The Influence of Sleep on Memory

Transcription

1 The Huron University College Journal of Learning and Motivation Volume 48 Issue 1 Article The Influence of Sleep on Memory Andrew Soave Follow this and additional works at: Part of the Psychology Commons Recommended Citation Soave, Andrew (2010) "The Influence of Sleep on Memory," The Huron University College Journal of Learning and Motivation: Vol. 48 : Iss. 1, Article 10. Available at: This Article is brought to you for free and open access by the Psychology at Scholarship@Western. It has been accepted for inclusion in The Huron University College Journal of Learning and Motivation by an authorized editor of Scholarship@Western. For more information, please contact tadam@uwo.ca, wlswadmin@uwo.ca.

2 Sleep and Memory 263 The Influence of Sleep on Memory Andrew Soave Huron College The purpose of the current report was to determine if sleep could affect the recall of word pairs, f'articipants were 24 students from the University of Western Ontario and its affiliate campuses. Participants were given 8 concrete or abstract word pairs and were tested on the word pairs 12 hours later. Participants filled this time with either sleep or by being awake. The results of the study showed that there was no significant interaction between sleep or awake conditions with concreteness on recall F(l,20) = 1.76, p >.05, n.s. This study concludes that sleep did not effect the recall of word pairs, which differs from the results of past research. The influence that sleep has on memory is still unclear in many research studies. Gais, Molle, Helms and Bom (2002) performed a study were they monitored the different EEG activity in the brain while participants were asleep. In specific, they were looking at the formation of sleep spindles during sleep. The participants in the study stayed in a sleep laboratory for three nights and during these three nights the participants were attached to the EEG (Gais et al, 2002). Before falling asleep on one of the two nights the participants learned a set of word lists and were tested on this set after the leaming task was finished and 30 minutes after they awoke the next morning (Gais et al, 2002). Participants also took part in a non-leaming task on the other night, and this was done to compared the difference EEG results between a leaming and non-leaming task. The results of the study showed that when participants slept after the learning task, they had a higher density of sleep spindles than those in the non-learning task (Gais et al, 2002). This indicates that something occurs during sleep, and these sleep spindles could

3 Sleep and Memory 264 represent memory consolidation (Gais et al, 2002). However, since it is a correlation study it cannot prove anything, but it does highlight that there is some biological aspect to the relationship between sleep and memory. Other researchers have tried to measure the influence of sleep has on memory by using recall instead of sleep spindles. Stickgold, Whidbee, Schirmer, Patel and Hobson (2000), compared awake participants' recall to those that were asleep on a visual recognition task. The results of the study showed that participants that received more than 6 hours of sleep outperformed participants in the awake group (Stickgold et al, 2000). They also found that if the participant did not get more then 6 hours of sleep, they would not improve on the task. Stickgold et al. (2000) found that the longer the participant slept, the better they performed on the recognition task. Payne, Schacter, Propper, Huang, Wamsley, Tucker, Walker and Stickgold (2009) performed a study where they compared the recall of participants who were in a sleep group, to participants that were in an awake group. Participants recalled words which they heard from a tape recording, and they learned the words at either 9am or 9pm and were tested on them 12 hours later. The results of the study showed that participants in the sleep condition recalled more words than participants in the awake condition (Payne et al, 2009). However, there was another interesting result; the study showed that participants in the sleep condition also recalled more false words than those in the awake condition. Both of these studies support that sleep participants perform better than awake participants on recall. Some researchers have looked at how to enhance specific tasks by using particular periods of sleep. Plihal and Born (1997) performed a study comparing memory in participants that had more short wave sleep (SWS) or rapid eye movement (REM) sleep.

4 Sleep and Memory -^"0 The participants had to complete two different tasks. The first task was a paired associate task, and the second task was a mirror tracing task. Participants were in one of four groups, early sleep which tested SWS, early awake, late sleep which tested REM sleep and late awake. The results of the study showed that participants who received more SWS did better on the paired associate task, conversely participants in the REM sleep group performed better on the mirror tracing task (Plihal & Born, 1997). Both of these groups of participants performed significantly better then the awake participants. Wagner, Gais, and Born (2001) also compared recall of participants who were in two different sleep groups a REM and SWS group, to an awake group of participants. The participants had to memorize a set of text, that was either emotional or neutral. The results of the study showed that both the REM sleep group and the SWS group outperformed the awake participants (Wagner et al, 2001). However, the REM group performed better when compared to the SWS group. Recall may be influenced by the individual task. Researchers have also studied participants' recall while they have been awake, without any sleep condition. Paivio (1965) performed a study in which he measured what set of words participants could remember better, concrete or abstract words. The study had participants tested on four different sets of word pairs that were either all concrete words, all abstract words, or concrete and abstract words. Paivio (1965) found that the abstract words were the hardest to remember, while the concrete words were the easiest to remember. He attributed this to the amount of imagery that each word had associated with it. Paivio, Yuille, and Madigan (1968), tested this hypothesis further by measuring concreteness, imagery, and meaningfulness in 925 words. The participants in the study rated the different words on the three different measures across two different days. Paivio

5 Sleep and Memory 266 et al, (1968) found that words that were high on imagery were also high on concreteness and this seemed to define a common dimension. The Paivio (1965) study shows that words that are high in concreteness are easier to recall than words low in concreteness, or abstract words. Jenkins and Dallenbach (1924) performed a study in which they compared the recall of participants who were awake or slept for 1, 2, 4, or 8 hours. Participants had to memorize non-sense syllables and then they were tested on their ability to recall as many syllables as they could remember. The participants filled the time between testing and leaming by either sleeping or going about their normal day. The results of the study showed that participants in the sleep condition recalled more words than those in the awake condition (Jenkins and Dallenbach, 1924). The biggest difference of recall occurred in the 8 hour condition, where the participants in the sleep condition greatly out performed participants in the awake condition. This study supports that the longer a participant sleeps, the better their recall will be. The current study is testing whether sleep will have an influence on memory. Previous research has supported that sleep can influence recall (Jenkins and Dallenbach, 1924; Plihal & Bom, 1997; Payne et al, 2009). The current study will used the design from the Jenkins and Dallenbach (1924) study, but instead of using non-sense syllables the word pairs from the Paivio (1965) study will be used. The current study should show that participants in the sleep condition will recall more word pairs than those in the awake condition, with both the concrete and abstract word pairs. Concrete word pairs should also be easier to recall than abstract word pairs.

6 Sleep and Memory 267 Method Participants Participants were recruited from the University of Western Ontario and its affiliated campuses. The age range of the participants' age was between 18 and 24, there were 24 participants in total, 9 were male, and 15 were female. Participants were most likely from the middle to upper socio economic class. The participants were all in different years of university. Materials The study used two different word lists that either consisted of 8 concrete word pairs or 8 abstract word pairs. Please refer to appendix B, for the word lists used for both the concrete and abstract word pairs. These word lists were taken from the Paivio (1965) study, in which he used the word pairs to test recall. The lists were divided into concrete or abstract based on the amount of imagery which they could be associated with (Paivio, 1965). For the concrete word pairs pencil (7.70) and tree (6.77) had the highest concreteness and imagery ratings respectively (Paivio, 1968). Woman (6.63) and string (6.20) had the lowest concreteness and imagery ratings respectively (Paivio, 1968). For the abstract word pairs, series (3.88, 4.47) had the highest concreteness and imagery ratings, while idea (1,42) and soul (2.13) had the lowest concreteness and imagery ratings respectively (Paivio et al, 1968), The measures of the concreteness and imagery ratings showed that there was high criterion validity with the Paivio et al, (1968) study. However, there was no measure of reliability for the word pairs.

7 Sleep and Memory 268 Procedure Participants were randomly assigned into one of four possible conditions, awake abstract, awake concrete, sleep abstract or sleep concrete. The random assignment was done by flipping a coin to determine which condition the participant was assigned to, and the coin tossing was done before participants were recruited. Participants in the awake condition performed the memorization phase during the morning, and then performed the testing phase 12 hours later at night. Conversely, participants in the sleep condition took the memorization task at night, and then took the test in the morning 12 hours later. This was done to ensure that the participant would get some sleep between the memorization phase and the testing phase. The participants in the abstract condition were given the abstract word pairs, while participants in the concrete condition were given the concrete word pairs. Participants would first read over the letter of consent, and then give their consent to participate in the study. Depending on what number the participant was, it determined which condition he or she would be put into by the previous random assignment. The participant would then be given the word list and told to memorize it. The participant was tested on the word list after he or she had felt he or she had memorized it. This was done to ensure that this list was actually memorized before the testing phase. During this stage the participant had unlimited time to memorize the word list, but the participant had to say the list verbally twice without looking or without any errors before they could move on to the testing phase of the study. The researcher would test the participant by asking them to fill in the missing word from each pair, and this was done by stating the first

8 Sleep and Memory 269 word of each pair and having the participant state the second word in the pair. After the participant had completed the memorization task, the researcher noted the time the phase was completed and told the participant that 12 hours later they would be tested on Facebook using the same word pairs. The participant was released from the study and carried on with their day or night. The researcher sent a message on Facebook to the participant giving them the instructions to open the message at the specified time the participant was told after the memorization phase. Once the participant opened the message, they were given instructions to fill in the missing word pairs, and if they did not know what to put, they were to leave it blank or guess. After they were done, they were told to send it back to the researcher and then the participant would be given the debriefing form. During this testing phase, a different set of words was taken away. Please refer to appendix B to see which words were missing. Five words from the first column remained, while only 3 words from the second column remained. This was the same for both conditions, and this was done to keep consistency. Participants were blind to which conditions they were in. Results A 2 X 2 between-subjects ANOVA was performed on the dependent variable recall and the two independent variables concreteness and sleep/awake conditions. The results showed that there was no significant main effects for concreteness F(l,20) = 2.91, p >.05, n.s. with participants who learned the concrete word pairs (M = 7.5, SD = 0.8) or the abstract word pairs (M= 6.75, SD = 1.36). There was also no significant main effect for the sleep/awake conditions F(l,20) = 1.76, p >.05, n.s. with participants in the sleep condition (M= 7.42, SD =.79) or participants in the awake condition (M= 6.83, SD =

9 Sleep and Memory ). There was also no significant interaction between concreteness and sleep/awake on recall F(l,20) = 1.76, p >.05, n.s. As figure 1 shows, participants who had to recall the concrete word pairs, had the same means regardless if they were in the sleep and concrete condition. The lowest mean was in the abstract condition when participants were awake. Discussion Unlike previous research the current study failed to support that sleep had a significant influence on recall. The results showed no significant interactions or main effects. This is likely due to many methodological issues that are in this study. The first issue is about the recall task itself. There were some concerns that it would not be difficult enough, but since the testing phase involved a rather unique method of testing, it was assumed that difficulty would not be an issue. However, since that only two people recalled less than 6 out of 8 words and there were 13 scores of 8, the task did not prove challenging enough. This proved that the word list was not an appropriate measure and because of this it likely influenced the results of the study. In previous studies like the Jenkins and Dallenbach (1924) study, in the awake condition participants hardly remembered any non-sense syllables at the 8 hour interval, It was thought that since the interval was being increased to 12 hours, recall would be even worse. But this was not the case, and recall was much better in the current study than in the Jenkins and Dallenbach (1924) study. This could also be attributed to the different types of measures. Jenkins and Dallenbach (1924) used non-sense syllables, and this could have been more difficult to remember than actual words. Another problem with the study was the lack of control. After the participants had completed the leaming trial, the researcher could not stop the participant from writing

10 Sleep and Memory ~ ~ Sleep 6 ; Awake 5 ' o Concrete Word Pairs Abstract Figure 1. Shows the average number of words recalled for the sleep/concrete condition (n = 6), sleep/abstract condition (n = 6), awake/concrete condition (n = 6), and awake/abstract condition (n = 6).

11 Sleep and Memory 272 down the word pairs and consistently memorize them before they were tested again 12 hours later. While participants were separated during testing, they could have tried to talk to another participant in the study and compared answers. It was assumed that most participants would not do either of these things, however, there was no way to control for it. The final methodological issue was the difficulty of time. When the participants completed the learning phase, they were told that 12 hours later they had to answer the message on Facebook. Nevertheless, some participants would take the test 2 hours earlier or later than they were suppose to, and this data could not be counted. This happened on several occasions and the participants were still debriefed, but their data was not recorded. Another limitation of the study was the sample size and population. The sample size of the study was small and ideally researchers want 40 or more participants for a 2 X 2 ANOVA, to increase the likelihood of significant results. But unfortunately due to the demanding nature of the study, it was difficult to recruit participants into the study. Since participants in the study all went to university it could affect the results because university students, especially psychology students, are generally more knowledgeable about memorization strategies. The final methodological issue is the reliability of the measure. When Paivio (1965) used the same word pairs in the current study, he used a random set of words for every trial, so there was no measure of reliability in his study. There was also no reliability for the measure that was used in this study; this could have influenced the results of the study. The researcher should have tested the reliability of the measure before performing the study.

12 Sleep and Memory 273 Future studies should increase the word pair size to 12 concrete or abstract words instead of 8. When testing the participants, researchers should have six stimulus words using the first word in the word pairs, and six stimulus words using the second word in the pair. This should be done randomly, so it is just not an altering from first word to second every other trial. However, the overall pattem should be the same for each testing trial. These changes should increase the task difficulty of the measure. The researcher in future studies should test the reliability of the word pairs before using them, in order to ensure that it would be a reliable measure. Future studies should also get a bigger and a more varied sample population than the one in the current study. A different sample population would allow for more generalization to the normal population. Finally, if possible future studies should consider the use of a sleep lab or consider having participants nap for a certain period of time after testing. This would solve many of the control and methodological issues of the current study. The current study failed to reproduce the results of previous research on sleep and memory. Sleep did not significantly influence participant's recall of word pairs. This was likely due to the methodological issues of the study. Future studies should consider keeping a similar design but improving the measure and if possible make use of a sleep lab.

13 Sleep and Memory 274 References Gais, S., Molle, M., Helms, K., & Bom, J. (2002). Learning-Dependent Increases in Sleep Spindle Density. The Journal of Neuroscience, 22, Jenkins, J. G., & Dallenbach, K. M. (1924). Obliviscence During Sleep and Waking. American Journal of Psychology, 35, Paivio, A. (1965). Abstractness, Imagery, and Meaningfulness in Paired-Associate Leaming. Journal of Verbal Learning and Verbal Behaviour, 4, Paivio, A., Yuille, J. C., & Madigan, S. A. (1968). Concreteness, Imagery, and Meaningfulness. Journal of Experimental Psychology: Monograph Supplement, 76, Payne, J. D., Schacter, D. L., Propper, R. E., Huang, L., Wamsley, E. J,, Tucker, M. A., Walker, M. P., & Stickgold, R. (2009). The role of sleep in false memory formation. Neurobiology of Learning and Memory, 92, , Plihal, W., & Bom, J. (1997). Effects of Early and Late Noctumal Sleep on Declarative and Procedural Memory. Journal of Cognitive Neuroscience, 9, Stickgold, R., Whidbee, D., Schirmer, B., Patel, V., & Hobson, J. A. (2000). Visual Discrimination Task Improvement: A Multi-Step Process Occurring During Sleep. Journal of Cognitive Neuroscience, 12, Wagner, U., Gais, S., & Bom, J. (2001). Emotional Memory Formation Is Enhanced Across Sleep Intervals with High Amounts of Rapid Eye Movement Sleep. Learning and Memory, 8, Appendix A ANOVA Summary Table for Concreteness and Sleep/Awake Interaction with Recall Source SS df MS F P Concreteness A3 Sleep/A wake Concretness* Sleep/Awake Error Total Note; All numbers were rounded in order to keep with APA standards, of two decimal places.

14 Sleep and Memory 275 Appendix B Word List 1 String Coffee Shoes Pencil Wheat Women Chair Flower Tree Dress House Garden Potato River Magazine Star Word List 2 Idea Soul Effort Series Truth Fate Event Virtue Moment Opinion Freedom Health Duty Theory Fact History

15 Sleep and Memory Test 1 String Dress Shoes Pencil Potato Women Magazine Flower Test 2 Idea Opinion Effort Series Duty Fate Fact Virtue

16 Sleep and Memory 277 Appendix C Number of Words Recalled by Each Participant Conditions Concrete Abstract Sleep Awake Total words recalled 90 81