Sleep Deprivation and False Memories PDF (Psychological Science)

Psychological Science http://pss.sagepub.com/ Sleep Deprivation and False Memories Steven J. Frenda, Lawrence Patihis, Elizabeth F. Loftus, Holly C. Lewis and Kimberly M. Fenn Psychological Science published online 16 July 2014...

Psychological Science http://pss.sagepub.com/ Sleep Deprivation and False Memories Steven J. Frenda, Lawrence Patihis, Elizabeth F. Loftus, Holly C. Lewis and Kimberly M. Fenn Psychological Science published online 16 July 2014 DOI: 10.1177/0956797614534694 The online version of this article can be found at: http://pss.sagepub.com/content/early/2014/07/15/0956797614534694 Published by: http://www.sagepublications.com On behalf of: Association for Psychological Science Additional services and information for Psychological Science can be found at: Email Alerts: http://pss.sagepub.com/cgi/alerts Subscriptions: http://pss.sagepub.com/subscriptions Reprints: http://www.sagepub.com/journalsReprints.nav Permissions: http://www.sagepub.com/journalsPermissions.nav >> OnlineFirst Version of Record - Jul 16, 2014 What is This? Downloaded from pss.sagepub.com at Universiti Teknologi MARA (UiTM) on July 18, 2014 534694 research-article2014 PSSXXX10.1177/0956797614534694Frenda et al.Sleep Deprivation and False Memories Psychological Science OnlineFirst, published on July 16, 2014 as doi:10.1177/0956797614534694 Research Article Psychological Science Sleep Deprivation and False Memories 1 ­–8 © The Author(s) 2014 Reprints and permissions: sagepub.com/journalsPermissions.nav DOI: 10.1177/0956797614534694 pss.sagepub.com Steven J. Frenda1, Lawrence Patihis1, Elizabeth F. Loftus1, Holly C. Lewis2, and Kimberly M. Fenn2 1 Department of Psychology and Social Behavior, University of California, Irvine, and 2 Department of Psychology, Michigan State University Abstract Many studies have investigated factors that affect susceptibility to false memories. However, few have investigated the role of sleep deprivation in the formation of false memories, despite overwhelming evidence that sleep deprivation impairs cognitive function. We examined the relationship between self-reported sleep duration and false memories and the effect of 24 hr of total sleep deprivation on susceptibility to false memories. We found that under certain conditions, sleep deprivation can increase the risk of developing false memories. Specifically, sleep deprivation increased false memories in a misinformation task when participants were sleep deprived during event encoding, but did not have a significant effect when the deprivation occurred after event encoding. These experiments are the first to investigate the effect of sleep deprivation on susceptibility to false memories, which can have dire consequences. Keywords false memory, sleep deprivation, sleep, misinformation, suggestibility Received 8/18/13; Revision accepted 3/23/14 Memories are not “recorded” in the brain. Rather, they are memories can arise in a number of ways. One common reconstructed using information from multiple sources, method for studying false memories in the laboratory is and they can change following exposure to misleading the misinformation procedure: Participants encode some postevent information or other suggestive influences (for stimuli (usually videos or photographs), later see mislead- reviews, see Frenda, Nichols, & Loftus, 2011; Lindsay, ing information about the material that they encoded, and 2008). Moreover, people sometimes recall entire events finally, take a memory test (e.g., Zhu et al., 2010). and experiences that never happened, and these false Participants frequently incorporate the misleading infor- memories can be vivid, emotional, and held with great mation into their memories for the original materials. One confidence (e.g., McNally et al., 2004; see also Loftus & strength of this approach is that the procedure includes Ketcham, 1994). Memory errors can have serious conse- three discrete stages (encoding, misinformation, retrieval quences: For example, eyewitness misidentifications are at test) that theoretically correspond to stages of a process thought to be the leading cause of wrongful criminal that unfolds in real-world contexts (e.g., a person wit- convictions in the United States (e.g., Garrett, 2011). nesses a crime, is later exposed to misleading information, Many studies have investigated situations that lead to the and repeats his or her memory as testimony). formation of false memories, but one unexplored ques- Related studies have shown that people sometimes tion is whether sleep deprivation affects memory sug- recall witnessing events that they never saw. Specifically, gestibility. Accordingly, we investigated the effect of sleep people sometimes falsely report that they viewed video deprivation on susceptibility to false memories. footage of high-profile news events, even when no such False Memories Corresponding Author: Steven J. Frenda, Department of Psychology and Social Behavior, Early studies showed that suggestive questioning can School of Social Ecology, 4201 Social & Behavioral Sciences Gateway, influence memory reports (e.g., Loftus & Palmer, 1974), Irvine, CA 92697-7085 and since then, myriad studies have shown that false E-mail: [email protected] Downloaded from pss.sagepub.com at Universiti Teknologi MARA (UiTM) on July 18, 2014 2 Frenda et al. footage exists (e.g., Princess Diana’s fatal car collision— this topic has been conducted using DRM procedures. Ost, Vrij, Costall, & Bull, 2002; see also Crombag, Virtually no research has investigated whether sleep Wagenaar, & van Koppen, 1996; Ost, Granhag, Udell, & deprivation increases susceptibility to false memories for Hjelmsäter, 2008). Often, these participants provide richer, real-world stimuli.1 In the experiments reported detailed memory reports. These findings are in line with here, we capitalized on the multiple methods for creat- research demonstrating that imagined events are some- ing false memories in the laboratory. In Experiment 1, times confused as being actual memories (e.g., Garry, we tested whether self-reported sleep duration on the Manning, Loftus, & Sherman, 1996; Hyman, Husband, & night prior to an experiment was associated with false Billings, 1995). A strength of this approach is the use of memories of witnessing a news event and with false actual news events—rich with emotion and real-world memories in a misinformation task. In Experiment 2, we significance—as the stimuli. manipulated sleep deprivation to examine its effects on Finally, a common method for creating false memories the formation of false memories at various stages of a in the laboratory is the Deese-Roediger-McDermott misinformation task. (DRM) paradigm (Deese, 1959; Roediger & McDermott, 1995). In the DRM task, participants learn lists of words (e.g., bed, rest, awake, tired) that are semantically associ- Experiment 1 ated with a nonpresented word—the critical lure (sleep). Method On subsequent memory tests, participants often recall seeing the nonpresented critical lures. False memories in Participants. We drew the data set for Experiment 1 the DRM task have been described as associative, or gist- from a large, multisession study. One hundred ninety- based, errors (see Schacter, Guerin, & St. Jacques, 2011). three undergraduates (mean age = 20.3 years, SD = 3.5; Although the DRM paradigm is widely used in false 76% female, 24% male) at the University of California, memory research, its relevance to false memories of Irvine, completed a battery of personality measures and events in more naturalistic contexts has been controver- cognitive tasks for course credit. Only procedures rele- sial (e.g., Pezdek & Lam, 2007; Wade et al., 2007). vant to the current study are described here. News event. Participants completed a questionnaire that Sleep Deprivation included a passage describing the plane crash in Shanks- Sleep deprivation appears to be increasingly prevalent ville, Pennsylvania, on September 11, 2001, and claiming (Schoenborn & Adams 2010), and it impairs performance that video footage of the crash had been widely seen on across a wide range of cognitive tasks. It slows reaction the news and the Internet (although images of the after- time (Koslowsky & Babkoff, 1992), decreases working math were widely available, the crash was not captured memory capacity (Chee & Choo, 2004), interferes with on video). The critical item on the questionnaire asked normal learning (Drummond & Brown, 2001), and impairs participants whether they had seen “video footage of the executive function (Nilsson et al., 2005; for reviews, see plane crashing, taken by one of the witnesses on the Harrison & Horne, 2000, and Thomas et al., 2000). Thus, ground.” Participants responded by selecting “yes” or “no.” sleep deprivation might also increase false memory. Prior to debriefing, research staff conducted short, However, studies investigating sleep deprivation and false audio-recorded interviews to probe participants’ memory memory have shown mixed results. In two experiments, for the footage. Critically, interviewers repeated the sug- participants studied DRM lists before a night of either gestion that a video of the crash had been widely seen sleep or sleep deprivation; testing took place the follow- and asked participants to indicate verbally whether or ing day. One study showed higher rates of false recogni- not they had seen the footage (for details on coding, see tion in sleep-deprived participants, compared with rested the Supplemental Material available online). participants (Diekelmann, Landolt, Lahl, Born, & Wagner, 2008), but the subsequent study found no differences in Misinformation task false recall between the groups (Diekelmann, Born, & Event encoding. We assembled two sets of photo- Wagner, 2010). Finally, in another study, participants graphs from materials developed by Okado and Stark learned DRM lists at night and then either slept or were (2005). One set depicted a man breaking into a parked sleep deprived. After a period of recovery sleep, they car, and the other depicted a woman encountering a thief were tested, and no differences in false recall emerged who steals her wallet. Each set contained 50 photographs between the groups (Darsaud et al., 2010). that were presented in a fixed order for 3,500 ms each. Thus, the evidence suggesting that sleep deprivation Participants were told that they would be shown a series contributes to the formation of false memories is sparse of images and that they would later be asked questions and inconsistent. Furthermore, most of the research on about them. Downloaded from pss.sagepub.com at Universiti Teknologi MARA (UiTM) on July 18, 2014 Sleep Deprivation and False Memories 3 a After he takes her wallet out a. I saw it in the pictures only of her purse, where does he b. I saw it in the narratives only “... he took her wallet and hide it? c. I saw it in both and they put it away in his pants a. In his jacket pocket were the same pocket.” d. I saw it in both and they b. In his pants pocket were different c. In his sleeve e. I guessed Photos Misinformation Memory Test Source Test b Morning-Encoding Condition Sleep or Deprivation Photos Misinformation Test Evening 8 Hours Morning (22:30) (9:00) Evening-Encoding Condition Photos Sleep or Deprivation Misinformation Test Evening 8 Hours Morning (22:30) (9:00) Fig. 1. Experimental procedure and design. The misinformation procedure in Experiments 1 and 2 is illustrated in (a). After viewing two sets of photographs depicting events, participants read narratives that included misinformation about the events. Later, participants took a three- alternative forced-choice test of their memory for the photographs and a source test on which they indicated where they had acquired the information they used to answer each question. In Experiment 2 (b), participants arrived at the lab in the evening to perform the misinforma- tion procedure. Some participants completed the encoding phase (viewing photos) of the procedure in the evening, and others completed it the following morning. Within each encoding condition, some participants remained awake overnight, and others were allowed to sleep for 8 hr. Misinformation narrative. Approximately 40 min after select an answer on the basis of their memory for the participants viewed the photographs, they read two text photographs. Critical questions pertained to information narratives—one for each photo set—that told the stories that was presented inaccurately in a narrative; one of of the photographs. Each narrative contained three state- the response choices was correct (i.e., consistent with ments that directly contradicted the events shown in the an original photograph), one was consistent with the photographs. Therefore, each participant read a total misinformation (i.e., consistent with an inaccuracy in the of six pieces of misinformation—three for each photo narrative), and one was a novel foil (i.e., a possibility set—embedded among true information. We created two not shown in the photographs or mentioned in the nar- versions of the study’s misinformation phase; for both rative). After participants completed the multiple-choice narratives, each participant received misinformation cor- test, they completed a source test in which they viewed responding to one of two possible sets of questions on each question again and elaborated on their answer the memory test. Participants were instructed to focus choice by indicating where they had acquired the infor- on the narratives but were not warned that they might mation: “in the pictures only,” “in the narratives only,” “in encounter inconsistencies. both and they were the same,” “in both and they were different,” or “I guessed.” The source test allowed us to Test. Approximately 20 min after participants read the assess whether or not the participants remembered see- narratives, they took a three-alternative forced-choice ing misinformation in the original images. test of their memory for the photographs. Each ques- tion pertained to a specific detail depicted in one of the Procedure. In a preliminary session at the lab, partici- photographs (Fig. 1a), and participants were asked to pants consented to participation, provided demographic Downloaded from pss.sagepub.com at Universiti Teknologi MARA (UiTM) on July 18, 2014 4 Frenda et al. 5 Hr or Fewer on any demographic variables (e.g., age, gender, More Than 5 Hr race-ethnicity). 50% News event. We first compared the two groups’ responses 40% to the news-event questionnaire item. Participants in the restricted-sleep group were significantly more likely than Response Rate participants in the reference group to report that they had 30% seen the video (54% vs. 33%), χ2(1, N = 193) = 4.2, p =.04, ϕc =.15. However, the groups did not differ when ques- 20% tioned in the follow-up interview: 21% of the restricted- sleep group and 20% of the reference group persisted in 10% their claim that they had seen the video, χ2(1, N = 193) = 0.03, p =.86. Thus, restricted sleep was associated with initial false reports on the questionnaire, but not with 0% MCR False Memory false reports in the follow-up interview. Fig. 2. Results from Experiment 1: mean misinformation-consistent Misinformation task. We first analyzed correct mem- response (MCR) and false memory rates in participants who had slept ory by calculating the rate of correct responses to non- 5 or fewer hours the night before (restricted-sleep group) and those who had slept more than 5 hr (reference group). Error bars represent critical questions (i.e., questions that were not related to ±1 SEM. the misinformation given in the misinformation phase). The correct-memory rate did not differ significantly between the restricted-sleep group (M = 87%, SD = 19%) information, and answered a battery of personality ques- and the reference group (M = 89%, SD = 15%), t(191) = tionnaires (unrelated to the present research). They were 0.7, p =.5. The correct-memory rates were rather high, also given instructions about how to complete a brief sleep and the null result may have been due to ceiling effects diary each morning for the following week. Each day, they on performance (see the Supplemental Material for addi- were to report the time they got in bed, the length of time tional analyses). it took them to fall asleep, the time they awoke, the time Next, we examined misinformation-consistent response they got out of bed, and the number and duration of awak- (MCR) rate—participants’ tendency to incorporate infor- enings during the night. Research staff reminded partici- mation from the narratives into their responses to critical pants to complete their sleep diaries each morning. questions. The restricted-sleep group incorporated the Exactly 1 week after the preliminary session, partici- misinformation into their responses 38% of the time (SD = pants returned for the study session. They first saw the 30%), whereas the reference group did so only 28% of the two sets of photographs for the misinformation task (i.e., time (SD = 25%). This difference narrowly missed signifi- the event-encoding phase). Next, they completed the cance, t(191) = 1.9, p =.06, Cohen’s d = 0.27 (Fig. 2). questionnaire containing the news-event item. Immediately Finally, we compared false memory rates between the afterward, they completed another questionnaire battery two groups. We calculated the percentage of critical ques- unrelated to the present research. Then, they viewed the tions for which participants both chose the misinforma- misinformation narratives, which were followed by more tion-consistent response on the forced-choice test and personality questionnaires. Participants then completed reported that they remembered seeing the misinformation the testing phase of the misinformation task. Finally, they in the photographs (i.e., by indicating in the source test underwent the in-person interview and were debriefed. that they saw the information “in the pictures only” or “in both [the pictures and the narratives] and they were the same”). The sleep-restricted group selected misinforma- Results tion-consistent responses and attributed those responses In order to assess whether restricted sleep was associated to the photographs 18% of the time (SD = 20%), and the with false memory, we divided participants into two more rested group did so 13% of the time (SD = 17%). groups on the basis of their self-reported sleep duration This difference was not statistically significant, t(191) = on the night prior to the study session. Participants 1.35, p =.18 (Fig. 2). reported an average of 6.8 hr of sleep (SD = 2.0), and 28 participants (15%) reported 5 or fewer hours of sleep. We Discussion coded these participants as having restricted sleep.2 The remaining 165 participants (85%) were used as our refer- These findings tentatively suggest that restricted sleep is ence group. The two groups did not meaningfully differ related to memory suggestibility. However, we did not Downloaded from pss.sagepub.com at Universiti Teknologi MARA (UiTM) on July 18, 2014 Sleep Deprivation and False Memories 5 experimentally manipulate the amount of sleep partici- Participants assigned to the sleep condition were given pants had, and because the entire misinformation proce- from midnight until 8:00 the following morning to sleep, dure was completed following restricted sleep, we were whereas those assigned to the sleep-deprivation condi- unable to examine when during the formation of false tion were kept awake throughout the night. Neither memories restricted sleep had its influence. For example, group was allowed to consume caffeine. To ensure that restricted sleep may have impaired encoding of the event participants in the sleep condition slept on the night of (cf. Yoo, Hu, Gujar, Jolesz, & Walker, 2007), rendering the study, we used polysomnographic recordings, includ- those memories vulnerable to distortion. Alternatively, ing electroencephalography recordings on the scalp (at restricted sleep could have affected processes occurring F3, F4, C3, C4, O1, O2, with reference electrodes at M1 at the later stages in the misinformation procedure (i.e., and M2), electrooculography recordings on both eyes, retrieval). With this issue in mind, we designed an experi- and electromyography recordings on the chin and legs. ment to measure the effect of 24 hr of total sleep depriva- We also used electrocardiography to monitor heart rate, tion on susceptibility to false memories. We also thoracic and abdomen belts to monitor respiratory effort, manipulated time of encoding: In one condition, all three nasal cannulae to monitor respiration, and pulse oxime- stages of the misinformation procedure were conducted try to monitor oxygen saturation. Data were collected after sleep deprivation. In another, participants encoded using Embla N7000 recording systems (Embla ResMed, the photographs in a rested state but completed the mis- Denver, CO). Participants in the sleep-deprivation condi- information and test phases after a period of sleep tion were permitted to watch movies, play games, or deprivation. work on their computers but were not permitted to nap or engage in any physical exercise. Throughout the night, they completed the PANAS and SSS every 2 hr and were Experiment 2 offered a small, carbohydrate-rich snack every hour (to Method reduce the stress associated with sleep deprivation). Two research assistants who napped earlier that day moni- Participants. We recruited 104 Michigan State Univer- tored participants continuously throughout the night. sity undergraduates for participation in this study.3 Par- At 8:00 a.m., all participants were given breakfast. At ticipants had a mean age of 19.2 years (SD = 1.3; 54% 9:00, all participants completed the PANAS and SSS. The female, 46% male) and were native English speakers who participants in the morning-encoding condition then com- were not taking any medications that affected sleep. We pleted all three stages of the misinformation procedure, as included only participants who slept regularly (a mini- described in Experiment 1, and participants in the mum of 6 hr per night) in the week preceding the experi- evening-encoding condition completed the remaining ­ ment. Participants refrained from consuming alcohol or two phases of the study—misinformation and test. caffeine for 24 hr prior to the experiment; although they slept as usual the night before, they did not take any naps during the 24 hr prior to the experiment. Results Memory. For each participant, we calculated a correct- Design and procedure. The experiment used a 2 × 2 memory score, MCR rate, and false memory rate. We between-subjects design (see Fig. 1b). The independent examined the data using 2 × 2 analyses of variance with variables were sleep condition (8 hr sleep or sleep depri- sleep condition (sleep, sleep deprivation) and time of vation) and time of encoding (morning or evening). Par- encoding (morning, evening) as between-subjects fac- ticipants were blind to condition prior to arriving at the tors. For correct memory, we found no main effect of lab; they were told that they might sleep or remain awake encoding time, F(1, 99) = 0.79, p =.38. There was a trend at the lab and to be prepared for either. for correct-memory scores to be lower for sleep-deprived Participants arrived at the lab at 10:30 p.m. and com- participants than for rested participants, but the main pleted measures of mood, sleepiness, and working mem- effect of sleep condition did not reach significance, F(1, ory capacity: the Positive and Negative Affective Schedule 99) = 3.08, p =.08. There was not a significant interaction (PANAS; Watson, Clark, & Tellegen, 1988), the Stanford between the factors, F(1, 99) = 0.55, p =.46. Sleepiness Scale (SSS; Hoddes, Zarcone, Smythe, Phillips, For MCR rates, there were no main effects of either & Dement, 1973), and the Operation Span (OSPAN) task sleep condition, F(1, 99) = 0.15, p =.70, or encoding (Turner & Engle, 1989). Immediately after these tasks, time, F(1, 99) = 1.70, p =.20. However, there was a trend participants in the morning-encoding condition were for an interaction between the factors, F(1, 99) = 3.02, assigned to either sleep or remain awake, and partici- p =.09. In the morning-encoding condition, MCR rates pants in the evening-encoding condition completed the were marginally higher after sleep deprivation than after encoding phase of the misinformation procedure and sleep, but no differences emerged in the evening-­ were then assigned to either sleep or remain awake. encoding condition. Downloaded from pss.sagepub.com at Universiti Teknologi MARA (UiTM) on July 18, 2014 6 Frenda et al. Deprived Table 1. Mean Duration of Total Sleep Time and Each Sleep Rested Stage for Participants in the Sleep Condition of Experiment 2 0.5 Morning-encoding Evening-encoding Measure condition condition 0.4 Total sleep time (hours) 7.21 (0.46) 7.11 (0.67) NREM 1 (minutes) 24.6 (13) 28.8 (12) False Memory Rate NREM 2 (minutes) 216.5 (31) 189.1 (41) 0.3 NREM 3 (minutes) 106.5 (26) 131.7 (36) REM (minutes) 85.5 (29) 76.8 (32) 0.2 Note: Standard deviations are given in parentheses. 0.1 either model (ps >.5) and no interactions (all ps >.10). These results suggest that the effects of sleep deprivation 0 and encoding time did not depend on working memory Morning Encoding Evening Encoding capacity. Fig. 3. Results from Experiment 2: mean false memory rates of rested and sleep-deprived participants in the two encoding conditions. Error Sleep. All participants slept at least 6 hr on the night of bars represent ±1 SEM. the study. Table 1 presents the mean duration of each sleep stage, separately for the two encoding conditions.4 Next, we compared false memory rates. We found no main effect of sleep condition, F(1, 99) = 0.54, p =.46, or General Discussion encoding time, F(1, 99) = 3.12, p =.08. However, there was a significant interaction between the factors, F(1, We investigated the effect of reduced sleep and total 99) = 4.52, p =.04. Planned comparisons revealed that in sleep deprivation on susceptibility to false memories. the morning-encoding condition, the false memory rate Experiment 1 provided initial evidence that restricted was significantly higher in the sleep-deprived group than sleep is associated with increased false memory. in the rested group, t(51) = 2.01, p =.04 (two-tailed), Participants who reported 5 or fewer hours of sleep the Cohen’s d = 0.56. However, in the evening-encoding con- night before the experiment were more likely to report dition, there was no significant difference in the false that they had witnessed a news event that they did not memory rate between sleep-deprived and rested partici- actually see, compared with rested participants. There pants, t(52) = 0.98, p =.33 (Fig. 3). (See the Supplemental was also a trend for these participants to incorporate Material for additional analyses not reported here.) more misleading information into their memory for visual materials. In Experiment 2, the sleep-deprived group Mood and sleepiness. We also examined participants’ showed greater susceptibility to false memories relative sleepiness and affect. As expected, sleep-deprived par- to the rested group, but only when participants were ticipants reported significantly higher morning sleepi- sleep deprived during all three stages of the misinforma- ness, and lower positive affect, relative to rested tion procedure. When participants encoded the original participants, ps <.001, but there was no association event in a rested state, there were no discernible differ- between morning sleepiness and MCR rate, r(88) =.05, ences in false memory between participants who were p =.62, or false memory rate, r(88) =.02, p =.83. Simi- rested and those who were sleep deprived during misin- larly, there was no association between morning positive formation and test. affect and MCR rate, r(91) =.03, p =.80, or false memory Why were sleep-deprived participants more likely rate, r(91) = −.04, p =.74 (see the Supplemental Material than rested participants to fall sway to our suggestions in for group means and statistics). the morning-encoding condition, but not in the evening- encoding condition? One possibility is that sleep depriva- Working memory capacity. Finally, we tested whether tion increased false memories by influencing processes working memory capacity (measured by the OSPAN task) related to encoding. Sleep deprivation may have impaired predicted susceptibility to MCR or false memory. We used encoding of the original event, thus making memory two multiple regression analyses, one predicting MCR more vulnerable to intrusions from misleading postevent rate and one predicting false memory rate. For each, we information. This possibility is also supported by the entered sleep condition, encoding time, and OSPAN trend for decreased correct memory after sleep depriva- scores as predictors, followed by interaction terms. We tion in the morning-encoding condition and is consistent found no main effects of working memory capacity in with previous research showing that sleep deprivation Downloaded from pss.sagepub.com at Universiti Teknologi MARA (UiTM) on July 18, 2014 Sleep Deprivation and False Memories 7 reduces the ability to encode new information (Yoo et al., Author Contributions 2007). K. M. Fenn, S. J. Frenda, L. Patihis, and E. F. Loftus developed In the evening-encoding condition, memories of the the study concept and contributed to the study design. Testing photographs could have been affected by consolidation and data collection were performed by L. Patihis and S. J. processes in participants who slept. In other words, Frenda (Experiment 1) and by K. M. Fenn and H. C. Lewis sleep-deprived participants in the evening-encoding con- (Experiment 2). S. J. Frenda and L. Patihis performed the data dition were different from the rested participants in two analysis and interpretation under the supervision of K. M. Fenn ways: They were in a state of deprived sleep, and they and E. F. Loftus. S. J. Frenda and K. M. Fenn drafted the manu- also did not have an opportunity to consolidate memory script, and all authors provided critical revisions. All authors approved the final version of the manuscript for submission. for the photographs. Thus, any comparison of rested and sleep-deprived participants in the evening-encoding con- Declaration of Conflicting Interests dition must be interpreted with caution. This issue not- withstanding, it is important to note that we observed a The authors declared that they had no conflicts of interest with difference in false memory rates between rested and respect to their authorship or the publication of this article. sleep-deprived participants only in the morning-­encoding condition, wherein participants could not have consoli- Supplemental Material dated memories of the photographs during sleep. Additional supporting information may be found at http://pss Our results also suggest that total sleep deprivation.sagepub.com/content/by/supplemental-data may not be necessary to increase false memory. Restricted sleep may also increase the risk of false memories. In Notes Experiment 1, a night of short-duration sleep was associ- 1. One exception is a unique study (Blagrove, 1996) showing ated with a trend toward higher rates of claiming to have that sleep-deprived participants were more likely than rested seen nonexistent video footage of a news event that participants to yield to leading questions about a story they had occurred many years prior to the experiment. Previous read. In that study, however, the sleep-deprived participants research has suggested that false memories of witnessing were tested at a different circadian time than the rested partici- news events may emerge when imagined events are con- pants, a serious confound that limits conclusions that can be fused with actual memories (see Ost et al., 2002; also see drawn. Furthermore, it is unclear whether the findings indicate Garry et al., 1996; Lindsay, 2008). In the present study, that sleep deprivation increased memory distortion per se or merely increased acquiescence to leading questions. restricted sleep was associated with an increased likeli- 2. Previous studies have shown that sleep restricted to 4 to hood of false memories of an event that had long since 6 hr for several nights can impair cognitive functioning (cf. passed, which suggests that reduced sleep may impair Axelsson et al., 2008; Dinges et al., 1997; Van Dongen, Maislin, the accuracy of source judgments at retrieval. Mullington, & Dinges, 2003). Although some studies have On the whole, sleep deprivation appears to increase shown that 6 or fewer hours of sleep per night over several the risk of false memories. However, sleep deprivation nights can cause cognitive deficits (e.g., Van Dongen et al., may affect the development of false memories differently 2003), we chose a more conservative measure of sleep restric- depending on the procedure or testing method. In a mis- tion because we were investigating the effects of only a single information procedure, sleep deprivation increased false night of restricted sleep. memory, but only when participants were sleep deprived 3. One participant had difficulty sleeping in the laboratory and for all three stages of the procedure (including encod- did not complete the experiment. 4. Because of equipment failure or experimenter error, sleep ing). For false memories of witnessing news events, sleep data from 4 participants (1 in the morning-encoding condition restriction may impair source accuracy at retrieval. In the and 3 in the evening-encoding condition) could not be analyzed. DRM paradigm, there is some evidence that sleep depri- vation at retrieval may increase false memory in recogni- References tion testing (Diekelmann et al., 2008) but not recall testing (Diekelmann et al., 2010). 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