The heatmap color scale

Aim

To help estimate how much time the subject spent in a region of the arena.

Because heatmaps create gradients by definition, they are not meant to accurately measure the time that the subject spent in a certain zone. For that, calculate the statistics for the variable In zone. See Analysis advisor

To access this option

Choose Analysis > Results > Plot Heatmaps.

Locate the scale at the right-hand side of the heatmap.

Scale maximum

You find the maximum value at the top of the scale. It is expressed in:

▪Seconds, if you choose Cumulated as a Merging method for heatmaps.

▪A fraction of the track duration, if you choose Mean as a Merging method for heatmaps (see also a note below).

To calculate the maximum, EthoVision XT finds the pixel of the heatmap with the highest number of recorded positions and calculates the total time spent in a circular area around that position. The circular area depends on the Color smoothing that is currently set. The larger the smoothing value, the larger the circular are around the maximum, the higher the value in the scale because more point locations around the “peak” pixel are included in the calculation.

This correction is made because the highest absolute density of sample points (shown in dark red by default) is usually found in one or few pixels per track; taking only the cumulated time for those pixels would do not provide a realistic estimate of the time spent by a subject in a certain location.

Scale minimum

You find the minimum value at the bottom of the scale. This is always zero seconds (or fraction of the track duration; see above for Maximum). It represents the locations where the subject was never found.

Notes

▪The scale is plotted independently for each heatmap. The Maximum value only depends on the original data points that form that heatmap.

▪In order to make a good judgment when comparing heatmaps, make sure that the total track duration is the same or very similar between groups or subjects.

▪If you choose Over heatmap as Color level, the scale maximum also changes. For example, the maximum for that heatmap is represented with blue or green, not red. That happens because the overall maximum is found in other heatmaps. See Heatmap colors

▪If you choose Mean instead of Cumulated as a Merging method for heatmaps, the maximum is expressed as a fraction of the total time that the subject was in that region. If the subject keeps moving across the arena, this value can be rather low, for example 0.01. It means that the region of peak occurrence contained 1% of the positions.