Effects of caffeine on vigilance and cognition

Kilpelainen et al carried out research on the effect of caffeine on vigilance and cognitive performance during extended wakefulness in 2008¹. Results (see illustration 1) show differences in the vigilance test results of pilots who were in the caffeine and placebo group. Although the average number of correct hits to measure vigilance test varies each time it was assessed, the significance decrease in performance was seen on the second day with less correct hits. Generally, the caffeine group always hit more targets than the placebo group which could suggest that the overall caffeine group's vigilance is slightly better. This is especially noted in day two where the caffeine group performed better in vigilance test. The table also shows that vigilance was impaired when there was an increase in sleep deprivation (SD).

Illustration 1. Performance in cognitive tasks during extended wakefulness
		Sustained attention²		Reaction time³		Learning⁴
Day	Measure	Placebo	Caffeine	Placebo	Caffeine	Placebo	Caffeine
1	1	32	33	650	660	—	—
1	2	31	32	660	710	263	210
1	3	31	35	650	640	167	210
Average		31	33	650	670	215	210
2	4	22	32	780	680	—	—
2	5	21	27	840	710	163	143
2	6	18	24	900	840	160	127
Average		20	28	840	740	162	135

The research also measures the effects of extended wakefulness on mood by numerous subjective assessment. These are summarised in illustration 2. The summary points out that confusion in the placebo group and inefficiency in the caffeine group shows no change. Levels of fatigue, vigor, inefficiency and confusion which were used to measure mood increased in both groups except for the decreased level of vigor in placebo group.

In addition, some caffeine withdrawal symptoms were subjectively assessed. The results ( see illustration 3) show that caffeine withdrawal symptoms/ill effects increased significantly during the long sleep deprivation time. However, the placebo's group well being and blurred vision were not significant.

Methods

Research approach

This research was an exploratory research to find out the effect of caffeine on vigilance and cognitive performance during sleep deprivation. This include sustained attention, learning tasks, and subjective rating on sleepiness, mood and motivation.

Sample

A convenience sample of 15 Finnish military student pilots were randomly assigned. There were a total of three sessions, five student pilots participating in each session. The control group has eight pilots and the experimental group has seven pilots. Their average age was 23 to 24 years.

These participants were habitual consumers of caffeine in forms of tea or coffee. This was crucial because participants who were not habitual users of caffeine products could have experienced higher effects from the caffeine, even small amounts of caffeine product consumption.

Variable

Independent Variable (IV). IV is the caffeine. The experimental group received 200 mg of caffeine and the control group received the placebo.

Dependent variable(DV). DV is the vigilance and cognitive performance. Vigilance was measured using sustained attention task and different subjective assessments were used to measure cognitive performance.

Materials

A placebo and 200mg of caffeine were used to measure the vigilance and cognitive skills.

Vigilance was assessed using the Mackworth clock test taken from Teikari (1977) which was run in a computerised environment.

Sleep dairy were used to keep record of participant's sleeping records 4 days prior to experiment.

Hiragana and spoken syllabus were used to asses learning tasks. Consonic CD-610M earphone were used to listen the syllabus.

As part of subjective assessments, subjective sleepiness was evaluated by using the Standard Sleepiness Scale. Participants were asked to choose a scale rating ranging from 1 ( feeling active and vital; alert; wide awake to 7 (Almost in reverie; sleep onset soon; loosing the struggle to remain awake).

Mood was measured using the Profile of Mood States Questionnaire using 32 different questions to describe subjective feelings of each of the questions rated from 0 (not at all) to 4 (extremely). Additionally, five subjectively assessed caffeine withdrawal symptoms/ill effects questionnaire were used.

To measure motivation and perceived performance, a 10cm visual analogue scale were used. Four questions was used and each had answer options of 'not at all' and 'very much'.

Procedure

All 15 pilots were randomly selected in double-blind fashion so they received either the placebo (n=8) or caffeine in a capsule (n=7) one hour before each of the four simulator flights. Additionally, all participants received the placebo before the first simulator. This was done in order to determine a baseline level and also to measure if there was any differences between the groups. Participants were told not to take any caffeine products during the 12 hours preceding the test procedure.

The simulator for sustained attention task was carried out four times. The vigilance test was done six times and the learning task was carried out three times. For the attention task student pilots were required to pay attention on the screen and respond as quickly as possible to the target. As part of the learning task, student pilots had to learn the association between hiragana symbols and spoken syllabus.

Data analysis

SPSS 14 was used to carry out data analysis. Repeated measure analysis of variance ( ANOVA), Mann- Whitney U-Test, Friedman's two- way ANOVA, Wilcoxon signed- rank test were applied.

Generalization potential

Limited generalisation. The generalisation can only be applied to a group of 24 year old military student pilots who are habitual caffeine drinkers. Apart from these results there appears to be little relevance to other populations and age groups.

References

1. KILPELAINEN Airi A, Kerttu H HUTTUNEN, Jouni J LOHI & Heikki LYYTINEN (2008). Effect of caffeine on vigilance and cognitive performance during extended wakefulness. International Journal of Aviation Psychology, 2010, volume 20, number 2, pages 144-159.

+++ Footnotes +++

2. Correct hits in the sustained attention task. The actual number of hits were not provided in the original article, so they have been estimated by 'eye-balling' the available figure. Consider them approximations only.

3. Reaction time in milliseconds in the sustained attention task. The actual milliseconds were not provided in the original article, so they have been estimated by 'eye-balling' the available figure. Consider them approximations only.

4. Learning trials required to learn the association of a verbal syllable with a pictorial character. The actual number of trials were not provided in the original article, so they have been estimated by 'eye-balling' the available figure. Consider them mere approximations.

Want to know more?

Subjective measure of the effect of the caffeine : This pages summarise the data in subjective measures of the effect of caffeine

Caffeine in aviation : This pages briefly tells us role of caffeine in human body, effect of high dose and performances of pilot and ATC.

Cognitive performance : This pages tell us about improving cognitive performance.

Perception of energy drinks (caffeine) among student pilots. :The article provides perceived physical, psychological and practical effects of energy drinks amongst student pilots.

Original article : Full original article of this research can be obtained from here.