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A new study published in the Psychological Bulletin looked at a meta-analytic review of the association between mental effort and negative affect.

“In psychology, there is a decades-long controversy about the nature of mental effort,” study author Erik Bijleveld told us. “On the one hand, psychologists often assume that people avoid mental effort whenever they can.” 

Bijleveld cites an example of this when people make daily-life decisions such as what restaurant to go to, they are usually not going to process all relevant information that is available to them. 

“People often just go with their gut feeling,” Bijleveld told us. “This is one way in which people conserve mental effort, and there is a lot of research that supports the idea that people do often use these simple ways of making decisions. So, as people seem to avoid mental effort all the time, you can also reasonably assume that people dislike mental effort.”

On the other hand, Bijleveld explains, it is also very plausible that people can readily learn associations between mental effort and rewards. 

“For example, in schools and universities, students are often complimented after they have exerted mental effort,” Bijleveld told us. “Also, many religions suggest that effortful work is a good, pure activity. So, in life, there are plenty opportunities to learn that mental effort is linked to reward. Effort may be pleasant after all.”

The research team compiled a lot of previous data on humans who did a mentally effortful task, and meta-analyzed that. They asked whether mental effort feel unpleasant. if so, if it varies between tasks and between populations.

The researchers focused on all studies that used one particular self-report instrument, an instrument that was developed at NASA in the 1980s, the NASA-TLX (TLX stands for Task Load Index). This questionnaire includes items about effort (“how hard did you have to work to accomplish your level of performance?”) and negative affect (“how insecure, discouraged, irritated, stressed, and annoyed did you feel during the task?"). 

“This instrument has become a very popular standard instrument in ergonomics and psychology,” Bijleveld told us. “This way, we were able to include a wide range of studies with different populations and different tasks. In my view, the key strength of our study is the diversity of studies that we could analyze. We know now that mental effort is unpleasant across a very wide range of tasks and populations.”

The results of the study showed that across the board, mental effort was strongly associated with negative feelings, like annoyance, frustration, and irritation. Specifically, with each unit increase in mental effort, negative feelings increased with about 0.85 unit.

“I was not so surprised that there was generally an association between mental effort and negative feelings,” Bijleveld told us. “However, I was very surprised that this association was so robust.” 

Bijleveld explains that for example, one might expect that university-educated people have been extensively rewarded for mental effort in their past. While it would have made sense if mental effort would have felt less unpleasant for them, the researchers found no evidence for this at all. Also, you might expect that some tasks are just more fun and motivating than others. But even for tasks that had motivating ingredients, like performance feedback, more mental effort was associated with more negative feelings.

“One take home message is that unpleasant feelings during mental work, like irritation and frustration, are perfectly normal and extremely common,” Bijleveld told us. "So, if you are doing mental work and experiencing these feelings, this does not mean that you're unfit or incompetent or anything like that: negative feelings are a totally natural feature of mental work.”

The researchers realize that the results raise a lot of questions, such as: If effort is unpleasant, why do people choose mentally demanding occupations? Why do people play puzzles, like wordle and sudoku? Their interpretation is that all these activities come with rewards. 

“For example, when finishing a sudoku or a wordle, people may experience like they have accomplished something, which feels good,” Bijleveld told us. “Also, they may feel that their skills are improving, which is pleasant too. In our interpretation, these rewards can compensate for the mental effort – so, people still choose these activities, and self-report that they like them. However, we think that these rewards do not make the mental effort less unpleasant. So, people choose these activities and occupations despite the mental effort, not because of it.”