Processes behind false memories in the Deese-Roediger-McDermott paradigm

It is a part of the common belief in many cultures, as the European culture, that human beings make mistakes and errors when they think and reason. However, when people talk about cognitive illusions barely they are thinking to memory functions (for an extensive review see: Pohl, 2010). The reason is that the better-known domain of the cognitive illusions are the optical illusions. The main characteristic of whatever kind of illusion is the involuntariness, i.e. they occur without a deliberate will and are hard to avoid. However, they are all different for the cognitive function involved (perception, memory, thinking, judgment and decision-making). Let us consider some famous perceptual illusions discovered by the pioneer authors of the Gestalt psychology. In Figure 1 are reported three famous visual illusions. The first is the Ponzo’s illusion (1911), which consists in seeing the lower horizontal line as shorter than the higher line. Actually, the two line are equal. The second illusion consists in perceiving a brightness changing in the horizontal bar due to the background gradient (Kanizsa, 1955). Actually, the horizontal bar is monochromatic. The third illusion consists in perceiving a triangle with a more intense white than the background white (Tanca, Grossberg, & Pinna, 2010). In the case of the optical illusions, the discrepancy between reality and illusion created is immediately evident and costs low effort, because the subjective perception can be immediately compared with the external stimulus. The reader can control the illusions measuring the length of the two bars in the Ponzo’s illusion, isolating the central grey bar from the background in the simultaneous contrast illusion, and simply shifting the attention focus from the Kanizsa’s triangle to one side of it. This is not always possible when we refers to memory, judgments and decision-making. In the former case, we could check whether we remembered something right just when the external source is still available or captured in some modern storage technology (a book, a movie, a picture, a data-file, etc.). When this is not possible, the memory illusion could be considered a specific case of judgment illusion. When we have a doubt on what we have recollected from our memory, we decide to trust or not of our memory basing that decision on our confidence (i.e., memory judgment). When we talk about pure judgment and illusion in decision domain, instead, we need a normative theory that tells us how to decide rationally, in order to define where we make a mistake (Gigerenzer, 1996; Rumiati & Bonini, 2001). Nevertheless, it is crucial to do not confuse the cognitive illusion from simple errors, misunderstandings or ordinary forms of forgetting. Generally, to distinguish cognitive illusions from simple distortions we need to observe robustness in replicating that illusion (Roediger, 1996). This is way cognitive illusions attract our attention and makes meaningful for the researcher to explain the unexpected finding as a cognitive illusion. The main aim of this dissertation is to describe the psychological processes involved in the production of false memories as measured by the Deese-Roediger-McDermott (DRM) paradigm (Roediger & McDermott, 1995). It is a particular case of the associative memory illusion (Roediger, 1996) consisting in remembering words not presented in a previous study phase. This paradigm has been widely used in the laboratory settings to study the memory process that cause false memories (for a review see: Gallo, 2010). The present dissertation consist in three main sections. An introductory section in which I reported the theoretical background and the questions that I tried to answer during my PhD. In the first section, I included also a paragraph on methodology used and in which I explain the methodological background of few statistical tools that I adopted. In the middle section, I reported all the experiments with the respective sub-section relative to introduction, method, results and discussion. I reported the conclusions and the theoretical implications of the present work in the last part of this dissertation.