There is an extreme variety of metrics used in the practical application of eye tracking. Below, we examine the most commonly used ones.

Certainly the most important metrics for eye tracking. Gaze points constitute the basic unit of measurement: one gaze point is equivalent to a raw sample recorded by the tracker.

A heatmap is an overlaid visualization of the fixations that have occurred over time on a specific stimulus. They are generally displayed as an overlay of different color gradients on the image or the presented stimulus. The colors red, yellow, and green represent, in descending order, the quantity of fixations directed toward the various parts of the image.

If a gaze point is maintained for a certain amount of time, it becomes a fixation, a period during which the test subject’s eyes are locked onto a specific object.

Within a visual stimulus, it is possible to select one or more different regions (the AOIs) on which to concentrate the analysis, or to differentiate the metrics to be recorded in each. Although not strictly a metric itself, it defines the area based on which other metrics are calculated.

By specifying the order and direction in which fixations occur, it is possible to see what first captured a test subject’s attention and the manner in which the stimulus was viewed.

This indicates the amount of time it takes a test subject (or all respondents, on average) to look at a specific AOI from the onset of the stimulus.
Similar to fixation sequences, the time between the start of the stimulus and the viewing of a defined region provides information on when a particular AOI is seen for the first time. This information can be valuable for evaluating what is expected (and what is not) within a scene.