Knowledge Base

Issues

• A variable does not appear in my results
• I get unrealistic values of path shape and direction
• A subject shows rotational behavior. However, when I look at the stats of Angular velocity or Turn Angle, the values are lower than for a subject which does not show rotation. Why?
• I get different results in two EthoVision XT versions
• I get different results when I analyze the same video twice
• I want to validate angle variables like Heading, Head direction, and Heading to Point, but the average value I calculate in Excel does not match the results in EthoVision XT
• The total distance moved does not always match the mean velocity
• I want to analyze Activity to detect freezing in rodents. However, when I plot the data I get lots of Inactive states
• I get wrong statistics of manually-scored behaviors
• The statistics result table contains many empty rows or columns
• The statistics result table contains two or more values of a dependent variable for the same trial, arena or subject
• The statistics result table does not appear
• The Data Preparation Report says "Failed" for some trials
• The percentage of "Subject not found" does not match the time in the arena
• The results table contains "?" in many cells
• How do I know the time between the starting point of a video and the time that I started tracking?
• I get more zone entries than expected
• The Analysis profile does not list Mobility and Head direction

A Variable Does Not Appear in My Results

One or more of the following may be the case:

• The experiment is not set to Nose-point, center-point and tail-base point tracking.
• You do not have the add-on module that allows to calculate those variables.
• For social behavior variables: double-click a variable in the Analysis Profile and define Receivers there.
• Your experiment is set to Live Mouse Tracker. This type of experiment does not contain the raw data needed to calculate variables like Mobility, Head direction and Body elongation.

See Also

• Dependent Variables in Detail: Social

I Get Unrealistic Values of Path Shape and Direction

Variables like Meander may have very high values (e.g. 5000 º/min) despite the fact that the animal moves approximately on a straight line. High values of the variable occur when body points for consecutive samples (that is, at times t-1, t, t+1...) lie near each other. For example, when the sample rate is high, and the subject does not move much, the distance moved between consecutive samples is very small, consequently Meander (which is by definition Turn angle divided by Distance moved) will be very high.

In this case it is useful to filter data using the Minimal Distance Moved method. To choose the threshold, plot the data of Distance moved together with your variable. For example, if you see that values of Distance moved around 0.05 produce unrealistic values of the variable, set Minimal Distance Moved = 0.1.

If this does not fix the problem, try re-tracking from the same video, but with a lower sample rate.

See Also

• Dependent Variables in Detail > Path
• The Minimal Distance Moved Smoothing Method

Angular Velocity Values Are Lower for a Rotating Subject Than a Non-Rotating Subject

Angular velocity does not necessarily correlate with rotations. If the animal turns slowly, its Angular velocity is low. Furthermore, when the subject sits still, but its body point oscillates in all directions due to random noise, high values of Turn angle (and therefore Angular velocity) will appear. To minimize this effect, either use the Minimal Distance Moved filter (see the previous issue), or nest over Movement to only select the data points when the animal is Moving. Then, calculate your variables. The figure below compares Angular velocity calculated for when the animal moves significantly, with when it does not move.

To quantify rotational behavior, also use Rotation.

I Get Different Results in Two EthoVision XT Versions

The possible causes of this issue are:

• You specified a sample rate that is lower than the maximum sample rate; in that case EthoVision XT analyzes every nth video frame (where n is the video frame rate divided by your sample rate; for example if you choose a sample rate of 12.5 for a video file of 25 frames per second, then n = 2, that is, the software analyzes every two frames). In some previous versions, EthoVision XT always took the second frame in the video and every nth frame thereafter. The results like distance moved may be slightly different, but that is very unlikely to affect the outcome of an experiment.
• EthoVision XT 17.5 and later play video using the GPU by default. In contrast, EthoVision XT 17.0 and earlier used the CPU. This may result in slight differences in the appearance of the video image, for example, video looking brighter, which in turn could affect detection and the tracking results. You have two options:
  • Revert to playback with the CPU in the Preferences for video settings.
  • Keep using the GPU and adjust the detection settings in the new version so they match the detection in the old version as much as possible.

Source: EthoVision XT 19 Help, Noldus Information Technology