Introduction
One of the most unexpected aspects of our memory is the existence of false memories. According to Roediger and McDermott (1995), this phenomenon concerns two kinds of memory errors : remembering events that never happened (memories creation) or remembering them quite differently from the way they happened (memories distortion). This study was proposed to examine one type of memories creation : intrusions. Indeed, we were interested in this effect because it appears when people produce a non studied item in free recall tests.
The Deese-Roediger-McDermott Pardigm
Among the many experimental techniques developed to study these memory distortions, the Deese Roediger McDermott (DRM) paradigm is one of the most used. The DRM involves presenting to participants some lists of 15 semantically related words that converge on a single, non-presented item, known as the critical lure (Roediger & McDermott, 1995). At the end of the presentation of each list, the participant must perform an immediate free recall. Authors’ results have shown that participants incorrectly recalled critical lures at high rates (approximately 50%). Thus, many authors have attempted to understand the processes that underlie the production of intrusions in this paradigm.
How Can False Memories Occur ?
Many hypotheses have been suggested in literature to account for the production of intrusions in the DRM task. The theory of Activation-Monitoring postulates that false memories are produced by the conjunction of two processes (Roediger, Watson, McDermott, & Gallo, 2001). First of all, during the presentation of the list, activation automatically spreads from those words to the critical lure in semantic memory (Meade, Watson, Balota, & Roediger, 2007). However, this process alone is not enough to explain why the participant recall critical lures. Indeed, during the free recall task, the participant must discriminate the source of the words that he remembered, but the activation of the critical lure makes the intervention of the monitoring process difficult.
To summarize, when a participant does not produce the critical lure, two reasons can be mentioned : either the threshold activation of the critical lure in memory has not been reached, or the source monitoring worked well.
Who is Especially Affected by False Memories ?
Several studies using the DRM paradigm showed that older adults are more prone to memory distortions than younger adults. (Schacter, Koutstaal, & Norman, 1997). This result could be explained by a source-monitoring issue. Additionally, studies carried out have shown that Alzheimer’s patients produce less critical lures than older adults (Balota et al., 1999 ; Budson, Daffner, Desikan, & Schacter, 2000). So, the purpose of this study was to examine why Alzheimer’s patients are less vulnerable to false memories than older adults in a DRM task. More precisely, the track of a critical lure activation failure has been investigated (because the source monitoring process is known to be severely impaired in Alzheimer’s disease).
To test this hypothesis, Alzheimer’s patients performed a lexical decision task that did not require the intervention of source monitoring process (Meade, Watson, Balota, & Roediger, 2007). Consequently, this kind of task allowed us to obtain a relatively pure measure of the activation of critical lures, through a semantic priming effect. Participants were asked to decide as quickly as possible strings of letters as words or nonwords. The material used included words from DRM lists, critical lures, neutral words and nonwords. We had expected that participants showed no decision time difference between kinds of words.
Results and Discussion
Statistical analysis showed shorter lexical decision latencies for critical lures than for other kinds of words. So, these findings suggest that the activation process of critical lures is preserved at the task’s start in Alzheimer’s patients, as in older adults. To try to explain this phenomenon, a major hypothesis has been postulated : the mnemonic trace of critical lure would be too quickly forgotten (because of episodic memory disorders) to be recalled later. So, future research should explore if the critical lure is still activated at the end of the presentation of the DRM list.
Bibliography
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Roediger, H. L., Watson, J. M., McDermott, K. B., & Gallo, D. A. (2001). Factors that determine false recall: A multiple regression analysis. Psychonomic Bulletin & Review, 8(3), 385-407.
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