Knowledge Base

Detection Settings

General

Ensure your subjects are detected well by Ethovision XT. Choose Setup > Detection Settings. For more details, see the EthoVision XT Help.

Sample Rate

In the Video section, specify the sample rate. Some commonly-used values are:

• For tracking rats: 5 samples/second.
• For tracking mice: 12.5 samples/second.
• When tracking the nose- and tail-base points of rodents: 25–30 samples/second.

Detect Immobility

There are two ways to detect immobility of the subject during the trial.

• Activity measures the number of pixels that change their intensity, so whenever the subject sits still, the Activity value will be low. However, when the subject is connected to a microscope cable, the cable can move continuously and keep Activity high.
• Mobility is based on the change of the detected shape (i.e., the yellow blob). You can define Mobility in the Analysis profile, so you do not need to specify anything in the Detection Settings. However, make sure that the yellow blob covers the entire body of the subject and is not affected by the cable.

As a result of cable interference, Activity measurements may not detect immobility with sufficient accuracy. Instead, use Mobility.

Remove the Effect of the Microscope Cable

When the microscope cable is detected as the subject, it changes both the Mobility measure and the position of the center point. The latter affects distance moved and other readouts.

Step 1 – Define the Contrast

Make sure that the entire body of the subject is well detected throughout the arena. Use Dynamic Subtraction and choose the smallest range of contrast that enables detection of the subject's body. Ensure that the contour of the subject is not too much indented and that noise (i.e., the orange areas) is limited. Note that the cable may still be detected at this stage and will be removed in the next step.

Step 2 – Erode and Then Dilate the Contour

In the Detection Settings, locate the Subject Contour options. Select a value for the first Erosion and a similar value for Dilation until the cable is no longer highlighted in yellow.

• The Erosion filter removes pixels from the contour, including those representing the cable.
• The Dilation filter restores the original size of the yellow blob but excludes the cable.

Source: EthoVision XT 18 - Application Manual, Noldus Information Technology