Thursday, October 16, 2014

The Effects of Caffeine on Cognitive Fatigue

A study performed by Sunni Newton (2009) sought to examine the effect of caffeine on cognitive fatigue. This study examined the effects of caffeine on performance and self report mood measures during the execution of complex cognitive tasks. The end results of this study showed that complex task performance improved while using caffeine.

Cognitive fatigue is a factor that decreases task engagement and increases the resistance to further exert energy towards a task. Cognitive fatigue observed through changes in a person’s work performance, their physiological processes, and subjective feelings.  

To perform this study, Newton split 116 participants into two groups, a control group that was given a placebo and an experimental group that was administered a dose of caffeine. Participants received the caffeine dose (170mg) or the placebo by chewing two pieces of gum after the first hour of the test. The dose was given after an hour to ensure that a baseline was gathered for the experimental group.

Groups of 2 to 12 persons participated in a 4.5 hour testing session which alternated between self report questionnaires and exam questions. The questionnaire solicited responses from the participants regarding alertness and their perceived level of fatigue, while the exams were problems sets composed of 8 questions. Newton compiled the questions from college textbooks on the following subjects: science, history, English, and human interest.

The results of the study, which Newton analyzed using an ANOVA, showed that the placebo group reported a greater amount of fatigue throughout the test while the caffeine group reported less fatigue and performed better on the complex tasks.
Figure 1. Mean hourly test performance for caffeine and placebo conditions

This study was well constructed and executed. The choice to administer the caffeine dose an hour into the test was well thought out and further highlighted the effects of caffeine on task performance. An examination of the effects of caffeine on performance over a longer test time would be interesting to see.

Additionally, participants only had 6 minutes to complete each of the test questions. The constant changing of topic and requirement may have served as a stimulus to the placebo group. It would be beneficial to examine the performance on tasks that take a greater amount of time to complete


Newton, Sunni. (2009). The effects of caffeine on cognitive fatigue. Georgia Tech University.


  1. John,

    Does Newton provide an example of a complex task in the experiment? The researchers in the article I reviewed on the effects of stimulants during sleep-deprive tasks found that the subjects realized the most significant performance enhancing effects compared to the placebo group for tasks requiring speed and accuracy versus tasks requiring accuracy alone. Is this finding commensurate with Newton's findings?

  2. The tasks Newton assigned were exam type questions from college textbooks.

    Additionally, participants only had 6 minutes to complete each of the questions, thus incorporating the speed aspect you alluded to.

  3. This study is interesting, particularly because I would want to have no part of the testing group (4.5 hours!?). It's one thing to feel less tired or get more done, but it's another to do things correctly or accurately. Related to Ricardo's question, I'm guessing this research does not address accuracy at all?

  4. maggie.danhakl@healthline.comNovember 10, 2014 at 1:45 PM

    Hi John,

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  5. Interesting study on caffeine. I love to drink a cup of coffee in the morning. But not after that. I wish to take healthier beverages such as Goji Berry Juice.