Inhibitory processes in the misinformation effect : negative consequences of an adaptive process
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Recent research has suggested the seemingly ironic possibility that in order to be able to remember effectively, we must be able to forget. Despite the fact that forgetting is typically conceived of as a wholly negative experience it may, nonetheless, have adaptive consequences for the efficient updating of memory. Without a method for setting aside out-of-date or unwanted information, we may be unable to satisfy current memorial goals. Recent research suggests that inhibitory processes operating during retrieval may be responsible for the temporary forgetting of unwanted information so that desired memories can be successfully retrieved (referred to as retrieval-induced forgetting, M.C. Anderson, Bjork & Bjork, 1994). The present thesis attempts to enhance our understanding of the basic mechanisms that underlie our ability to update our memories by examining the role of inhibitory processes in the misinformation effect. The misinformation effect is a form of memory error whereby individuals mistakenly report post-event misleading information rather than information that was originally encoded during an initial study phase (e.g., E.F. Loftus, 1979a). In order to examine whether the underlying mechanisms in the misinformation effect (and more generally in memory updating) are inhibitory in nature, five theory-driven experiments were conducted and reported in this thesis. An inhibitory account of misinformation effects assumes that significant misinformation effects should only be detected when information from an initial event has been inhibited, and therefore is unavailable to conscious inspection. A new paradigm was designed for investigating the memorial processes responsible for the misinformation effect, which combined key features from the retrieval practice paradigm with that of the misinformation paradigm (cf. E.F. Loftus, Miller & Burns, 1978). In Experiments 1 and 2, the boundary conditions of varying the retrieval status of target items within this new paradigm were explored. More specifically, in Experiment 1, significant misinformation effects were found only when misleading information was presented on items that were subject to retrieval-induced forgetting, i.e., the original information was unavailable to conscious inspection, leaving only the post-event information available for retrieval. A further test of the retrieval-induced forgetting account was examined in Experiment 2 whereby the presence of retrieval induced forgetting was manipulated through the insertion of a delay. Experiment 2 indicated that the production of misinformation effects was dependent on retrieval-induced forgetting remaining active (i.e., under condition of no delay, or where a delay occurred between study and retrieval practice). In contrast, significant misinformation effects were not found when retrieval-induced forgetting dissipated over a retention interval (i.e., when a delay was inserted between retrieval practice and final test). Despite Experiments 1 - 2 suggesting that retrieval-induced forgetting may play an influential role in the production of misinformation effect, the new misinformation paradigm cannot differentiate between the possible inhibitory and non-inhibitory processes that may underlie retrieval-induced forgetting. This is primarily due to the new paradigm employing a free recall test rather than using a memory test that can separate the actions of inhibitory from non-inhibitory processes. However, as the ‘independent probe’ method (M.C. Anderson & Spellman, 1995) can perform this task, it was modified for use in Experiments 3 - 5 , which more closely examined whether inhibitory processes were indeed responsible for both retrieval-induced forgetting and misinformation effects. More specifically. Experiment 3 found that inhibitory processes were the primary mechanism behind retrieval-induced forgetting, while Experiment 4 demonstrated that any item that competes with target material for retrieval is subject to inhibition (referred to as cross-category and second-order inhibition). Experiment 5 extended the findings of Experiment 3 and 4, and found that inhibitory processes were not only responsible for misinformation effects, but that all inhibited information is susceptible to the effects of post-event information. The present studies suggest that that an adaptive function on inhibition (i.e., the updating of memory) may be responsible for unwanted and undesired effect in memory under certain circumstances (i.e., the production of misinformation effects and eyewitness errors). In order to examine more fully the role of inhibitory processes in the production of misinformation effects, and more generally, in memory updating, the present thesis considers both classical and modern research on forgetting. Chapter 1 outlines recent theorising that forgetting should not be considered an exclusively negative phenomenon, and that it should, in fact, be considered an essential and necessary process that keeps our memory systems running optimally. This possibility is examined in more thorough detail in Chapters 2 and 3. Chapter 2 considers both classical interference research, and the more recent inhibitory accounts of intentional forgetting, while Chapter 3 examines how successful these inhibitory accounts have been applied to research concerning unintentional forgetting. In contrast. Chapter 4 examines a rather different approach to memory updating as viewed through misinformation studies. A new paradigm for investigating misinformation effects is introduced in Chapter 5, and the empirical Chapters 5 - 9 discuss the application of this new paradigm to the investigation of misinformation effects. Finally, the conclusions and implications of unintentional forgetting for theories of memory updating are discussed in Chapter 10. The work presented in this thesis suggests that not only can inhibition promote the updating of memory, but it can also leave our memories vulnerable to the unintentional integration of incorrect information.
Thesis, PhD Doctor of Philosophy
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