Surprising limits of human imagination revealed by science

Have you ever tried tossing a handful of balls in the air and keeping track of each one at once? No matter how hard you focus, at least one will slip from your mind.

Researchers say this challenge reveals the surprising limits of human imagination, as a recent study shows we can only follow two moving objects at the same time.

The team drew inspiration from a process that enables tracking multiple moving objects simultaneously, known as the Multiple Object Tracking (MOT) paradigm. 

How far can human imagination go?

Researchers took the concept of “mental simulation” to design a new study, despite knowing that we do not always engage in simulation. And if we do, there are limitations to it.

They wanted to test whether people could imagine the future path of more than one moving object at a time, or whether we are limited to just one.

Previous studies on mental imagery have already shown that the more objects we add to our “mental screen,” the harder it becomes. It will also impair our precision in making judgments.

Searching for answers with IOT

But still, this study does not answer the question: how many such objects can be imagined at once? To answer this, scientists developed an experiment called the Imagined Objects Tracking (IOT) task.

Participants were asked first to watch animated scenes where objects moved across the screen until paused. Then they were told to imagine the movement of these objects and judge the timing of different outcomes.

Interestingly, the researchers focused on timing rather than the location of the objects.

They then compared the performance of the participants with two computational models that reflect different ideas on how the brain simulates moving objects.

Do we imagine one or many?

The first was a parallel model, which assumes people can track multiple moving objects at the same time. The second was a serial model, which assumes that people track just one object at a time.

After simulating one, they will switch to the next object. It predicts that when more objects are added, imagination slows down. 

Scientists noted the possibility of different subtypes of the serial model. For example, people might imagine the movement of one object for several steps, then switch to another, alternating back and forth.

At first, this seemed more reasonable, but it still did not fit all the data.

Then they thought of an approach that mixes both serial and parallel models, an interleaved model. But its predictions did not match either of the approaches, and were completely different from what the participants did. 

Unexpected results

When scientists tested the participants’ actual performance with their models, the result was surprising. Neither the serial, parallel, nor interleaved models provided a thorough explanation of what was happening. 

Instead, they found that people could only follow about two moving objects simultaneously in their imagination. This points to the bottleneck in mental simulation.

“We set out to test the capacity limits of the imagination, and we found that it was one,” said co-author Tomer D. Ullman, associate professor in the Department of Psychology at Harvard University.

Unlike our eyes, which can visually track multiple objects at once, our imagination seems to hit a hard limit. When forced to imagine numerous objects in motion, the brain struggles, affecting the accuracy.

So why does our imagination struggle to keep up? Prior research offers some clues.

How the brain tracks unseen objects

We often make vague calculations to track multiple objects in motion when they are in front of our eyes. But what if the objects are no longer visible?

In that case, we imagine them continuing to move in our head. Tracking an object does not simply stop when it crosses out of sight. The real question was, what is the actual limit?

Scientists still debate the mechanism by which the brain tracks unseen objects. Evidence from the MOT paradigm suggests that we do not always imagine the exact trajectories or paths of moving objects. 

Instead, we might rely on heuristics, meaning quick mental shortcuts or assumptions. For example, we might assume that an unseen ball rolling across a table continues in a straight line at a constant speed.

Others propose that some of us use “mental simulation”, where we track the path of the moving object step by step in our imagination. This approach has been helpful to explain how people think about the dynamics of moving objects.

Real-world impact of human imagination

The researchers concluded that our ability to simulate moving objects is limited. This suggests that human imagination works best when handling one or two dynamic elements at a time. 

This has implications for understanding not only visual imagination but also how people plan, predict, and make decisions in dynamic environments.

In other words, human imagination eventually lets some slip, reminding us that even our mental stage has boundaries.

The full study was published in the journal Nature Communications.

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