# Weighted movement to

Definition

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

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

Calculation

Formula:

▪If Dk - Dk-1 < 0:

WMTk= (Dk-1 - Dk) * abs(DSk - DSk-1)/(max (DSk, DSk-1))

▪If Dk-Dk-1 ³ 0, or DSk = 0:

WMTk = missing value

▪If DSk = 0, and DSk > Maximum interaction distance, then

WMTk = missing value

Where:

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

▪DSk-1, DSk is the distance between the subjects' body points for two samples (see Distance between subjects).

Notes

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

▪Weighted movement to 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. If R was the Actor, the point Q would be defined for the other subject (A in the figure) in the middle of the segment joining the two consecutive body points. In that case Dk would be longer than Dk-1, thus Dk - Dk-1 > 0 (i.e., R moves away from A), and the Weighted movement to would not be calculated. Instead, Weighted movement from would be calculated.

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

How to specify Weighted movement to

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

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

Following

A discrete (state event) variable that is scored when the subject (actor) follows a conspecific (receiver) within the specified distance. The actor's nose is oriented toward the receiver's center point within the specified angle. Both animals move faster than the specified value.

Parameters:

▪Minimum distance — The minimum distance between the two subjects.

▪Maximum distance — The maximum distance between the two subjects.

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

▪Minimum velocity of both subjects — Both subjects must move at least this fast for the event to be scored.

▪Maximum velocity of both subjects (Advanced) — Upper velocity limit for both subjects, to exclude fast transient crossings.