Weighted movement from

Definition

The distance-weighted change in distance between subjects, when a subject (Actor) moves away from another subject (Receiver).

Weighted movement from (WMF) is a continuous variable, and is always positive. It is calculated only when the state of the Actor is moving from the Receiver (see also Relative movement).

Calculation

Formula:

▪If D_k - D_k-1 > 0, then

WMF_k = (D_k - D_k-1) * abs(DS_k - DS_k-1)/(max (DS_k, DS_k-1))

▪If D_k - D_k-1 £ 0, or DS_k = 0, then

WMF_k = missing value

▪If DS_k-1 > Maximum interaction distance, then

WMF_k = missing value

Where:

▪D_k-1, D_k is the distance between the Actor's body point and the interpolated point of the Receiver calculated for two consecutive samples.

▪DS_k-1, DS_k is the distance between the subjects' body points for two samples.

In the figure below, A is the body point of the Actor, R of the Receiver. Q is the interpolated position between the Receiver’s body points at samples k and k-1.

 

Notes

▪Weighted movement from is equal to the absolute value of Net weighted movement, taken for those samples in which the value of NWM is negative (the focal subject moves away from another subject).

▪Weighted movement from is weighted by the distance between two subjects. Changes in positions of subjects which are at a large distance from each other have a lower weight, so they can be distinguished from movements at close distance, which have a different biological meaning.

▪From the figure above one can see that the outcome depends on which of the two interacting subjects is considered as Actor and which as Receiver. This is because formula takes possible differences in speed of approach of the subjects into account. In that case, the difference D_k-D_k-1 is positive, therefore Weighted movement from R is calculated. If R was the Actor, the point Q would be defined for the other subject in the middle of the A_k-1-A_k segment. In that case D_k would be shorter than D_k-1, thus D_k - D_k-1 < 0, and the dependent variable would not be calculated.

▪This dependent variable is not a speed, as time is not involved in its calculation. However, the parameter is quadratically sensitive to movement of the subject.

How to specify Weighted movement from

1.Click the Add button next to Weighted movement from.

2.In the Weighted movement From tab, under Maximum interaction distance, enter the distance above which you do not want to consider the subjects as interacting. (Default: 50 cm/16.69 inches)

3.Click the Body points tab. Select the body points of the focal subject (Actor) you want to use to calculate the dependent variable. If you select two or three points, results are calculated for each point separately.

4.Click the Receivers tab.

▪Under Select, choose the subjects you want to consider as Receivers.

▪Under Body points, select the body points of the subjects selected above. If you select two or more subjects and points, results are calculated for each combination separately.

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

Notes

▪Weighted movement from is calculated for all the subjects selected in the Data profile. Each subject displayed on the rows of your result table is considered as Actor. The subjects displayed on the columns are the Receivers.

▪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.

Application

Weighted movement from can be used as an objective measure for the intensity of avoidance (Spruijt et al. 1992. Physiology & Behavior 51, 747-752).

 

Leaving

A discrete (state event) variable that is scored when the subject (actor) moves away from a conspecific (receiver) within the specified distance. The angle between the actor's center-nose vector and the receiver's center point is less than specified. The actor is moving at a velocity higher than the specified value.

Parameters:

▪Minimum distance — The minimum distance between actor and receiver.

▪Maximum distance — The maximum distance between actor and receiver.

▪Maximum orientation angle — The maximum allowed angle between the actor's center-nose vector and the direction toward the receiver.

▪Minimum velocity of actor — The actor must move at least this fast.

▪Minimum velocity of receiver (Advanced) — Minimum receiver velocity threshold.

▪Maximum velocity of both subjects (Advanced) — Upper velocity limit for both subjects.