Knowledge Base

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 ≥ 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.
• 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.

Additional 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, 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.

Side by Side Definition

The focal subject is side-by-side with another subject. The latter is named receiver in EthoVision XT.

Two categories are defined, based on how the subjects are oriented relative to one another:

• Same direction: the focal subject and the receiver are side by side and pointing to the same direction.
• Opposite direction: the focal subject and the receiver are side by side and pointing to different directions.

This variable is available in experiments set to Center-point, nose-point and tail-base detection. See Tracked Features.

Side by Side Calculation

• For Side by side, same direction:
  • EthoVision XT finds the samples where both the distance between the nose-point of the focal subject and the nose-point of the receiver and the distance between the tail-base point of the focal subject and the tail-base point of the receiver are below the specified threshold (default: 5.26 cm).
  • If the two vectors formed by the tail-base point and the nose-point of each subject point to the same directions (that is, the dot product of the two vectors is positive), then Side by side, same direction is scored for that sample.
• For Side by side, opposite direction:
  • EthoVision XT finds the samples where both the distance between the nose-point of the focal subject and the tail-base point of the receiver and the distance between the tail-base point of the focal subject and the nose-point of the receiver are below the specified threshold (default: 5.26 cm).
  • If the two vectors formed by the tail-base point and the nose-point of each subject point to opposite directions (that is, the dot product of the two vectors is negative), then Side by side, opposite direction is scored for that sample.

How to Specify Side by Side

1. Open an Analysis profile and in the Dependent Variables panel, under Social, click the Add button next to Side by side.
2. Under Threshold, enter the maximal In proximity distance acceptable between the two subjects' body points (nose to nose or nose to tail-base).
3. Under Calculate statistics for, select the option Side by side, same direction, or Side by side, opposite direction, or both.
4. Complete the procedure to add the variable to the Analysis profile. See Calculate statistics: procedure.

Side by Side Note

Side by side is similar to Proximity, however the latter cannot tell whether the subjects are oriented in the same or different directions.

See also:

• Proximity

Source: EthoVision XT 19 Help, Noldus Information Technology