Multitasking gets a bad rap. While the ability to juggle several things at once seems like an impressive use of brainpower, evidence suggests it's bad for productivity and memory, and for our mental energy reserves.

Wikipedia even calls it "an apparent human ability", because many argue multitasking isn't actually real, but merely a false belief we're performing numerous tasks simultaneously – when in fact we're inefficiently and inattentively switching between them one at a time.

"Multitasking is often a matter of perception or can even be thought of as an illusion," explains consumer behaviour researcher Shalena Srna from the University of Michigan.

But while multitasking might be a figment of our imagination, a new study by Srna and fellow researchers suggests the effects of the illusion are quite real – and can even boost our performance in cognitive tasks (so long as we're convinced we're multitasking at the time).

Research debunking the human ability to effectively multitask goes back to the 1960s, but Srna's focus was different. We already know that multitasking lowers our performance at tasks, but what about the perception that we're multitasking; how does that itself affect performance?

It might seem like a strange distinction, but as the researchers point out, multitasking is very much a matter of perception. If you're taking notes as somebody talks, is that a single activity, or is it an example of multitasking (actively listening and transcribing at the same time)?

"Existing research demonstrates that individuals' motive for investing effort and cognitive control increases with the difficulty of the task as well as with the expectation of task difficulty," the authors explain in their paper.

"Indeed, several findings support the notion that a more challenging task increases individuals' attention and ultimately leads to improvement in performance."

On that basis, if people think they're multitasking while they do something, they might actually do better, cognitively compensating for the difficulty of juggling (perceived) multiple tasks.

In contrast, somebody else who viewed the same activity as a simple, single task might devote less effort, attention, and cognitive resources – and in doing so, perform less well, even though the task was otherwise identical.

To investigate their hypothesis, the researchers ran dozens of trials involving more than 8,000 participants in total, in which people were asked to perform the same tasks, but were given subtly different instructions about whether it was a single task or multiple tasks.

In one of the tests, participants watched and transcribed an educational video; half of the group were instructed it was a single task, while the other half were told they were being tested on two tasks (learning and transcribing).

In a similar experiment, participants had to take notes during an online lecture, again being given differing instructions as to whether it amounted to a single task or multitasking (although that word was not used).

Across the various experiments, the results generally showed that those who believed they were multitasking did better in the tests, transcribing quicker and more accurately, taking higher quality notes, and scoring better on comprehension quizzes.

"We found that, holding the activity constant, the mere perception of multitasking improves performance and that heightened engagement is an important driver of this effect," the researchers explain.

One of the experiments ran the same kind of test while using eye-tracking technology to monitor participants' pupil dilation while working on the tasks, which is used as a proxy for measuring individuals' attentional and mental effort, and processing load.

While there are limitations with the accuracy of this technique (which the researchers acknowledge), as predicted, the team found the multitasking group exhibited larger average pupil dilation than the single-taskers, suggesting they were exerting more mental effort to stay engaged.

The findings don't mean multitasking is somehow superior to single-tasking – decades of research already show otherwise.

But they do seem to suggest that multitasking – as a motivating concept in our minds, at least – isn't the uniquely limiting factor we perceive it to be.

The findings are reported in Psychological Science.