Knowledge Base

Frequently Asked Questions About Activity

1. What is the difference between Activity and Mobility?

   Activity is the percentage change in all pixels in the arena between the current sample and the previous sample. This is independent of the detected subject.

   Mobility is the percentage pixel change between the current sample and the previous sample in the detected subject only. See Rotation.

2. When should I use Activity and when should I use Mobility?

   Use Activity when the dependent variable Mobility does not give satisfying results, or if detection of your subject is difficult. This can be the case when bars of the shock grid floor in the background complicate detection of the animal's surface area, or when the animal is very large compared to the arena size.

3. Does Activity detection depend on the size of the subject relative to the arena?

   Yes. Activity is calculated as the number of changed pixels divided by the total number of pixels in the arena. The smaller the subject relative to the arena, the smaller the activity will be. When your animal is very large in comparison to the arena size, for example when you have a rat in a small cage, activity detection is generally more suitable than mobility detection.

4. Does Activity detection depend on the video resolution?

   Yes. The higher the video resolution, the greater the number of pixels that change when the subject moves. Therefore, when you have a high video resolution, it is less likely that a small movement of the subject results in an abrupt change in activity.

   However, this effect is present at very low resolution (for example, when the subject is less than 100 pixels large). We advise you not to compare values of Activity between videos of different resolutions.

5. Does Activity detection depend on sample rate?

   Yes. Since Activity is detected from the change in pixels between two samples, and the pixel change depends on how frequently the area is acquired (that is, the sample rate), Activity depends on the sample rate. All being equal, the higher the sample rate, the smaller the pixel change. See also the effect of the sample rate on Mobility in Frequently Asked Questions About Mobility.

Applications

Activity can be used to determine freezing behavior in rodents. Also, it may be used to assess inactivity of rodents in a Porsolt Swim Test. Furthermore, the startle response of zebrafish larvae can automatically be detected with (in)activity.

Definition

Body elongation measures how much the subject's detected shape differs from a circle.

NOTE Body elongation is not available if your experiment is set to:

• Center-point detection.
• Color marker tracking.
• Live Mouse Tracker (but see Stretch Attend Posture).
• Center-point, nose-point and tail-base detection, with two subjects per arena tracked with Deep learning.

Calculation

1. The Body elongation measure E is calculated as follows:

   • x, y are the coordinates of the pixels of the subject's contour in the current sample.
   • xc and yc are the coordinates of the center of the subject.

2. The Body elongation value is smoothed at each sample using the optional Averaging interval.

Body elongation is expressed as a percentage and ranges from 0% (when the subject's shape is perfectly circular) to 100% (when the subject's shape is a line).

How to Specify Body Elongation

1. Click the Add button next to Body elongation and click the Body Elongation tab.
2. Enter the Averaging interval. This is the number of samples over which the running average elongation is based. The default value is 1, that is, the variable is not smoothed using the values of neighboring samples. See Averaging Interval.
3. Complete the procedure to add the variable. See Calculate Statistics: Procedure.

Notes

• Body elongation is not calculated with Live Mouse Tracker data.

Source: EthoVision XT 19 Help, Noldus Information Technology