Abstract The main outcomes of this study were that a significant (p<. 05) relationship was found between quality of sleep and subjective sleepiness, sustained attention and subjective mood. It was found that the better quality of sleep is obtained, the less subjectively sleepy, higher sustained attention and more positive subjective mood the participant has. The present study was in line with several other studies undertaken, with many of the findings being reflected in both this study and others. Limitation such as environmental factors and carryover effects may have the data.
Introduction Good sleeping patterns are an essential part of maintaining health, both physical and mental. Regular good sleep helps to consolidate memory, thus affecting cognitive performance, and also improves mood. Conversely, a poor nights sleep or irregular sleeping patterns have been shown to reduce cognitive performance, in ways such as reducing the ability to concentrate and affecting judgement (Taylor & McFatter, 2002). Taylor & McFatter conducted clinical trials concerning the affects of sleep on mental performance.
They concluded that ‘Sleep deprivation had an overall negative effect on accuracy in the time estimation, immediate recall, delayed recall, and digit span tasks’ thus determining that sleep affected participants did consistently worse on cognitive tasks compared to their well slept counterparts. Mood is also adversely affected by sleepiness (Oginska & Pokorski, 2006) with researchers concluding that 45% of participants experiencing fatigue due to an insufficient amount of sleep experienced irrational mood swings more frequently and also more irritability than participants who were well slept.
While there is much research stating the adverse affect of sleep deprivation, information concerning the positives of healthy sleep state that regular sleep in intervals of 7. 5 – 8 hours per night greatly enhance cognitive and motor functions (Ellenbogen, 2005). In his experiment, Ellenbogen compared motor and cognitive tasks of participants who had received approximetly 8 hours sleep before attempting the task compared to participants who had been awake for 12 hours. The esults demonstrated a strong (p<. 05) link between sleeping a better performance on these tasks. While there is strong evidence suggesting that sleep plays an important role in cognative performance and mood, the chronotype, that being morning orientated or evening orientated, of a person may play a larger role in cognitive performance and mood than sleep. Selvi, Gulec, Agargun & Besiroglu (2007) conducted an experiment to determine the affect of a person’s chronotype on cognitive ability.
They found that a person’s chronotype had a large influence on their performance, for example, participants who identified themselves as evening based chronotypes consistently performed better in the evening, regardless of the amount of sleep they had. This was true to a lesser extent for morning chronotypes, however this demonstrates that sleep, while important, is not the only factor related to cognitive performance. Therefore, the aim of this study is to measure the effect of sleep quality on cognitive performance and mood.
H0 there is no relationship between quality of sleep and subjective sleepiness, sustained attention or subjective mood. H1 there is a relationship between quality of sleep and subjective sleepiness, sustained attention or subjective mood. Method Participants In total a selection of 80 random participants’ results were used, all sourced from Monash University across all campuses. The age and gender of participants were not reported. All participants were aware of the aims of the study. Materials
Ksrolinska Sleepiness scale (KSS) – Measured subjective sleepiness of participants by participants allocating a number between 1 (very alert) 5 (neither alert not sleepy) and 9 (very sleepy) for both a good night’s sleep and a poor night’s sleep. The Positive and negative affect scale (PANAS) – Measured subjective mood by requesting participants to report how they felt at the time of the completing the test. This test had 20 items, 10 positive and 10 negative, each a different adjective describing how the participant felt.
Trial making task (TMT) – Measured sustained attention by testing participants on cognitive tasks, such as connecting encircled letters and number in order (e. g 1-A-2B) Digit symbol substitution (DSST) – Measured sustained attention by requiring the participant to convert non-related symbols into numbers in the shortest time possible. Stop watch SPSS version 15 for windows Design This study was a repeated measures design with an opportunistic sample that was two tailed with one factor, sleepiness, with two levels, good night’s sleep and a poor night’s sleep.
The independent variable was the quality of sleep and the dependent variables were subjective sleepiness (KSS), subjective mood (PANAS) and sustained attention (TMT and DSST). Procedure Firstly, all participants were required to read and sign a consent form if they wished to participate in the study. Once this was handed to the tutor, participants were free to complete the three tasks after both a poor night’s sleep and a good night’s sleep. Participants were given instructions on how to correctly carry out the tasks and instructed to complete these several days apart and in different orders, to counterbalance carryover effects.
Participants were then told to record and enter their results online before the 20th of April 2008. Once a participant believed they had had a good night’s sleep, they would complete the four measures (the KSS, PANAS, TMT and DSST) of sleepiness and mark the tests they performed accordingly (as either a poor night’s sleep or a good night’s sleep). Participants were instructed to complete the tests while still in their bed to counterbalance environmental effects.
Participants would then do the same for a poor night’s sleep and once the participant had collected all the data they submitted it online. Results The raw data were collected by participants entering their scores on each test online. The statistic that was used was a repeated samples t-test, done so to test the variance between each of the measures between a good night’s sleep and a poor night’s sleep. For the data analysis SPSS v. 15 was used and the level of significance needed to reject the null hypothesis was . 05.
The descriptive statistics table (below) contains the means for the measures of sleepiness, the number of participants, along with the standard deviation and standard error. It appears that participants reporting a poor night’s sleep demonstrated higher times and error rates on all measures of sleepiness, while participants reporting a good night’s sleep reported higher positive effects on the PANAS measure. A trend of subjective sleepiness reported less in participants when they recorded a good night’s sleep than when participants had a poor night’s sleep can be seen.
Other trends show sustained attention being reduced in participants reporting a poor night’s, as demonstrated by longer times. Participants when reporting a poor night’s sleep also had more errors on the TMT than participants reporting a good night’s sleep. Therefore, from only examining the descriptive statistics, it can be noted that participants reporting a good night’s sleep had better sustained attention, according to the measures used, than participants when reporting a poor night’s sleep.
The same can be said in regards to subjective mood, with participants when reporting a good night’s sleep having less negative affect words (than participants when reporting a poor night’s sleep and more positive affect than a poor night’s sleep. A t test was performed in order to determine the significance, if any, of the relationship between quality of sleep and subjective sleepiness, sustained attention or subjective mood. This table describes the t score, the degrees of freedom and the significance level.
The t statistic showed that there was a significant difference between the means of all the pairs that could not be explained by chance. Essentially, this means that the quality of sleep affects subjective sleepiness, sustained attention and subjective mood. The KSS t-test suggests that there was a significant (p<. 05) different between the KSS rating for a good night’s sleep and a poor night’s sleep, meaning participants who recorded a good night’s sleep means were significantly lower (more alert) than participants reporting a poor night’s sleep.
The TMT time and error tests both suggested that participants reporting a good night’s sleep had significantly faster times and less errors then participants reporting a poor night’s sleep. Similar results are concluded from the DSST, with participants reporting a poor nights sleep finishing the task with significantly slower times with more errors than participants reporting a good night’s sleep. Finally, participants reporting a good night’s sleep recorded significantly more positive adjectives and less negative adjectives on the PANAS than participants reporting a poor night’s sleep.
Discussion The aim of this experiment is to measure the effect of sleep quality on subjective sleepiness, sustained attention and subjective mood. This was done by using the KSS to measure subjective sleepiness, the TMT and the DSST to measure sustained attention and the PANAS to measure subjective mood. The null hypothesis was rejected and the alternative hypothesis was supported, that being there is a relationship between quality of sleep and subjective sleepiness, sustained attention or subjective mood. The results show that there is a significant (p <. 5) difference between all of the dependent variables to the independent variable. The results obtained in this experiment are consistent with results obtain from previous research. Taylor & McFatter (2002) determined that sleep deprivation ‘had an overall negative effect on…mental performance’. The results from this study demonstrated a significant (p <. 05) difference in the mental performances of participants who had reported a good night’s sleep and participants who had reported a poor night’s sleep.
In this way, the current research supports Taylor & McFatter’s finding, in that participants who report a poor night’s sleep had poorer results on the cognitive tests, the TMT and the DSST, than when participants reported a good night’s sleep. Kamdar, Kaplan, Kezirian & Dement (2004), reported similar findings, determining that sleep debt, resulting from lack of sleep, resulted in poorer cognitive functioning during the day, leading to a reduced state of alertness. Conversely, Ellenbogen (2005), found that healthy amounts of sleep were beneficial to cognitive functioning.
This was similar to results in the present study, with participants who reported having a good night’s sleep doing well on cognitive tasks. Results obtained by Oginska & Pokorski (2006) are quite similar to results in the present study in that they report findings of adverse effects from poor quality sleep on mood. Oginska & Pokorski found that 45% of participants experiencing fatigue due to an insufficient amount of sleep experienced irrational mood swings more frequently and also more irritability than participants who were well slept.
In the present study, mood, as measured by the PANAS, was found to be effected by quality of sleep, with participants who reported a good night’s sleep using significantly (p <. 05) less negative adjectives and more positive adjectives than participants who reported poor sleep. Similar results were also obtained by Touitou, Portaluppi, Smolensky & Resning (2004) who found poor sleep quality negatively effected alertness. They reported that 76% of participants who experienced poor sleep considered themselves less alert then when they had a good night’s sleep.
In the present study, the results are almost identical, with a significant (p;. 05) number of participants feeling less alert after a poor night’s sleep compared to a good night’s sleep. The results of the present study suggest that participants have better sustained attention, subjective mood and subjective sleepiness when they have received a ‘good’ night’s sleep. This means that there are several implications that can be taken from this study and extrapolated to the wider community.
Firstly, educational facilities are heavily affected by their students’ alertness, sustained attention and subjective mood. Using the results from this study, it would be suggested that educational facilities with strict timetables, like high schools, should begin the first class at a time that allows student sufficient time to sleep. This is suggested because if a student is allowed enough time to sleep, it will increase the sustained attention, useful for concentration at school, as well as mood and alertness in class.
Other implications are for road safety, whereby the governing road safety body, such as TAC or VicRoads, could use this information when considering how to increase road safety through raising awareness of the importance of being awake when driving. Furthermore, in the work force, increasing sleep quality and time for shift workers may be a priority where sustained attention may be important, for example a doctor. Using the present study as a guide, increasing sleep time could potentially increase performance and better the mood of the employee. Limitations of this study were that environmental factors may have affected the data.
As there was no formal data collection by an experimenter in controlled conditions, the data collection method could have been improved to increase validity. Environmental factors that may have contributed to inaccuracy were that the participants may not have stayed in bed while completing the tests. In addition, participants may not have completed the test within 30 minutes of awaking up. When the participants completed the tests could not be monitored and as such participants may have completed the tests too close together and carryover effects may be altered the data.
The main outcomes of this study were that a significant (p;. 05) relationship was found between quality of sleep and subjective sleepiness, sustained attention and subjective mood. It was found that the better quality of sleep is obtained, the less subjectively sleepy, higher sustained attention and more positive subjective mood the participant has. The present study was in line with several other studies undertaken, with many of the findings being reflected in both this study and others. Limitation such as environmental factors and carryover effects may have the data.
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