The impact of stress and warning on the creation of false memories

The purpose of this study was to analyse the impact of stress and warning on creation of false memories and correctly recalled words. Participants were 60 in total, 11 males and 49 females. Participants were randomly divided into four groups; group that received stress and warning, group that received stress, group that received warning and group that received neither stress nor warning. The results showed that the non-presented critical words were recalled in 22% of cases and studied words were correctly recalled in 54% of cases. The results also showed that warning and stress did not have a significant impact on the creation of false memories, although there was a trend towards greater impact of warning on those participants who received stress compared to those participants who did not receive stress. Warning did have a significant impact on studied words where those participants who received warning recalled fewer studied words compared to those who didn’t receive warning. Lack of significant impact of warning and stress on false memory might be due to too few participants in each group. STRESS AND WARNING IN FALSE MEMORIES 3 Foreword and Acknowledgement Submitted in partial fulfillment of the requirements of the BSc Psychology degree, Reykjavík University, this thesis is presented in the style of an article for submission to a peer-reviewed journal. I would like to thank my supervisor Kamilla Rún Jóhannsdóttir Ph.D, for her guidance, great support and good advise throughout this project. I would also like to thank all my participants, but their participation made my project possible. As well I want to thank Ásgeir Erlendsson for pre-recording all the word lists that were used in the research. Finally I want to thank my family for supporting me while working on this project and during my studies in the psychology program at Reykjavík University. Without all this support it would have been hard for me to finalize this project. STRESS AND WARNING IN FALSE MEMORIES 4 The concept of false memories refers to when people remember events that never happened or that they remember them quite differently from the way they actually happened (Roediger & McDermott, 1995). In recent years there has been an increased interest in when and why people form false memories (e.g. Roediger & McDermott, 1995 & Loftus, 1992). Deese was the first to introduce thematic word lists in 1995 in order to analyse false memories (see Roediger & McDermott, 1995). His method involved using thematic word lists where all the words are similar to one critical word. For example, for the critical word sleep, the list words were bed, rest, awake, tired, dream, wake, snooze, blanket, doze, slumber, snore, nap, peace, yawn and drowsy (Roediger & McDermott, 1995). Deese developed 36 word lists, each list contained 12 words and were related to one critical word. All the words on the lists were read out loud for the participants except for the critical word (which will from now on be referred to as the non-presented critical word). Deese believed that the thematic word lists would lead to the participants thinking that they had heard the non-presented critical word read out loud. When each word list had been read out loud the participants were supposed to use free recall to write down the words they thought they had heard. The non-presented critical word, which quite frequently was written down by the participants, is classified as false memory (as discussed in Roediger & McDermott, 1995). Roediger and McDermott (1995) based their study on Deese’s thematic lists. Roediger and McDermott created 24 thematic word lists, which contained 15 words each. The words in the lists were all strongly related to one non-presented critical word. In their experiment they used six word lists from Deese (1959), which had shown the highest frequency of false recall. Roediger and McDermott used both free recall and recognition test to see if participants recalled the non-presented critical word. The results showed that the non-presented critical word was falsely recognized in 40% of cases and was recognized more frequently than nonstudied words presented on the recognition test. Their findings confirmed the results from STRESS AND WARNING IN FALSE MEMORIES 5 Deese’s studies of high levels of false memories in a single-trial free recall task. In addition, Roediger and McDermott found that the non-presented critical word was recalled at almost the same level as items that were presented in the middle of the list. The non-presented critical word was also recalled more often than other similar words that were not presented in the list. Furthermore, more than half of the participants were sure that the non-presented critical word had appeared in the list. Gallo, Roberts and Seamon (1997) performed a research to see if something could prevent individuals from creating false memories. They divided the participants into three groups. The first group was not told about the false recognition effect, but they were given standard instructions instead and instructed to try to remember as many words as possible for the recognition test. In the second group the participants were informed to be careful on the recognition test to reduce their false recognition. The third group was forewarned about the false recognition with detailed information and examples. The participants in the third group were specifically told that the study lists were designed to try to make them falsely recognize related but non-presented critical words. This condition allowed participants the chance to devise strategies to reduce or eliminate the false recognition effect. Results from the study revealed that when participants were uninformed about the false memories, they established a strong false recognition effect. The results from the second group indicated that when participants were asked to be careful on the recognition test it reduced the hit rates for the studied words as well as reducing the participant ́s recognition regarding the non-presented critical words. However, asking participants to be cautious did not prevent them from creating false memories. Watson, Bunting, Poole and Conway (2005) examined whether individuals’ working memory span would affect the extent to which a warning could be used to reduce the false memory effect. Their results revealed that those participants with a high working memory STRESS AND WARNING IN FALSE MEMORIES 6 span created less false memories but only if they received a warning. That is individuals with a low working memory span are unlikely to reduce the creation of false memories even if they are warned about the false memory effect. Participants with a high working memory span also recalled more studied words than the participants with a low working memory span regardless of whether they received a warning or not. The existing literature on false memories suggests that the false memory effect is a robust effect not controlled by working memory capacity and not easily avoided even when participants are warned about the effect. But more studies are needed to further examine false memories and when and how they are created. For example, one topic of interest would be to analyse the impact of stress on false memories. This would both have applied relevance (e.g. stressful questioning of a witness) but also theoretical as studies suggest both that stress to a point can increase cognitive performance (Milkman & Sunderwirth, 2010) and also a high level of stress can impair cognitive performance (Lupien & McEwen, 1997; Vedhara, Hyde, Gilchrist, Tytherleigh & Plummer, 2000). For example, research has shown that acute highlevels of cortisol in humans, which is a stress hormone, affects both memory and cognition (Lupien & McEwen, 1997). Research by Vedhara et.al., (2000) showed that stress has been found to influence each memory phase in a different way, where performance on short-term memory increased and performance on selective attention and divided attention deteriorated when participants were stressed. However, in this research the stress did not seem to have an impact on working memory. Oei, Everaerd, Elzinga, Van Well and Bermond (2006) found that stress does decrease performance on a difficult working memory task but does not have an impact on an easy working memory task. The impact of stress on working memory may therefore depend on the difficulty level of the task, or possibly on the method used to stress the participants. STRESS AND WARNING IN FALSE MEMORIES 7 Stress, or high levels of glucocorticoids, also seems to affect participants’ performance on the false memory test (Payne, Nadel, Allen, Thomas & Jacobs, 2002). Even moderate stress levels can impair memory function (de Quervain, Roozendaal, Nitsch, McGaugh & Hock, 2000). Payne et.al., (2002) examined whether induced stress would have an impact on the creation of false memories. The participants’ stress was induced by using the Trier Social Stress Test (Kirschbaum, Pirke & Hellhammer, 1993), which involved participants needing to prepare a speech for ten minutes and then deliver that same speech in five minutes in front of a one-way mirror where three trained investigators were on the other side to evaluate. The Deese-Roediger-McDermott word lists were used in order to try to elicit false memories. The results revealed that stress did not have an impact on the accuracy of the memory for studied words. However, stress did increase the false recognition rate were the stressed participants falsely recognized the non-presented critical words in 77% of cases compared to 61% for the non-stressed participants. This is a very high rate of false memories and much higher than Roediger and McDermott (1995) were getting in their research. The varied impact of stress on different cognitive components could be explained partially by different types of methods used in order to induce participants’ stress. The Trier Social