# Subjects per arena

Aim

To specify the number of subjects that are present in each arena during a trial. This setting is valid throughout the experiment, and cannot be changed after you have acquired the first trial.

Procedure

1.Choose Setup > Experiment Settings.

2.Next to Number of Subjects per Arena, select the number of subjects that are present in each arena simultaneously.

If you intend to use the Deep learning technique for body point detection, you can apply it to one or two subjects per arena. See Body point detection technique

3.Under Subject roles, enter the role of the subjects or accept the default ones (Subject 1, Subject 2, etc.).

Subject roles

To modify the Subject's role name, right-click a name, select Rename and type in the new name. Enter generic role names, for instance in a Resident-intruder test with two animals, enter Resident and Intruder, or Mutant and Wild type.

Do not enter the ID of the subjects you are going to test. You can specify the ID of your subjects as an independent variable. See Define an independent variable

If you use the Deep learning technique to track two subjects in an arena, the software does not know which role belongs to a specific individual. So it may happen that the resident subject is labeled Resident in one trial, and Intruder in another trial. To correct this, open the Track Editor and swap the subjects in the trial where the resident subject is labeled as Intruder. See Swap subjects

Notes

▪With the Base version of EthoVision XT you can track one subject per arena.

▪With the Social Interaction Module, you can track up to 16 subjects per arena. Mind that this is a technical limit; the actual number of subjects that you can track depends on other factors. When using color markers to discriminate between individuals, it may be difficult to discriminate between 16 different color marks depending on the light conditions.

▪To change the number of subjects per arena after acquisition, either delete the trials or make a copy of the experiment with a different name (File > Save As) and delete all trials.

▪Contact Noldus if you need to track more than 16 subjects per arena.