Knowledge Base

Definition

The direction of movement of the nose, center or tail-base point of the current sample relative to a point of interest. See Define zones and Draw a point.

If your experiment is set to Center-point detection or Color marker tracking, calculations are based on the center point.

Calculation

Heading to point is calculated in a way similar to Heading. The difference is that for Heading to point the reference line is the line that connects the previous sample and the point of interest. For Heading, the reference line is the line parallel to the x-axis.

Heading to point for sample k is the angle α formed by the segment joining the samples k-1 and k, with the line connecting sample k-1 and the point P (a point of interest or the center of a zone).

Range

Heading to point ranges from -180° to +180°. The closer to zero Heading to point is, the straighter the subject moves toward the point. Negative values occur when the subject moves to the right of the point; positive values in the other case.

Below: Example of Heading to point with positive and negative values in a water maze test. The platform has been specified as a target point. The chart shows Heading to point in the Integrated Visualization (Analysis > Results > Integrated Visualization).

How to Specify Heading to Point

1. Click the Add button next to Heading to point.
2. From the Point of interest list, select the center of the Arena, center of gravity (COG) of a zone, or a point you defined in the Arena Settings.
3. Complete the procedure to add the variable. See Calculate statistics: procedure.

Notes

• If your experiment is set to Center-point, nose-point and tail-base detection, click the Body points tab and select the body points for which you want to calculate heading to point.
• The mean, standard deviation and variance are calculated with circular statistics. See Statistics available.

Applications

Use Heading to point to measure the subject's orientation relative to a point of interest.

• Morris water maze. Use Heading to point to determine the Heading angle error. The Heading angle error is usually determined after the animal has traveled a minimum distance, or after the first few seconds of each track. The Heading angle error at this point is the deviation from a direct line from starting point to center of the platform.

  Below: The Heading angle error (α) in a water maze. The first two samples of the track are displayed. The arrow indicates the release point.

  How? First, in the Data profile under Nesting choose Time, and select for example from 0 to 2 seconds. This means that analysis is done on the data points of the first two seconds of the track. Next, in the Analysis profile choose Heading to point and select the platform as point of interest. As Trial Statistic, choose Mean. For other water maze output variables, see also the EthoVision XT 19 - Application Manual.

• Novel object test. Use Heading to point to determine the subject's movement relative to an object. The assumption is that an animal is interested in a novel object when it is heading towards the center of the object.

Head Direction Definition

The smallest angle formed by the Head direction line of the current sample relative to a line parallel to the x-axis in the coordinate system. See also Head directed to zone.

The Head direction line is determined for each sample, based on the contour of the detected subject. It originates from the nose-point but it does not necessarily pass through the center-point. The angle α is assigned to the dependent variable Head direction for that sample.

Note: Head direction is not available if your experiment is set to:

• Center-point detection.
• Color marker tracking.
• Live Mouse Tracker.
• Center-point, nose-point and tail-base detection, with two subjects per arena tracked with Deep learning.

Examples

Below: An example of Head direction when exported in the raw data file (Analysis > Export > Raw Data; locate the Head direction column).

The angle is negative (-180°, 0] when the Head direction line departing from the nose-point lies left to the line parallel to the x-axis. The angle is positive [0, +180°] in the opposite case (in this example the x-axis is in the default position; it is horizontal and points to the right). The top-left picture shows the Head direction at the sample highlighted below.

Important: Note that the value of Head direction depends on the orientation of the x-axis set in the Arena Settings.

Head Direction Range

Head direction ranges from -180° to +180°. Therefore, values like -179 and +179 represent very similar orientations (head pointing to the left). Take this into account when interpreting the raw data.

How to Specify Head Direction

1. In the Analysis profile, click the Add button next to Head direction.
2. Complete the procedure to add the variable. See Calculate statistics: procedure.

Head Direction Notes

• Head direction is a very different thing than the Turn angle based on the nose point. The latter variable measures the direction of movement, not the orientation of the head. See Turn angle.
• You can check the head direction line during data acquisition. Click the Show/Hide button on the toolbar, select Track Features and make sure Head direction is selected. Next, let the animal move in the arena or play the video file. The real time Head direction values are shown in the Analysis Results and Scoring pane.
• The mean, standard deviation and variance are calculated with circular statistics. The mean Head direction represents the average orientation of the animal relative to the x-axis. See Statistics available.
• Head direction is calculated relative to the orientation of the x-axis you have chosen in the Arena Settings used for that trial. By default, the x-axis is horizontal and pointing to the right. If the x-axis is not horizontal or is pointing to another direction, Head direction is calculated based on that axis direction.
• Note: If you swap nose- and tail-base points, or interpolate those two points, the Head direction line is recalculated as the angle formed by the segment joining the nose-point and the center-point and the x-axis.
• If you edit the position of the nose-point or center point, the value of Head direction does not change.
• Be careful when interpreting values of Head direction relative to objects, for example two zones, or values extracted from different arenas.

  Example: In a mirror test, we want to measure the head direction of the fish, and compare the data between two arenas. The mirror is placed at opposite sides in Arena 1 and Arena 2. You can see that the same orientation relative to the mirror is measured with different angles:

  • For a negative angle in Arena 1: Angle in Arena 2 = Angle in Arena 1 + 180° (see the figure below, top).
  • For a positive angle in Arena 1: Angle in Arena 2 = Angle in Arena 1 - 180° (bottom).

  To compare the results between arenas, convert angles from Arena 2 to Arena 1 (or vice versa).

Head Direction Applications

Head direction is useful for studies of spatial orientation and searching behavior. For this you can, for example, use the average and variation in Head direction.

Source: EthoVision XT 19 Help, Noldus Information Technology