CogBlog – A Cognitive Psychology Blog

According to the National Sleep Foundation, adults need seven to nine hours of sleep a night. Sure, we all know sleep is important for our health, but life always seems to intervene and these ideal seven to nine hours turn into four to five hours. Lacking sleep like this may make many of us feel tired and irritable, but we often fail to recognize how it may impact our memory for a day’s events. Sleep deprivation makes it tougher to remember things, such as witnessing a car accident or remembering a friend’s story. It is even possible for it to cause us to make up memories for events that never happened!

Researchers Frenda, Patihis, Loftus, Lewis, and Fenn (2014) strived to investigate this and conducted a combination of experiments about sleep deprivation’s effect on false memories. False memories are memories of an event that either occurred differently from how you remember it or never occurred at all. These can be as extreme as believing you have a memory for visiting a city you never did or as mundane as construing a memory for a video you have never seen before. Making up memories like this can yield dire consequences, especially with eyewitness testimonies where an individual may be wrongfully charged because of a witness’ false memory. However, can a lack of sleep make this more likely to happen?

This psychological study had two, similar experiments. In the first experiment, participants kept a sleep diary and were divided into two groups, one labeled as sleep deprived, or those who got an average of five or fewer hours of sleep, and normal, for those who got six or more hours of sleep. During the experiment itself, participants completed two tasks to determine their rates of false memory. The first was about a news event, where participants answered “yes” or “no” to seeing a video of the plane crash in Shanksville, Pennsylvania from 9/11 (if you want to learn more about vivid, and sometimes false, memories for tragic events, click here for an enlightening blog post!) In reality, this video is nonexistent, so saying “yes” would indicate a false memory. In addition to responding to this on a questionnaire, the experimenters also interviewed participants and obtained a verbal “yes” or “no”. The second task to measure participants’ false memory was something called a misinformation task. Here, participants briefly saw two sets of photographs, each containing pictures depicting a man stealing a car and a woman having her wallet stolen. After seeing these pictures, participants read texts about the plots from the photographs. However, within these texts, there were sentences that contradicted the information portrayed in the pictures, hence the task’s name: misinformation. To measure false memory, the participants took a memory test that questioned specific events from the photographs. Answering these questions incorrectly would indicate false memories, as it would mean that the participants incorporated the false information from the texts into their memories of the photographs.

In the first experiment, participants classified as sleep deprived condition were more likely to say “yes” to seeing the nonexistent video on the questionnaire. However, getting sleep or not did not make participants more likely to say “yes” when instructed to verbally provide their answers. These findings suggest limited sleep may make one more likely to construe false memories, especially when answering it more passively on a questionnaire compared to actively giving a verbal response. As for the misinformation task, the sleep deprived group was slightly more likely to answer critical questions incorrectly, meaning that they mixed the contradictory information from the texts into their overall memories of the photographs, and fell victim to developing false memories. However, these results were weak, so it is possible that sleep did not increase the false memories.

Due to this dilemma, the experimenters developed a second experiment. They used the same misinformation task as in experiment one and nixed the news task. However, they had control over how much sleep participants received by randomly assigning them to get a full eight hours of sleep in the lab or making them stay up all night. The experimenters also wondered whether the amount of sleep participants had while obtaining the information would affect the development of false memories. Thus, they created evening and morning encoding conditions to separate when participants obtained information from when they had to retrieve it. In the evening condition, participants, both those able and unable to sleep, saw the photographs at night, but read the texts and took the memory test the next morning. So here, the researchers were curious if sleep deprivation negatively affected participants’ memory, even if the information was obtained well rested. As for the morning condition, participants completed the entire study the morning after, with zero or eight hours of sleep. In this condition, the researchers wanted to see if encoding the information while sleep deprived affected memory. It is important to note that there was a difference in time for remembering this information, as participants tested in the morning only had to remember it for a brief period of time, but those given the information in the evening had to remember it for the entire night. This difference was not the researchers’ focus and there were no differences in false memory rates between the morning and evening conditions for those with eight hours of sleep.

In this experiment, the participants who slept zero hours had higher rates of false memory when they completed the entire study the morning after. There was no increase in false memories for either sleep conditions when the pictures were shown the night before. These results suggest that when we process the information rested, we will be able to keep the facts straight, but when deprived of sleep during processing, it will be easier to develop false memories.

With results like these, we can add to the large list of why sleep is important. As seen in the first experiment, even a reduced amount of sleep increased participants’ chance of having false memory. Furthermore, the second experiment provided stronger evidence for sleep’s importance in processing and later retention of information. Students should take note of this and use this information to their advantage! If they are rested while studying all night, they will be more likely to remember the information correctly. Nonetheless, if they’re in the middle of midterms and haven’t had sufficient sleep all week, they may be more susceptible to confuse the necessary information and thus perform worse on an exam.

Developing false memories in such a manner also relates to other psychological concepts, such as suggestibility and misinformation. Suggestibility is adding and/or including incorrect information to an original memory, which was directly seen in this study when participants added the inconsistent information from the texts into their memory of the pictures. Similarly, misinformation is remembering a memory incorrectly because of how the information is presented. In the context of the described study, misinformation could occur if participants were asked “How did the man approach the woman when he snatched her purse?” vs. “How did the man approach the woman when he took her purse?” If the participants saw the sentence with “snatched”, they may be more inclined to think he took it quickly, and thus say he ran or quickly walked up to her, even if this was not true. This study suggests that suggestibility is more likely to happen when deprived of sleep. However, it would be worthwhile to further delve into this and see if misinformation is also more likely to occur with sleep deprivation!

If you want to learn more about sleep’s effect on memory, check out this blog post!

References:

Frenda, S., Patihis, L., Loftus, E., Lewis, H., & Fenn, K. (2014). Sleep Deprivation and False Memories. Psychological Science, 25, 1674-1681. doi:10.1177/0956797614534694

How Much Sleep Do We Really Need? (n.d.). In National Sleep Foundation. Retrieved November 22, 2015. From https://sleepfoundation.org/how-sleep-works/how-much-sleep-do-we-really-need