Knowledge Base

Definition

A discrete (state) variable with four possible states: Moving to, Moving from, No relative movement, and No interaction.

• The state is Moving to when the focal subject (Actor) is moving towards another subject (Receiver).

  NOTE: An Actor is the subject listed on the rows in the statistics table, or in the Integrated Visualization at the left side of each chart. Other subjects in the same arena are Receivers.

  NOTE: The term moving refers to a subject moving faster than a specified minimum velocity.

• The state is Moving from when the Actor is moving away from the Receiver.
• The state is No relative movement when two subjects are not moving relative to each other.
• The state is No interaction when the distance between subjects is great enough that they can be considered as not interacting.

Calculation

1. To calculate the Relative Movement for sample k, the body points of the Actor and the Receiver must be known for sample k and k-1.
2. The middle point Q is determined on the segment that joins the body points of the Receiver for samples k–1 and k.

   In this example, A is the body point of the Actor, R of the Receiver. Q is the interpolated position of the Receiver's body point.

3. The distance between the Actor's body point and Q is calculated for samples: Dk and Dk-1, respectively.
4. The state of Relative Movement is determined:
   • If Dk > Dk-1: Moving from
   • If Dk < Dk-1: Moving to
   • If Dk = Dk-1: No relative movement
   • If Dn > Maximum interaction distance (user defined): No interaction
   • If the velocity of the Actor is lower than the Minimum velocity (user defined): No relative movement

From the figure above, one can see that the outcome depends on which animal is considered as Actor and which as Receiver. If the other subject is considered as the Actor, the point Q is defined in the middle of the segment joining the Receiver's points Rk-1 and Rk. Note that Dk is longer than Dk-1. Therefore, this subject, when considered as the Actor, is Moving from the other subject.

How to Specify Relative Movement

1. Click the Add button next to Relative movement.
2. In the Relative Movement tab:
   • Next to Maximum interaction distance, enter the distance above which you do not want to consider the subjects as interacting (Default: 50 cm / 16.69 inches).
   • Next to Minimum velocity, enter the minimum velocity of the Actor for it to be considered as moving from or moving to the other subject. Note that the velocity of other subjects does not count here.
   • Under Calculate statistics for, select the states you want to consider. By default, all states are selected.
3. Click the Body points tab. Select the body points of the focal subject (Actor) you want to use to calculate relative movement.

   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 (moving to / from / no movement / no interaction). If body points are in different states, the state is not assigned to that sample.
   • Any selected point: A state is assigned when at least one selected body point is in that state relative to the Receiver (moving to / from / no movement / no interaction). See the note below.
   • Each point: A state is defined for each point of the Actor. Results are shown for each point separately.
4. Click the Receivers tab. Here, you specify the other subjects (Receivers). Under Select, choose the subjects. 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 Receivers (moving to / from / no movement / no interaction). If the Actor is in different states relative to different subjects (for example, Subject 1 Moving to Subject 2 and Moving from Subject 3), the state is not assigned to that sample.
   • Any selected subject: A state is assigned when the Actor is in that state for at least one Receiver (moving to / from / no movement / no interaction).
   • Each subject: A state is assigned to each selected subject as a separate Receiver. Results are shown for each Receiver.

   Under Body points, select the body points of the subjects selected above. If you select two or three points, select one of the available options:

   • All selected points: A state is assigned when the Actor is in that state relative to all selected points of the Receivers (moving to / from / no movement / no interaction). If the Actor is in different states relative to different Receiver body points, the state is not assigned to that sample.
   • Any selected point: A state is assigned when the Actor is in that state relative to at least one selected body point (moving to / from / no movement / no interaction).
   • Each point: A state is defined for each body point of the Receiver. Results are shown for each Receiver body point separately.
5. Complete the procedure to add the variable. See Calculate Statistics: Procedure.

Notes

• All / Any selected points: At any sample, body points of one subject can be in different states relative to another subject's point. Consider an example where the center point of Actor A (circles) is moving to Receiver R, while the nose point of A (triangles) is moving from the Receiver.
  • Selecting All selected points gives no unique state for Relative Movement at sample k.
  • Selecting Any selected points gives the state Moving to for the center point and Moving from for the nose point at sample k.
• Any selected subject: At any sample time, it is possible that the Actor is in different states relative to different Receivers. For example, Subject 1 Moving to Subject 2 and Moving from Subject 3. In such cases when you select Any selected subject, multiple states are assigned to that sample. You can check multiple states being assigned to one sample time when exporting the dependent variable. At a specific sample time, the value of the variable is 1 in more than one column of the export file. In the example above, the columns for Moving to and Moving from will both show 1 in the corresponding sample row.
• If your experiment is set to Only center-point detection or Color marker tracking, the body point options are absent. Calculations are based on the center point.

Source: EthoVision XT 19 Help, Noldus Information Technology