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Emerging Cognitive Neuroscience and Related Technologies Appendix F True and False Memories as an Illustrative Case of the Difficulty of Developing Accurate and Practical Neurophysiological Indexes of Psychological States An important issue for cognitive neuroscientists concerns efforts to determine whether a person is reporting a true experience or one that is false but believed. In the last decade, there have been innumerable research efforts designed to distinguish true from false memories. Earlier work examining behavioral differences between true and false memories revealed that group differences were sometimes found (for example, more sensory details in true-memory reports) (Schooler et al., 1986). However, the statistical group differences did not enable reliable classification of any particular memory report as to its authenticity. Some work with neuroimaging has attempted to locate differences in the brain that might reveal something about true and false memories. The goal of much of the work has been to demonstrate that true and false memories have different neural signatures (Curran et al., 2001; Fabiani et al., 2000; Miller et al., 2001). The allure of such research has been so great that considerable effort is likely to be devoted in the future to the neurophysiology of false memory. Despite some progress, we are far from being able to use neuroimaging techniques to tell us about the veracity of particular memories, because the reported findings are based on group averages. A group of true memories might show more activity in the visual cortex, whereas a group of false memories might show more activity in the auditory cortex. Group averages do not allow us to focus on an individual memory and to discern reliably whether it is true or false. Another potential problem with neuroimaging work on false memory is that such studies typically involve memory for words recently learned, and the few studies that have used this procedure have yielded inconsistent results. The methodological constraints of neuroimaging tools such as functional magnetic resonance imaging (fMRI) and event-related potentials make it difficult to study rich false memories.
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Emerging Cognitive Neuroscience and Related Technologies A notable exception can be found in the work of Okado and Stark (2005), who examined true and false memories in the context of a misinformation experiment and thus studied richer false memories. Misinformation studies show how readily memory can become skewed when people are fed misinformation (Loftus, 2005). A typical misinformation study uses a simple three-stage procedure: subjects see a complex event, such as a simulated automobile accident; half the subjects receive misleading information about the accident, and the other half get no misinformation; and finally, all subjects try to remember the original accident. In one study that used that procedure, subjects saw an accident, and some of them later received misinformation about the traffic sign at the intersection in question. The misled subjects got the false suggestion that the stop sign that they had actually seen was a yield sign. When asked later what kind of traffic sign they remembered seeing, those who had been given the false suggestion tended to adopt it as their memory and claimed to have seen a yield sign. Hundreds of similar studies show that misinformation can change a person’s recollection in predictable ways. In an fMRI study that compared true memories with false memories created by misinformation, some group differences emerged (Okado et al., 2006). For example, the true-memory reports were associated with greater activation in the visual cortex, whereas the false-memory reports were associated with greater activation in the auditory cortex. However, the overwhelming impression from the research is that true and false memories are activating similar portions of the brain and that a particular memory cannot be reliably classified as true or false. Richard McNally and his collaborators (McNally, 2003) studied people who had very rich, although likely false, memories of alien abduction have been studied. One study explored whether people who believe they have been abducted exhibit heightened physiological reactivity (heart rate and skin conductance) that occurs commonly in patients who have posttraumatic stress disorder (PTSD) when they think about their traumas. The “abductees” studied had experienced apparent sleep paralysis and hypnopompic hallucinations, which are vivid dreamlike hallucinations that occur as one is waking up, such as seeing figures hovering near their beds. Most had recovered memories with such techniques as guided imagery and hypnosis. Some of the recovered memories involved sexual intercourse with aliens or having sperm extracted for breeding purposes. Their physiological reactions were similar to those seen in PTSD patients who listen to audiotaped scripts of their traumas. Thus, expressed emotion is no guarantee that a memory is true. There is a further concern in the true-memory–false-memory distinction: In many of the real-world cases, there have been attempts to get people to remember, to discuss their memories, to imagine details, and so on. Those very attempts can increase the detail and vividness of false memories—the very characteristics that lead (or rather mislead) people to believe that the memories are real.
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Emerging Cognitive Neuroscience and Related Technologies REFERENCES Curran, Tim, Daniel L. Schacter, Marcia K. Johnson, and Ruth Spinks. 2001. Brain potentials reflect behavioral differences in true and false recognition. Journal of Cognitive Neuroscience 13(2):201-216. Fabiani, Monica, Michael A. Stadler, and Peter M. Wessels. 2000. True but not false memories produce a sensory signature in human lateralized brain potentials. Journal of Cognitive Neuroscience 12(6):941-949. Loftus, Elizabeth F. 2005. Planting misinformation in the human mind: A 30-year investigation of the malleability of memory. Learning and Memory 12(4):361-366. McNally, Richard J. 2003. Remembering Trauma. Cambridge, MA: Harvard University Press. Miller, Antoinette R., Christopher Baratta, Christine Wynveen, and J. Peter Rosenfeld. 2001. P300 latency, but not amplitude or topography, distinguishes between true and false recognition. Journal of Experimental Psychology: Learning, Memory, and Cognition 27(2):354-361. Okado, Yoko, Elizabeth Loftus, and Craig E.L. Stark. 2006. Imaging the reconstruction of true and false memories through sensory reactivation. Paper read at 13th Annual Cognitive Neuroscience Society Meeting, April 8-11, 2006, San Francisco, CA. Okado, Yoko, and Craig E.L. Stark. 2005. Neural activity during encoding predicts false memories created by misinformation. Learning and Memory 12(1):3-11. Schooler, Jonathan W., Delia Gerhard, and Elizabeth Loftus. 1986. Qualities of the unreal. Journal of Experimental Psychology: Learning, Memory, and Cognition 12(2):171-181.