The Effect of Sleep on Cognition
Question: What is Sleep?
Maharishi: How can you know sleep when you are awake? The answer is to go to sleep to find out what it is.
Question: But I cannot know it in this way.
Maharishi: This question must be raised in sleep.
Question: But I cannot raise the question then.
Maharishi: So that is sleep. ( Sri Ramana Maharishi)
The function of sleep still remains a mystery. Much research has been conducted to find out the function of sleep and the effect that sleep deprivation or partial sleep deprivation might have on the waking life functioning. Some researchers have suggested that sleep is needed for the formation of long term memory (J. Zhang and others, 2004), and almost all sleep researchers agree that sleep is needed more for the brain than the body.
Much of the research is concentrated on sleep deprivation or partial sleep deprivation and the effect it has on cognition. As it would have been expected, most of the experiments suggest that sleep deprivation or partial sleep deprivation affects cognitive functions such as expressive speech, motor performance, complex arithmetic tasks, (J. Kim and others, 2001), mood (J. Pilcher, 1996). For example Professor Jim Horne and Dr. Yvonne Harrison of Loughborough University found that: 'sleep loss affects recovery of the frontal cortex of the brain. Lack of sleep impairs speech, memory and innovative, flexible thinking'.
We decided to see how sleep affects cognition on a day-to-day basis. By asking participants to complete a simple IQ questionnaire, we measured the time they took to complete it and the number of mistakes they made. The participants were then asked the number of hours they slept last night.
The findings are that there is a strong negative correlation between the number of hours slept and the number of mistakes. The correlation was slightly weaker with the time taken to complete the questionnaire. Therefore, the less number of hours the participant had last night, the more the number of mistakes they would make and it would take longer to complete the simple questionnaire.
The Research Hypothesis
We suggest that the more hours of sleep the participant has the less time would be needed to complete the questionnaire and less mistakes will be made.
Method
We browsed the internet to look at a range of IQ tests to get an insight on what they consist of. From this research we made an IQ test of our own which contained both easy and moderate questions to avoid any possible 'ceiling' or 'floor' effects. We also decided to have the critical question near the end to avoid the possibility of demand characteristics as much as possible. In addition we decided to administer the test during morning hours as we figured the brain gets more active or awake during the evening regardless of how many hours of sleep the participants had.
When handing out the questionnaire the participants were randomly approached, asked if they could spare some time to fill out the test and then timed (using a stopwatch) as they filled out the test. Participants were then debriefed about the study and told it was strictly anonymous. The dependant variable was the amount of sleep the participant had and the amount of incorrect questions. The sample consisted of 28 participants in which 18 were female and 10 were male. The age range was 14-46 however most were 18-20 year olds. All participants reside in the North West region and were chosen by an opportunity sampling method.
Results
A clear negative correlation was found between the hours of sleep and the number of mistakes made. The Pearson Correlation is r = -.780 with a probability of a mistake p= < . 001 in a thousand. The graph in Fig.1 clearly illustrates the relationship visually.
A negative correlative relationship was found between the hours of sleep and the time taken, r=-.598 and p= <.001. Here we see that it has taken more time to complete the questionnaire for a person who had 12 hours of sleep then for someone who had 10 as fig. 2 shows.
An interesting finding was also the fact that in our sample men in general slept about an hour more then women therefore obviously women made more mistakes in the questionnaire, as the bar chart below shows:
Discussion
After collecting the results, we inputted them into SPSS which allowed us to form a scatter graph and gave us a detailed statistical analysis. The line of best fit on the scatter graph (Fig.1) suggested that the 'hours of sleep' is negatively correlated to the 'number of mistakes' which suggest that the more hours of sleep you have the less mistakes you will make, thus it is safe to conclude that our hypothesis was proven correct. However the investigation did have some flaws, which were mostly due to extraneous variables. This could include demand characteristics, participants not recalling their sleep hours accurately and also questionnaires not filled out with full concentration due to distraction by peers, noise etc.
