# Proximity

Definition

A discrete (state event) variable with two possible states, In proximity and Not in proximity:

▪The state is In proximity when the distance between the selected body points of the focal subject (Actor) and the body points of another subject (Receiver) is lower than a user-defined In proximity threshold.

▪The state is Not in proximity when the distance between the selected body points of the Actor and the body points of another subject Receiver is greater than a user-defined Not in proximity threshold.

▪The state does not change from the previous sample when the distance stays between the two thresholds.

If at least one of two subjects' selected body points is missing for more than three samples, the current Proximity state ends and the remaining missing samples are ignored.

Calculation

For each sample, the program calculates first the Distance between subjects, then it compares this value with the In proximity and Not in proximity thresholds to establish the state at that sample.

How to specify Proximity

1.Click the Add button next to Proximity.

2.In the Proximity tab, enter the In proximity and Not in proximity distance values that specify when the two subjects are considered in proximity to each other.

3.Under Calculate statistics for, select the state you want to analyze.

For example, select In proximity if you want to know how often or how long the subjects were close to each other. Select Not in proximity if you want to analyze when the animals were far from each other.

4.Click the Body points tab. Select the body points of the focal subject (Actor) you want to use to calculate proximity.

If you select two or three points, a drop-down list becomes available. Choose:

▪All selected points: A state is assigned only when all selected points are in that state relative to the Receiver (Proximity or Not in proximity). If body points are in different states, that sample is not used in analysis.

▪Any selected point: A state is assigned when at least one selected body point is in that state relative to the Receiver (Proximity or Not in proximity).

▪Each point: A state is defined for each point of the Actor. Results are displayed for each point separately.

5.Click the Receivers tab. Here, you specify the other subjects (Receivers).

Under Select, choose the subjects you want to calculate the distance from.
If you select two or more subjects, select one of the available options from the list:

▪All selected subjects: A state is assigned only when the Actor is in that state for all selected Receiver (In proximity / Not in proximity). If the Actor is in different states relative to different Receivers (for example, Subject 1 In proximity of Subject 2 and Not in proximity of Subject 3), that sample is not used in analysis.

▪Any selected subject: A state is assigned when the Actor is in that state for at least one Receiver (In proximity/Not in proximity).

▪Each subject: A state is assigned to each combination Actor*Receiver. Results are displayed for each Receiver.

6.Under Body points, select the body points of the Receivers you want to use to define proximity. If you select two or three points, select one of the available options:

▪All selected points: A state is assigned only when all selected points are in that state relative to the Receiver (in proximity/not in proximity). If different body points are in different states, the sample is not used in the analysis.

▪Any selected point: A state is assigned when at least one selected body point is in that state relative to the Receiver (in proximity/not in proximity).

▪Each point: A state is defined for each point of the Actor. Results are shown for each point separately.

7.Complete the procedure to add the variable. See Calculate statistics: procedure.

Notes

▪If the experiment is set to Only center-point detection or Color marker tracking, the Body points tab is absent. Calculations are based on the center point.

▪Any selected points: At any sample time, it is possible that the Actor's body points are in different states relative to the body points of the Receiver. For example, the Actor's nose point being In proximity of the Receiver's center point, and the Actor's center point Not in proximity of the Receiver's center point. In such cases when you select Any selected point (step 4 and 5 above), multiple states can be assigned to that sample.

▪Any selected Subjects: At any sample time, it is possible that the Actor is in different states relative to different Receivers. For example, Subject 1 being In proximity of Subject 2 and Not in proximity of Subject 3. In such cases when you select Any selected Subject (step 5 above), multiple states can be assigned to that sample. You can check multiple states occurring at one sample time when exporting the raw data (see Export the raw data (track and dependent variables). At a specific sample time, the value of the variable is 1 in more than one column, depending on which subject is in proximity of the Actor.

Application

Proximity can be used to study the behavioral interactions between individual animals, for instance the effects of individual housing vs. group housing on social behavior of rats (Spruijt et al. 1992. Physiology & Behavior 51: 747-752), or social isolation as a symptom of schizophrenia (Sams-Dodd, 1995. J. Neurosc. Methods 59: 157-167).