The Effect Sleep Has on Short-term Memory


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It is recommended that an average person gets approximately 8 hours of sleep every night to ensure the body and brain recover from the previous day and remains healthy. However, it is reported that students are getting far less than the recommended amount at about 6.5 hours a night. There are several factors as to why students specifically do not meet the recommended target each night including stress, workload, and lacking structure in their life. Memory is a vital skill for a student as they are often having to remember facts and figures amongst other pieces of information when sitting examinations. This report will look at an experiment set up to test whether sleep can have an impact on short-term memory.

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Hypothesis: If the amount of sleep is related to short-term memory, then the more sleep a person gets will result in an improvement in short-term memory.

8 participants were involved in this study; all of which were male, aged between 20-22, and students.

The 8 participants were randomly split into 2 groups: the control group and the experimental group. The 4 participants in the control group could sleep for 9 hours on a specific night and the 4 participants in the experimental group were only allowed to sleep for 3 hours on the same night; a 1/3 of what the other group was sleeping. Both groups were told they must wake up at 10 am and therefore adjust when they’re allowed to sleep accordingly i.e. a person from the experimental group could only go to sleep at 7 am.

The morning after members from both groups slept for their specific time, all participants came together. They were instructed to wait outside a room and that 2 participants would be called in at a time: one from each group. Participants sat at either end of a long table and were presented with a list of 25 words. Each list contained the same words in the same order. They were instructed that they had 2 minutes to try and remember as many words as possible. After the 2 minutes were up, the list was removed from each participant and then instructed to write down as many words as they could remember. Again, they had 2 minutes to do this. This was done for every participant in the study.

There were many characteristics of the experiment which were well designed. Firstly, the use of a control group that could sleep for a normal amount of time (more than the minimum recommended amount) allows for the results of the experimental group to be compared.

Having control in the experiment ensured the reduction of many extraneous variables. It also ensures that the experimental study does not become confounded.

Furthermore, randomization was used to split the participants into either group. This was done completely at random and no information about the participants was considered when deciding their group. Each member had an equal chance of ending up in either group. This means that any effects from extraneous variables should be distributed somewhat evenly. The list of words given was also completely random – created from a word generator. This list was the same for both groups.

All individuals who took part in the study were entirely independent and had no conflict of interest whatsoever.

Although the sampling size of the experiment was small due to only having 8 participants, the population of the study was all very alike. This further explores the idea that no outside variables should have much of an effect on the study. For example, if there was a participant who varied in age by 50 years there are likely other factors (that may only affect them due to age) that must be considered when analyzing their results.

On the contrary, there were some features of the experiment which could be considered as pitfalls. To begin with, there was no placebo or blinding (or double/triple blinding) involved in this experiment. This is due to the researcher believing it would not have any effect on results taken at the end and there was no reason to include either in this type of study.

Also, as previously mentioned, the number of participants was very few. Although the specification given stated 10 would be enough – and 8 not being far off that – in the grand scheme of things, this sample size is likely, not big enough. Having a small sample size means that it becomes less representative of the entire population. This could further lead to types of selection bias.

To future-proof this experimental design, the conditions of the experiment can be seen in full alongside how the randomization and control groups were set up. This should allow for results to be reproducible.

Independent Variable: Hours of sleep.

This is the variable that the researcher had control over. So, for the control group, they can sleep for 9 hours whilst the experimental group was only allowed to sleep for 1/3 of this. This is the variable that gets manipulated to find out the value of the dependent variable and allow conclusions to be drawn from this.

Dependent Variable: Number of words remembered from the list

This is the variable being measured in this experiment. The idea is that as the hours of sleep change, so will the number of words remembered from the list. This variable depends on the independent variable.

Control Variable(s): List of words, order of words, time of day participants must wake up, time participants had to remember words, time participants had to write down words, and time of day participants performed the second part of the study the morning after (remember/write words).

Failing to have control over certain variables in the study would have left it susceptible to being invalid. Ideally, both groups should be as similar as possible with the only real exception being the independent variable which, in this case, is the hours of sleep. Therefore, all the control variables are kept constant throughout for both groups. Having control variables means that the relationship between the independent and dependent variables is clearer as there are fewer other factors involved.

Causal: If the amount of sleep is related to short-term memory, then the more sleep a person gets will cause an improvement in short-term memory.

Null: There will be no improvement or a deterioration in short-term memory if a person gets more sleep.

Alternative: There will be an enhancement in short-term memory as a result of increased hours of sleep.

As sleep is an extremely vital part of a human’s lifestyle which aids in them maintaining optimal health, it can be assumed that if a person sleeps more, they will perform better the next day. Previous research shows that sleep is good for the brain, and therefore the assumption was made that more sleep will result in better short-term memory.

Premise 1: Most participants in the control group remembered more words from the list than participants of the experimental group.

Premise 2: All participants of the study were male students.

Conclusion: Therefore, most male students would probably have an improvement in short-term memory if they slept for 9 hours a night rather than 3 hours.

This argument is inductively strong as if the two premises are true, then it is highly probable that the conclusion is also true as well. Furthermore, there is no hasty generalization made and very little bias from the sample. However, although the argument is inductively strong, it is not cogent. Cogent refers to an argument being logically strong and has truth in its premises. This argument does have logical strength, but it does not have all true premises.

Premise 1: The average of words remembered by the control group was greater than the average of the experimental group

Premise 2: The experimental group’s average was less than 13.

Conclusion: Therefore, the average of words remembered by the control group was greater or equal to 13.

This is a valid argument as if the two premises are true, then the conclusion that follows must be true as well – meaning this argument has validity. A valid argument cannot have true premises but a false conclusion. Not only in this case are the two premises and following conclusion true, but they are both logically strong. Furthermore, this argument is also sound as not only is it valid, but it also has true premises.      

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