In this new series, we explain step by step how visual behavior can be analyzed. The first installment introduces four fundamental eye-tracking metrics — fixations, saccades, smooth pursuits, and scanpaths — and shows how they significantly deepen the understanding of how users and professionals perceive visual information.
Fixations – Where Your Eyes Actually Capture Information
Humans move their eyes because the retina—the light-sensitive layer at the back of the eye—contains a small, high-resolution region called the fovea. When we notice something in our peripheral vision, we typically shift our gaze so that the object’s image falls onto this sharper area. This process is commonly described as “fixating”. Fixations are periods in which the retina is stabilized over a stationary object of interest , and they typically have a duration of between 200 and 300 milliseconds.
Eye tracking captures fixations by measuring their duration, frequency, and location, revealing accurately where people’s attention is actually directed. In practice, this can be used to:
- improve quality control in manufacturing,
- test whether call-to-action buttons on landing pages actually stand out,
- train pilots to better prioritize cockpit instruments, or
- optimize visual strategies in surgical procedures within healthcare.
It’s worth noting: long fixations don’t always signal interest—they can also indicate confusion or show that there is a lot of information available that needs to be perceived. Context is key.
Saccades – The Rapid Jumps Between Fixations
Saccades are the rapid eye movements that occur between two fixations, typically lasting just 30-80 milliseconds. During these movements, images sweep across the retina, yet we remain perceptually unaware of this motion.
Eye tracking captures and analyzes saccades by measuring their amplitude, velocity, and direction. This makes it possible to understand how someone searches for, navigates through, and processes visual information.
In practice, these patterns can reveal a great deal about performance and behavior. Given a specific task, irregular or erratic saccades may indicate stress, fatigue, or inexperience, as in the case of a driver, while short, targeted saccades often reflect a higher proficiency, during the inspection of an X-ray image, for example. In sports, elite athletes tend to exhibit efficient and accurate saccades, whereas beginners display less structured eye movements. Similarly, in cockpit design, analyzing saccade patterns helps optimize the placement of instruments for faster and safer operation.
Important to remember: fewer, well-targeted saccades generally reflect greater expertise. Together with fixations, they offer a comprehensive view of how we perceive and process visual information.
Smooth Pursuits – Following Objects in Motion
Smooth pursuits are continuous eye movements that allow us to follow moving objects, in contrast to the rapid saccades that occur between objects. During smooth pursuits, the eyes adjust their speed smoothly to match the movement of the target. This is essentially a fixation in which the object we are focusing on is not stationary but moving. For the image of the object to remain on the fovea, the eye must move accordingly.
Eye tracking primarily measures how accurately the eyes follow an object and how quickly they respond. This makes it possible to assess how effectively someone follows and processes moving stimuli. In practice, its impact is evident in sports, where elite athletes demonstrate remarkable precision when tracking balls or opponents, and in how viewers naturally follow moving elements in videos or advertisements. Insights are also valuable in cockpit environments, where pilots must track aircraft or instruments during dynamic situations, and in medical diagnostics, where impaired smooth pursuits can indicate neurological conditions.
An important point: the quality of smooth pursuits is a strong indicator of performance in dynamic environments. Modern algorithms can automatically distinguish between fixations, saccades, and smooth pursuits, ensuring reliable and detailed analysis of the data.
Scanpaths – Tracing the Route Your Eyes Take
A scanpaths represents the complete sequential path of eye movements across a scene, connecting fixations with saccades in chronological order. Scanpaths emphasize the overall strategy and pattern of visual exploration. Analysts measure features such as path length, direction changes, repeatability, and similarity between participants to gain insight into how people navigate a visual environment.
Scanpaths are particularly valuable for understanding navigation strategy, learning progression, and expertise levels. In manufacturing, experienced operators follow optimized, consistent scan paths during assembly, with deviations signaling training gaps. In aviation, pilots develop precise instrument scan paths, and breakdowns in these paths can indicate safety risks. Retailers study shopper scan paths across shelves to optimize product placement, while radiologists with systematic scan paths are less likely to miss anomalies compared with chaotic scanning patterns.
An important point: gaze plots help explain why a heatmap highlights certain areas, revealing the strategies behind those patterns.
Conclusion
With fixations, saccades, smooth pursuits, and scanpaths, four fundamental eye-tracking metrics have been introduced. Together, they form the foundation for systematically understanding visual behavior and for placing initial analyses into the right context.
This foundational knowledge makes it possible to interpret eye-tracking reports more effectively and to independently analyze basic questions—whether in UX design, training programs, or safety-critical applications.
The second part of this series focuses on advanced metrics that allow impact and efficiency to be quantified. These include Time to First Fixation (TTFF), Dwell Time, AOI analyses, and gaze Plots which play a key role in ROI-driven evaluations.
Don’t miss the second part of this series—along with other articles and practical examples on eye tracking, all published regularly in our newsletter.
