Study finds caffeine increases task persistence under pressure

A new study provides evidence that caffeine can increase how long people persist in trying to complete difficult or unsolvable tasks, and this effect is especially pronounced in people who have recently experienced stress. The findings, published in Human Psychopharmacology: Clinical and Experimental, suggest that caffeine may promote a more active coping style in humans, in line with earlier behavioral findings from rodent research.

Caffeine is one of the most widely consumed psychoactive substances in the world, known for its stimulating effects on alertness and attention. In animal studies, caffeine has been shown to reduce what researchers describe as “immobility” during behavioral despair tasks like the forced swim test, which has traditionally been used to screen for antidepressant activity. However, more recent work has challenged the idea that immobility in these tests necessarily reflects despair. Some researchers now believe that reduced immobility may instead represent greater persistence or active coping in the face of difficulty.

This rethinking has raised questions about what decreased immobility really measures, and whether caffeine’s effects in animal models might translate to human behaviors like persistence during frustrating or impossible challenges. To test this possibility, the authors designed a set of experiments aimed at measuring task persistence in people, with and without caffeine, and in both stressful and non-stressful contexts.

“I originally got interested in caffeine research a number of years ago upon realizing that there was a dearth of research on the effects of caffeine during adolescence accompanied by an increase in consumption due to the introduction of energy drinks,” said study author Sarah M. Turgeon, the James E. Ostendarp Professor of Psychology at Amherst College.

The study was conducted in three experiments using 329 college students from Amherst College. The researchers used tasks specifically designed to include unsolvable components, allowing them to measure how long participants would continue trying after the solvable portion was complete.

In the first experiment, participants were randomly assigned to receive either no gum, a placebo gum with no caffeine, or a gum containing 40 milligrams of caffeine. After chewing for five minutes, they completed two tasks: a hidden picture task, where they had to find objects in a complex image (with one object intentionally missing), and an anagram task that included one unsolvable word. Persistence was measured by the time participants spent searching after all solvable items had been found.

The results of this first experiment showed no significant effects of the 40-milligram caffeine dose on either performance or persistence. Most participants solved the solvable portions of the tasks, and caffeine did not seem to increase the time they spent continuing to try.

The second experiment increased the caffeine dose to 100 milligrams, roughly the amount found in a strong cup of coffee. A new group of participants completed either the hidden picture task or a word search task, again with a missing item.

This time, participants who received 100 milligrams of caffeine spent significantly more time persisting in the hidden picture task. On average, caffeine increased the percentage of total task time devoted to searching for the unfindable item from 38 percent to 52 percent. However, caffeine did not influence persistence in the word search task, possibly due to differences in task structure or difficulty.

In the third experiment, the researchers explored how stress might interact with caffeine’s effects. They used the socially evaluated cold pressor test, a standard method for inducing mild psychological stress, in which participants are asked to hold their hand in ice-cold water while being observed. This procedure tends to raise cortisol levels, particularly 20 to 30 minutes after the stressor.

After undergoing either the cold water stress test or a warm water control, participants chewed gum containing either 0 or 100 milligrams of caffeine and completed the hidden picture task. The researchers found that stress improved task performance, with stressed participants identifying the seven solvable objects more quickly than their unstressed peers.

There was also a notable interaction between stress and caffeine on persistence. Among stressed participants, those who received caffeine persisted longer and spent a greater portion of their time searching for the unfindable object compared to stressed participants who received no caffeine. In contrast, among participants who had not experienced stress, caffeine appeared to slightly reduce persistence.

“Caffeine seems to have some positive effects on task persistence and these effects are influenced by stress,” Turgeon told PsyPost.

While the findings support the idea that caffeine can increase persistence in certain contexts, the researchers acknowledge some limitations. One issue is that participants who reached the task’s time limit had to be excluded from persistence analyses, which may have affected the results. Future studies could attempt to separate the measurement of performance and persistence more cleanly, perhaps by designing tasks in which these components can be independently assessed.

Another limitation is the lack of information on participants’ prior caffeine consumption habits in some of the experiments. While participants were asked to avoid caffeine for several hours beforehand, baseline tolerance levels were not strictly controlled, which could influence how they responded to the caffeine gum.

The researchers also note that persistence is a complex behavior influenced by many psychological and physiological processes. Caffeine may influence persistence by reducing fatigue, altering effort-reward calculations, or affecting neurotransmitter systems such as dopamine, norepinephrine, and adenosine. The role of stress hormones like cortisol also remains an open question. Future work may benefit from incorporating physiological measures or brain imaging to better understand the mechanisms involved.

In addition, while the study focused on a specific form of persistence — continuing to work on an unsolvable visual or verbal task — it is not yet clear whether caffeine would influence other types of goal-directed persistence, such as sticking with long-term projects or resisting distraction over extended periods.

“We are working to better design tasks to deal with these limitations and confirm our findings,” Turgeon said.

The study, “Effects of Caffeine and Stress on Persistence and Performance in an Unsolvable Visual Search Task in Humans,” was authored by Parssa Akbari, Sabrina R. Comess, Olivia Henkoff, Phyllis Oduor, and Sarah M. Turgeon.