Source amnesia is the inability to remember where, when or how previously learned information has been acquired, while retaining the factual knowledge. This branch of amnesia is associated with the malfunctioning of one's explicit memory. It is likely that the disconnect between having the knowledge and remembering the context in which the knowledge was acquired is due to a dissociation between semantic and episodic memoryTulving, E. (1972). Episodic and semantic memory. In E. Tulving and W. Donaldson (Eds.), Organization of Memory (pp. 381–403). New York: Academic Press. – an individual retains the semantic knowledge (the fact), but lacks the episodic knowledge to indicate the context in which the knowledge was gained.
Memory representations reflect the encoding processes during acquisition. Different types of acquisition processes (e.g.: reading, thinking, listening) and different types of events (e.g.: newspaper, thoughts, conversation) will produce mental depictions that perceptually differ from one another in the brain, making it harder to retrieve where information was learned when placed in a different context of retrieval. Source monitoring involves a systematic process of slow and deliberate thought of where information was originally learned. Source monitoring can be improved by using more retrieval cues, discovering and noting relations and extended reasoning.
Causes Source amnesia is not a rare phenomenon – everybody experiences it on a near daily basis as, for much of our knowledge, it is important to remember the knowledge itself, rather than its source. However, there are extreme examples of source amnesia caused by a variety of factors.
Frontal lobe damage Individuals with frontal lobe damage have deficits in temporal context memory; source memory can also exhibit deficits in those with frontal lobe damage. It appears that those with frontal lobe damage have difficulties with recency and other temporal judgements (e.g., placing events in the order they occurred), and as such they are unable to properly attribute their knowledge to appropriate sources (i.e., have source amnesia). Those individuals with frontal lobe damage have normal recall of facts, but they make significantly more errors in source memory than control subjects, with these effects becoming apparent as shortly as 5 minutes after the learning experience. Individuals with frontal lobe damage often mistakenly attribute the knowledge they have to some other source (e.g., they read it somewhere, saw it on TV, etc.) but rarely attribute it to having learned it over the course of the experiment. It appears that frontal lobe damage causes a disconnection between semantic and episodic memory – in that the individuals cannot associate the context in which they acquired the knowledge to the knowledge itself.
Age-related Elderly individuals have been shown to exhibit source amnesia. Compared to younger individuals, in experiments where the individuals are presented with obscure or even made up trivia facts, older people remember less information overall in both recall and recognition tasks and they often misattribute the source of their knowledge, at time periods of both long and short delays.
This effect is potentially due to the neuronal loss associated with aging occurring mainly in the frontal lobes.Haug, H., Barmwater, U., Eggers, R., Fischer, D., Kuhl, S. and Sass, N.L. (1983). Anatomical changes in aging brain: Morphometric analysis of the human prosencephalon. In J. Cervos-Navarro and H.I. Srakander (Eds.), Brain Aging: Neuropathology and Neuropharmacology, Vol 21 (pp. 1–12). New York: Raven Press.Woodruff, D.S. (1985). Arousal, sleep, and aging. In J.E. Birren and K.W. Schaie (Eds.), Handbook of the psychology of aging. New York: Van Nostrand Reinhold. It has been previously noticed that frontal lobe damage can cause source amnesia, so the loss of neurons in this area of the brain associated with aging may very well be the cause of the age-related source amnesia seen.
Alzheimer's disease Alzheimer's disease (AD), which is known to be associated with frontal lobe dysfunction, is implicated as a cause of source amnesia. In laboratory conditions, one study found source monitoring to be so poor that the AD participants were correctly performing source memory attributions at approximately chance. This lack of ability to attribute the source of memories is likely related to AD patients' deficits in reality monitoring. Reality monitoring, the process of distinguishing whether information originated from an external or an internal source, relies on judgement processes to examine the qualitative characteristics of the information in order to determine if the information was real or imagined. It appears that it is this process that is experiencing the dysfunction, which causes mild confabulation in some AD patients, as well as being related to the source amnesia experienced in some individuals with AD.
Schizophrenia Schizophrenia is associated with episodic memory deficits often characterized by a confusion of internal stimuli and real events. It appears that individuals with schizophrenia often display failures in monitoring/remembering the source of information, especially for self-generated items – that is, they display source amnesia. This is a stable trait in this disease – one experiment found that over a two-year period, an individual's rate of source attributing errors was maintained, despite fluctuations in medication status and the individual's symptoms. This effect is possibly due to the malformation of associations among aspects of an episode needed for remembering its source; one neuroimaging study found that individuals with schizophrenia had lower activation of areas associated with source memory.
Individuals with schizophrenia who display source memory deficits often do so due to reality-monitoring dysfunction, which is a contributing factor towards the hallucinations that characterize the disorder. One study found that schizophrenia patients were not only slower, but also less accurate, at tasks involving reality-monitoring. The hallucinations that characterize schizophrenia are a result of deficit in reality monitoring – they exhibit an inability to differentiate between internally and externally derived information. Overall, there is evidence of a relationship between source monitoring errors and the disorganized thinking that characterizes those who have schizophrenia in that there is a strong tendency for those people with hallucinations to attribute their internally generated events (i.e.: hallucinations and delusions) to an external source (e.g., the experimenter). That is, schizophrenia is characterized by failing to encode themselves as the source of the idea, compounded by attributing these ideas/beliefs to an external source, all of which leads to those individuals with schizophrenia exhibiting behaviours typical of those with source amnesia; they misattribute the source of their knowledge, ideas, or beliefs.
Post traumatic stress disorder Post traumatic stress disorder (PTSD) is characterized by intrusive, vivid recollections of the traumatic event and impoverished episodic memory for all other events. Those individuals with PTSD experience memory distortions caused by source amnesia, as well as false memory construction and unintentional integration of information that was not present for the original memory. Not only do individuals with this condition experience less vivid and decontextualized episodic memory for all events outside of the traumatic experience, but also, individuals with PTSD have difficulties with identifying the source of both emotional and neutralFichtenholtz, H., Qin, J. J., Mitchell, K. J., Johnson, D. C., Southwick, S. M., Johnson, M. K., et al. (2008, May). PTSD patients' memory for neutral pictures in blocked and intermixed lists. Paper presented at the annual meeting of the Association for Psychological Science, Chicago. information overall. Those with PTSD may have poorer recall for the source of their knowledge due to deficits in the encoding process which creates weaker relationships between the item and its context.
Depression Depression is associated with overly generalized memories and individuals with depression perform more poorly on source memory attribution tasks as compared to non-depressed individuals. These individuals show a memory bias for remembering negative information, possibly due to enhanced amygdala activity during the encoding of emotional (particularly negative) information. Overall, there is a relationship between the emotional arousal of an episode and its source memory – there is some evidence that the enhanced processing of negative memories results in poorer source memory, and thus individuals who are depressed would have increased amounts of source amnesia.
Hypnosis Hypnosis as a cause of source amnesia involves carrying out hypnosis and having the subjects remember post-hypnotically, experiences they had during hypnosis as tested by asking the individuals about esoteric knowledge that they learned during hypnosis. These individuals typically have no recall of the hypnotic experience whatsoever; however, when tested on these obscure pieces of knowledge they are able to supply the correct answer, demonstrating their source amnesia. The subjects often attribute their knowledge of the obscure facts to learning experiences other than during hypnosis (e.g.: "I read it somewhere," "Somebody must have told me," etc.).
Diagnostic tests
Wisconsin Card Sorting Test (WCST) The Wisconsin Card Sorting Test is widely used in clinical settings to test for cognitive impairments, such as frontal lobe disorder which has been associated with source amnesia.
Procedure Two sets of 12 identical cards forms the visuo-spatial component for the test. The figures on the cards differ with respect to color, quantity, and shape. The participants are then given a pile of additional cards and are asked to match each one to one of the previous cards.
Results Patients with frontal lobe dysfunction and ultimately source amnesia, will have much greater difficulty finishing this task successfully through method of strategy.
Verbal fluency test The verbal fluency test is a widely and commonly used test to assess for frontal lobe dysfunction in patients.
Procedure Participants are asked to generate words beginning with letters that had previously been introduced to them (e.g.: generate a word beginning with 'A' or 'R'). They are given three 1-min trials (one trial per letter). The goal is to say as many different words possible that begin with the given letter.
Results The Verbal fluency test can assess for damage in the prefrontal lobes, which has been associated with patients who have source amnesia. Patients with frontal lobe disorder have trouble putting verbal items into a proper sequential order, monitor personal behaviors as well as a deficient judgment in recency. All of these behaviors are required for the proper recall of the source of a memory.
Stroop Color-Naming Task
Research has shown that the Stroop effect has numerous findings related to age and its effect on memory. The test measures speed and accuracy skills of naming colors and colored words, to determine the effects of aging on the brain which is thought to be a cause of source amnesia.
Procedure The participant is asked to read a series of related word-reading and color-naming trials. In the first component of the task, known as the word-reading condition of the task, the participant is asked to read as quickly as possible a series of color names printed either in white or other various colors. The participant is then asked to name the color of a series of colored blocks.