant time (i.e. days, months and years). The long-term memory can be divided into two divisions due to differences in stored knowledge. The first is called declarative memory which deals with memory for general or personal facts and events that one has the conscious access to enable in the memory and thus, for instance can report verbally. This memory is also referred to as explicit memory. Declarative memory is divided into episodic memory and semantic memory. Episodic memories are personal autobiographical memories, we recall them as what, when, where and whom it happened with, this memory should not be mistaken for personal knowledge, e.g. knowledge of remembering the day of your birth, one does not remember the experience of that day. The episodic memory is the outcome of fast associative learning about a single episode that can be retrieved from our memory (Gazzaniga, Ivry, & Mangun, 2013).
The semantic memory is knowledge of objective character which is of a factual kind but does not indicate the situation of which it was learned, meaning, one might know a fact but he or she do not know where that specific fact was learned (e.g. telling time). Furthermore, we have nondeclarative memory also called implicit memory which cannot be verbally reported due to the knowledge not being consciously accessible, e.g. memory types as habituation, priming or conditioning. Finally, there is the procedural memory , a form of nondeclarative memory of which depends on repeated and extensive experience (e.g. how to read or swim) (Gazzaniga, Ivry, & Mangun, 2013).
2.1.3 Semantic and episodic memory Memory and its context concerning an event are often important to an individual. In order for an organism to successfully adapt to its environment, it must retain some information concerning acquired knowledge so that future actions can be modified or elicited
appropriately. If one is able to recollect contextual details of previous experiences one is also setting the foundation of forming an important distinction between semantic memory and episodic memory (Tulving, 1983). According to Tulving (1983), the semantic memory is our general knowledge of the world e.g. rules, meanings, and factual details. We, for instance, know that Paris is the capital of France and that 7 x 6 = 42. These types of knowledge are useful even though we cannot usually remember when and where we learned them. The episodic memory, in contrast, is the recollection of personally-experienced events. This type of memory includes knowledge about something that has occurred and also some recollection of the time and place of what has occurred. If one has to recollect for instance the memory of a car crash, contextual details of the place, time, and sequence are of great importance (Tulving, 1983).
2.2 Memory and diagnostic tests Several diagnostic tests could be used in order to test prefrontal function and source memory function in participants with source amnesia; some of them are explained next.
2.2.1 The verbal fluency test In the verbal fluency test which is a short test of verbal functioning two tasks is typically consisted (Shao, Janse, Visser, & Meyer, 2014). One task tests category fluency and one letter fluency (sometimes called phonemic fluency). Participants have one minute to produce as many unique words as possible within a semantic category (category fluency) or starting with a given letter (letter fluency) in the standard versions of the task. In each task, the participant's score is the number of unique correct words. Verbal fluency tasks are often included in clinical practice, neuropsychological assessment and in research. The verbal fluency tasks have for instance been used to support diagnoses of attention- deficit/hyperactivity disorder and in cognitive impairment in persons who have neurodegenerative diseases, such as Parkinson’s disease or Alzheimer's disease (Shao, Janse,
order to measure different cognitive functions, for instance executive processes, mediated by the frontal lobe (Adleman et al., 2002).
3. Memory distortion Sometimes our memory is incorrect; this is called memory distortion (Schacter, & Slotnick, 2004). Memory distortion can inter alia be explained through misattribution and suggestibility. Misattribution is the result of retrieved information being linked to the wrong source (e.g. having a previously imagined event, mistaking it for a real event). In suggestibility (e.g. misleading questions) one incorporates wrong information from external sources (Schacter, & Slotnick, 2004). Additionally in one specific type of memory distortion called source amnesia, one can remember a few facts but not where or when those facts have been learned; this is a concept that will be further explained next, after a presentation of cognitive theories of memory distortion and the neuroscience of memory distortion.
3.1 Cognitive theories of memory distortion Memory distortions are errors and misinterpretation of memories (Johnson et al., 2012). In addition, memory distortion is a phrase used for several types of errors in the encoding and retrieving of short or long-term memories (Johnson et al., 2012). There is a wide diversity when it comes to memory distortions; some appear in everyday life, some of in controlled laboratory tasks, others in traumatic life events, which can lead to legal consequences (Brainerd & Reyna, 2002). For the sake of simplicity one possible solution to better understand memory distortion is to investigate theories of which are most widely studied in relation to distorted memories (Brainerd, & Reyna, 2018).
3.1.1 The source monitoring framework The source monitoring framework proposes that memories (remembering) are attributions to on-going mental experiences such as one’s subjective aspects, beliefs, prior
knowledge, social context, goals and motives, features of which can be composed together during a specific event (Johnson et al., 2012). Mental experiences can be divided into perceptual information (e.g. sound, colour) contextual information (e.g. temporal and spatial characteristics), emotion, semantic concepts, cognitive activities (e.g. imaging, retrieving added information) as well as recency and familiarity which are less specific qualities. All qualities judge the root of the mental experience due to the fact that different sources differ on dimensions (e.g. we ought to have very strange content in dreams compared to real life). The overlap of qualities from different sources creates misattribution, for instance, one having a specific vivid imagination from the past, claiming it to be a previous perception (Johnson et al., 2012). The outcome of a source monitoring process is labelled memory attribution , a process of which collects evidence from different mental experiences. The amount of information which the process considers depends on e.g. past experience, motives, and task content. Furthermore, our cognitive system can work in systematic processes of which enable the possibility to retrieve extra information, examining plausibility with given knowledge and how consistent a memory is in a narrative. The processes function as a correcting system which creates doubt about clear but doubtful memories or about believable but faulty memories (Johnson et al., 2012).
Doubt can be very practical in that it assists in further efforts to seek proof, to remember, plant judgment, or enabling the option to live in uncertainty. Source monitoring processes are affected by beliefs (e.g. the quality of a memory source), knowledge and an evaluation and consultation about a social/cultural context in memories. The social and cultural context is proposed as the deciding mechanism behind what we remember and how often we do so, as well as what we consider good evidence in recalling an event (Johnson et al., 2012).
Loftus (2005) proposes a series of questions in order to understand the misinformation paradigm. The first question states under which conditions people are susceptible to misinformation and its negative impact. Theories stipulate that people are more prone to having their memories affected when misinformation is introduced after the time passage has managed the original event memory to fade (Loftus et al., 1978). As earlier mentioned in the passage of time, the memory of the event is weakened, and thus, there is a limited chance that the individual notice a difference while the misinformation is being processed. With very long intervals between an event and after misinformation, the memory of the event might be so weak that it is as if it has not even been presented. Consequently, there would be no difference and detection between the misinformation and the original memory meaning the subject might easily accept the misinformation (Loftus, 2005). In addition, to temporarily change someone´s state can increase the effect of misinformation e.g. individuals are more susceptible if they are led to believe that they, for instance, have been drinking alcohol (Assefi & Garry, 2003). Susceptibility is also greater in those who are hypnotized, (Scoboria, Mazzoni, Kirsch, & Milling, 2002).
3.1.3 Confabulation and delusion Confabulation is a term often used to describe amnesia patient’s production of false memories, whereas delusion can be defined as false beliefs of which conditions suffer in psychiatric cases e.g. schizophrenia, or in some cases people who suffer from neurological damage (Turner & Coltheart, 2010). Patients suffering from these conditions can vary greatly in the claims they make. A patient who is confabulating might claim that he is a hospital porter when the fact is that he is treated for brain injury as an inpatient of the hospital. If a patient suffers from e.g. Capgras delusion he might claim that an identical imposter has replaced his wife. Furthermore, there are patients with delusions of control, who might claim that an outside force is controlling their actions. Confabulations and delusions might be very
different but still, they share several characteristics. The term delusion is usually used to describe false beliefs that are: consistent over time, farfetched or bizarre and held with conviction. Confabulation, however, is argued to not meet these criteria’s, thus one should be treating the term separately from delusion (Turner & Coltheart, 2010). According to Fotopoulou, Conway and Solms (2007), confabulation can be defined as the production of distorted, misinterpreted or fabricated memories concerning oneself or the world. This is done without the conscious intention to deceive. Furthermore, serious misattributions can occur and thus create confabulation if the frontal cortex (ventromedial prefrontal cortex in particular) gets damaged (Damasio et al., 1985; Johnson, 1990; Johnson et al., 2000; Moscovitch, 1995; Schnider, 2008). In a study, Mercer, Wapner, Gardner, & Benson, (1977) examined if confabulation can reflect a patient’s suggestibility. The patients were made to believe that they previously had given a response concerning some questions of which they, in fact, had answered ―I don’t know‖, they were then asked to reproduce their answer. Mild and severe confabulators both generally stood by their previous answer of ―I don’t know‖ and there was no inclination of answering the questions concerned.
3.1.4 The Deese-Roediger-McDermott Paradigm In the Deese-Roediger-McDermott (DRM) task, lists of words which associate with one another (e.g., hospital, nurse) are presented to subjects (Pardilla-Delgado & Payne, 2017). After sufficient time has passed, the participants are asked to recognize or recall the words from the list. Furthermore, participants are asked in the recognition memory version of the DRM task if they remember the words which were presented in the list as well as related words (which were not presented) e.g. critical lure words (e.g. doctor, a word related to hospital and nurse). The critical word is usually identified by the subject with high confidence (Pardilla-Delgado & Payne, 2017). According to Pardilla-Delgado & Payne (2017) the delay
Furthermore, Gallo (2010) implies that the theoretical process that is the cause of the DRM illusion can be divided into a framework of activation and monitoring. It can be stated that the part of activation is explaining processes of which can mentally activate for instance bait or the retrieval of information of what might be false information. The phenomena of monitoring explain the process of decision and any memory editing that can assist in determining the foundation of information of which is activated. By activation, wrong memories do enhance, whereas in monitoring memories are suggested to be reduced (Gallo, 2010).
3.1.5 Fuzzy-trace theory The fuzzy-trace theory (FTT) does not solely focus on memory, rather it is an interdisciplinary model of cognition. The theory is interdisciplinary in the sense that it rests on two different factors. The first factor argues that FTT is not enclosed to memory alone; the theory also concerns the ability of higher reasoning. The goal is to integrate theories and conclusions within the domains of memory and reasoning by examining the relationship between these two domains of study (Brainerd & Reyna, 2004). According to Brainerd & Reyna, (1990); Reyna & Brainerd, (1991), FTT started as a model of reasoning of which was driven by two questions. The first question was concerning the relationship between representational processes in psycholinguistics. The second question involved children’s ability to solve logical problems in which reasoning was used in relation to the children’s ability to recall the background information of which enabled a solution to the concerned problem (Brainerd & Kingma, 1985).The other factor concerning FTT and its interdisciplinary character is the fact that FTT focuses on developmental and non- developmental work (Brainerd & Reyna, 2004). Within the theory of FTT, the goal is to integrate three essential approaches to cognition: mainstream cognitive psychology (studies of normal adults), mainstream cognitive development (developmental studies), and studies of
mainstream neuropsychology (brain mechanisms) (Brainerd & Reyna, 2004). FTT has concerning true and wrong memory reports integrated these approaches by initially doing several developmental studies which evolved into adult experimentation to furthermore continue into investigations of neurophysiological character (Brainerd & Reyna, 2004).
Brainerd & Reyna, (2004) continues to describe the explanatory principles of FTT. There are two approaches to memory development in relation to FTT. First, the explanation of memory development can be described by how information is represented in memory followed by how these representations later are retrieved and preserved. FTT makes a distinct difference between representations of which apprehend the surface of an experience and representations of which apprehend the gist of an experience. Secondly, the focus lies on securing tests of which are strong, this is done by generating new predictions concerning memory development, in particular, predictions of which are counterintuitive (Brainerd & Reyna, 2004).
The human brain enables a distinction between verbatim and gist traces of experiences. Verbatim traces are representations of which are integrated of a memory targets surface, also associated with item-specific information such as contextual cues (Brainerd & Reyna, 2004). Traces that are of verbatim character are shallow but accurate representations which can be forgotten quickly (Reyna, 2012). On the other hand, gist traces represents elaborative information about a memory target such as semantic and relational information, the essential meaning of the situation (Reyna, 2012). Together, representations of gist and verbatim are formed in parallel, representing a variety of qualities of a stimulus. In order to make accurate calculations for instance; adding numbers, using logic or computing probability, one is acquired to use the representations of verbatim. It is assumed that people rather work with gist-based representations due to verbatim representations being more difficult to work with (Reyna, 2012).
3.2.1 The medial temporal lobe The medial temporal lobe is often implicated in memory distortion or dementia, hippocampus in particular, due to it being affected in amnesia (bilateral hippocampal damage is often present in amnesia patients) (e.g., Eichenbaum & Cohen, 2001; Milner, Squire, & Kandel, 1998). The anterior hippocampus is associated with the binding of memory (Johnson et al., 2012). According to Addis, Moscovitch, Crawley, & McAndrews (2004), hippocampal activity during the remembering of autobiographical events has a positive correlation to rated memories for details, which is essential for avoiding grave source amnesia. Dysfunctions of the medial temporal lobe are highly implicated as a key area associated with memory distortion and source amnesia (Addis, Moscovitch, Crawley, & McAndrews, 2004).
Gonsalves et al. (2004) were able to look at brain activity through fMRI when subjects saw pictures and when they had to imagine pictures. They were then asked to recall images, and categorise them according to ―seen‖ or ―imagined‖. The results indicated that greater activity could be found in the precuneus (PCu) for items of which were imagined that participants falsely reported to have ―seen‖ than for those that they correctly reported being ―imagined‖. Distorted memories have a tendency to have less detail compared to memories that are true (Gonsalves et al., 2004). Numerous neuroimaging studies indicate that there is less activity for wrong compared to true memories in areas of which represent the encoding and retrieval of perceptual detail (e.g., Mather, Henkel, & Johnson, 1997; Norman & Schacter, 1997; Schooler, Gerhard, & Loftus, 1986).
Cabeza, Rao, Wagner, Mayer, & Schacter (2001) made a study that investigated types of memory traces recovered by the medial temporal lobe; neural activity during authentic and illusory recognition was measured with fMRI. 12 healthy adults watched a segment of a videotape in which two narrators alternated presenting lists of associated words, then the subjects performed a recognition test including words presented in the study lists,
called true items , new words in close relation to the studied words, called wrong items , and new unrelated words, called new items. The result showed that activity in the regions of the anterior medial temporal lobe did not distinguish true from false, whereas activity in the posterior medial temporal lobe regions did. This suggests that there is a specific subconscious mechanism for true and wrong memories (Cabeza, Rao, Wagner, Mayer, & Schacter, 2001).
3.2.2 The amygdala The amygdala, a part of the limbic system located in the medial temporal lobe near the hippocampus is representing the process of emotion (LeDoux, 2000). It is suggested that during encoding in participants of which are healthy, the activity of the amygdala is greater for emotional cues compared to cues which are neutral e.g. (Cahill et al., 1996). In addition, greater activity in the amygdala can be shown during encoding for remembered compared to emotional items of which are forgotten (Dolcos, LaBar, & Cabeza, 2004).
3.2.3 The frontal cortex Serious misattributions can occur and thus create confabulation if areas in the frontal cortex (ventromedial prefrontal cortex in particular) - are damaged either through trauma or neurodegeneration (Damasio, Graff-Radford, Eslinger, Damasio, & Kassell, 1985; Johnson, 1990 ; Johnson, Hayes, D’Esposito, & Raye, 2000; Moscovitch, 1995; Schnider, 2008).
3.2.4 The visual cortex In regions associated with visual processing, a greater local activity was attributed to true memories compared to subsequent false memories, thus indicating that visual processing is important in the encoding and retrieval of true memories (Baym & Gonsalves, 2010). Greater activity in the right frontal cortex and bilateral medial temporal lobe was on the other hand more indicated in both true and wrong memories compared to forgetting. The results presented by neuroimaging suggest that wrong memories need at least some information
