Does caffeine affect reaction time?

Introduction

Psychology and neuroscience have been interested in motivation and its relationship to addiction since early on, seeking to understand why an individual engages in a given behavior, even when it becomes compulsive and potentially harmful. Caffeine is one of these substances that can cause addiction. It is a psychoactive substance that works by inhibiting the action of adenosine, a neurotransmitter present throughout the body.

Although often associated with coffee, from which it takes its name, caffeine is also present in many products such as tea, chocolate, and plants such as kola nut, guarana, and mate. It is also found in many soft drinks (especially colas), as well as in certain medications, such as painkillers and flu treatments.

Caffeine has multiple effects on performance: it tends to reduce reaction time and improve individual performance, thus encouraging its consumption to maintain optimal alertness. It can therefore be perceived as a potential reward, likely to induce addiction in the medium term.

Terry Robinson and Kent Berridge developed a theory of addiction called Incentive Sensitization Theory of Addiction, according to which repeated exposure of the nervous system to an addictive drug, such as caffeine, can cause a motivational awareness – a change in motivational processes related to the search for and consumption of the substance. It is therefore relevant to understand whether caffeine actually improves performance by inducing a feeling of satisfaction.

Objective and assumptions

This experiment aims to observe whether caffeine influences reaction time.
The experimental hypothesis tested is that caffeine decreases reaction time. This is a directional hypothesis, because it establishes a causal link between two variables: caffeine consumption and reaction time.

• L'null hypothesis states that caffeine has no effect on reaction time.

• There independent variable is the amount of caffeine administered (identical for each participant).

• There dependent variable is the time taken to catch a ruler, measured in centimeters on the scale.

Methodology

A pilot project was conducted with two participants. They were asked to drink an espresso (average dose of 89 mg of caffeine), then catch a ruler falling vertically.

According to Health Canada (2003), a noticeable effect of caffeine appears from 60 mg, lasting several hours. Here are some useful guidelines:

Undesirable variables can influence the results: emotional state, fatigue, mental preparation, duration of the experiment, environmental conditions, etc. These variables were controlled by carrying out the experiment in the same place, at the same time (9 a.m.), when caffeine is considered more effective.

Selection of participants

Five colleagues were contacted via a preliminary questionnaire to:

• Check for medical contraindications (allergy, hypertension, anxiety, ulcers, insomnia, etc.).

• Assess their degree of caffeine dependence.

• Create a homogeneous group (age, gender, education level).

Two women of about forty years old, in good health, were detained.

Procedure

After signing the informed consent, the following protocol was applied:

1. A ruler is held vertically; the participant places their hand at zero level.

2. The researcher releases the rule after a random delay.

3. The distance traveled before being caught is noted.

4. Each participant repeats this test Before And 30 minutes later having drunk an espresso.

Results

The table shows a slight improvement in reaction times after caffeine ingestion. However, with such a small sample, the results are not statistically significant.

A larger sample would have allowed:

• to calculate a average and one standard deviation ;

• to determine a p-value (probability that the results are due to chance);

• to use a Student's t-test to compare the two data sets.

In this case, since the p-value is close to 1, the null hypothesis cannot be rejected. A larger sample size could allow a p-value of less than 0.05 – the conventional threshold for scientific significance.

Discussion

Previous studies suggest that caffeine reduces reaction time, but our sample is too small to draw general conclusions. The initial (more ambitious) methodology called for a study by sex, as well as a control group not exposed to caffeine – which could not be implemented due to a lack of participants.

The rule test, simple to administer, is relevant but sensitive to individual performance. Hence the need for a group of at least 20 people.

THE selection questionnaire has proven essential for both reasons ethics (safety of participants) and scientists (sample homogeneity). The caffeine dosage, although based on reliable sources, could have been validated by medical advice.

This protocol could be extended on a larger scale within the framework of a study on motivation and caffeine addiction. It could also include a subjective survey of the feeling of pleasure linked to improved performance after ingestion.

References

Health Canada. (2000). Caffeine in food. Retrieved from http://www.hc-sc.gc.ca/fn-an/securit/addit/caf/food-caf-aliments-eng.php

McCusker, R.R., Goldberger, BA, & Cone, E.J. (2003). Caffeine content of specialty coffees. Journal of Analytical Toxicology, 27(7), 520–522. Retrieved from http://www.ncbi.nlm.nih.gov/pubmed/14607010