Eye-tracking = mental fatigue detection

Can we measure mental fatigue?

In the first newsletter of this month’s focus on mental fatigue, I covered the causes, effects, and some of the methods we can use to detect mental fatigue.

To my own surprise, the review article I based that issue on highlighted eye tracking as the most reliable and practical method for detecting mental fatigue.

Naturally, I had to look into it. For me, the idea that eye tracking could be used to passively track mental fatigue is huge.

Just imagine—a small program running in the background on your computer (which we’re all staring at most of the day anyway), alerting you when signs of fatigue start building up.

That way, we could take a short break - just 5 minutes, as we've seen is enough in earlier newsletters - and return with renewed focus.

Today’s insights is mainly drawn from the scientific article: 

“A Review of the Use of Gaze and Pupil Metrics to Assess mental Workload in Gamified and Simulated Sensorimotor Tasks”

Today's newsletter

• Takeaways:

• The study in a nutshell:

• What they did:

• What the authors found out:

• What can we learn from this study?

• Quick Answers to Your Top of Mind Questions

Takeaways:

👀 Objective insight into mental state

Eye-tracking metrics could provide a real-time, objective measure of a persons mental state. The metrics are influenced my other factors, but if used correctly, it could provide insight into ones mental energy.

The study in a nutshell:

In this review, the authors looked at how eye-tracking and pupil measurement technologies could be used to track mental fatigue and cognitive workload.

The focus was on mental fatigue development in gamified or simulated motor tasks. These are game-like activities that involve physical movements used in rehabilitation.

The authors found that pupil dilation consistently increases with mental effort, making it a reliable indicator of cognitive fatigue.

Other eye behaviors like saccade speed, (quickness of eye movements that shift your gaze from one point to another) fixation patterns, and blink rate, can also reveal signs of fatigue, but are more sensitive to the type of task and to how the task is experienced.

These findings show that tracking eye movement could an objective way to monitor mental fatigue.

I find this technique extremely interesting, and have already spend quite a bit of time imagining how this could be used to optimize my own workday.

So, let’s dive in. 

What they did:

Today’s article is a systematic review, and included scientific studies that were published from 2000 to 2023.

To be included, studies had to use gaze- or pupil-based metrics to assess mental workload during gamified or simulated motor tasks.

In total, 15 primary studies and 4 reviews met these criteria, covering both healthy and clinical populations.

What the authors found out:

Saccades

Saccades are rapid eye movements that shift our focus from one spot to another - essentially it’s how the brain “scans” a scene.

The findings showed that slower saccades can indicate mental fatigue, while faster saccades may reflect higher engagement, motivation, or arousal.

The direction of change depends on whether the task is mentally stimulating or exhausting.

For example, a challenging task that feels rewarding may increase saccade speed, likely driven by heightened focus and dopamine-related arousal. In contrast, long or draining tasks tend to cause a drop in saccade velocity, reflecting growing fatigue or disengagement.

This decrease is thought to stem from central fatigue, where reduced output from the motor cortex - possibly due to neurotransmitter imbalances - leads to lower oculomotor drive and slower eye movements.
(If you have the time, you can gain a better understanding of this phenomenon here)

So, this sounds very promising.

But what if a task is interesting and slowly building mental fatigue?

We must assume that even interesting and rewarding tasks build mental fatigue (at least I know they can). To apply this technique in our everyday work life, we’d want it to signal when mental fatigue is starting to build up - even from meaningful or engaging tasks.

So, this metric properly can’t be used in isolation.

Fixation

Fixations are the moments when your eyes are not moving.

Today’s review found that the length at which people fixate can reflect different types of mental demand. For example:

• In cognitively demanding tasks (like solving a puzzle or making decisions), people tend to fixate longer but less frequently.

• In visually complex tasks (like fast-paced games with lots of visual input), fixations become shorter and more frequent.

The key insight is that fixation patterns help distinguish between mental fatigue due to cognitive load vs. perceptual overload.

So again, using this eye-metric alone might not be a strong indicator of mental fatigue, as many real-world tasks blend both types of demand.

Blink

Blinking happens both automatically and intentionally, and it turns out to be more than just eye protection - it also signals what's happening in your brain.

The review shows that blink rate tends to decrease during tasks requiring high visual attention, like tracking fast-moving objects or reacting quickly to stimuli.

But in tasks that involve internal mental processes, such as remembering information or planning a strategy, blink rate often increases.

So, this might give some useful insight into the development of mental fatigue.

However, its important to note, that blinking also is linked to dopamine activity. Therefore, it might also reflect motivation and reward processing.

For example, more frequent blinking has been observed when people are engaged in goal-directed tasks that feel meaningful or rewarding.

So, a low blink rate may point to intense visual focus, while a rising blink rate might indicate increased cognitive strain. But once again context is properly important, as blink rate might also increase as a result of increased motivation.

Pupil size

The authors highlight, that pupil size changes with mental effort and emotional arousal.

Across all the studies reviewed, pupil dilation emerged as the most reliable marker of cognitive workload.

When tasks become more challenging or demand more focus, the pupil typically widens. This response happens within milliseconds and can reflect subtle shifts in mental strain.

But again, one needs context to really know what’s going on.

Pupil size doesn’t tell you why arousal is increasing. It reacts to both positive stress (like being challenged and engaged) and negative overload (like feeling overwhelmed).

In some tasks, pupil size followed an inverted U-shaped pattern—increasing with task difficulty up to a point, then dropping off when the task became too hard or demotivating.

Because it reacts so quickly and consistently, pupil dilation could be a robust, real-time indicator of mental fatigue. However, it needs to be combined with contextual information or additional metrics in order to interpret the changes correctly.

What can we learn from this study?

Today’s review article really shows that tracking our eyes is a way to gain insights into our mental state.

Among all the metrics, pupil dilation seemed to be the most consistent and sensitive indicator of mental workload, potentially making it a valuable tool for detecting early signs of cognitive fatigue. Saccade velocity, fixation patterns, and blink rate offer additional layers of insight.

However, all these metrics are also influenced by factors that are more context dependent, like motivation, task difficulty and the type of visual stimuli.

So, I believe the real potential is in combining some of these metrics – possibly also with other measurements – to create an algorithm that can be used to track mental fatigue.

I’m personally very intrigued be this science, as I believe these insights offer a powerful tool for self-optimization.

Imagine using simple eye-tracking data to measure your mental alertness throughout the day.

Instead of relying your subjective feelings of alertness or your boss’s satisfaction with your work, , you can objectively measure when your brain is working too hard - or not hard enough.

This opens the door to personalized strategies, like adjusting task complexity, scheduling regular breaks, or even optimizing your work environment to maintain peak focus.

This is extremely interesting and potentially very useful for young ambitious professionals like us. Its something I will continue to look into.

Quick Answers to Your Top of Mind Questions

🙋‍♀️   How can eye-tracking technology benefit my workday as an ambitous professional?

By using eye-tracking to monitor important metrics you could potentially have a way to objectively gauge your cognitive workload and mental fatigue. This real-time insight allows you to adjust your work pace, schedule breaks, and modify your tasks to maintain peak focus and productivity.

_{Disclaimer: The above is mainly based on the article “A Review of the Use of Gaze and Pupil Metrics to Assess Mental Workload in Gamified and Simulated Sensorimotor Tasks” by Holly Gorin, Jigna Patel, Qinyin Qiu, Alma Merians, Sergei Adamovich & Gerard Fluet and aims to provide key takeaways and a condensed overview of its content. While the essence is drawn from the original article, some parts have been simplified or rephrased to enhance understanding. Please note that we at, OptiMindInsights or any other potential writers or contributors to our summaries, do not accept responsibility for any consequences arising from the use of this summary. The information provided should not be considered a substitute for personal research or professional advice. Readers are encouraged to consult the original article for detailed insights and references. The summary does not include references, but they can typically be found within the original publication. Always exercise due diligence and consider your unique circumstances before applying any information in your personal or professional life. We refer to the creative commons for reproducibility rights.}