# Optimize nose-tail base detection

Because of the way the nose- and tail base points are found, nose-tail base detection is much depending on the quality of the video image and the experimental setup. Before using this feature, please check the following guidelines:

Conditions related to the Arenas

▪Light: Light conditions must be equal across the arena. Try to remove shades, light spots and reflections. For proper detection, the subject's body contour must be kept as constant as possible across the whole arena.

▪Subject/background contrast: The color of the subject and of the background must be contrasting enough to get a full and clear body contour.

▪Video quality: Noise and interference reduce the proportion of samples which are correctly detected.

▪Noise reduction: The Video Pixel Advanced detection settings: Smoothing function can sometimes help getting a more appropriate body contour. However this is of little use if the video has too much noise or too little contrast.

▪Areas hidden to the camera view: When the animal enters or exits areas hidden to the camera (for instance, a shelter), nose-point and tail-base are wrongly assigned.

▪Number of arenas: Reliable tracking of nose and tail-base is limited by the size of the video image. You can mix maximally four camera images like in the case of a group of PhenoTypers, with good results.

Conditions related to the Subjects

▪Subject's apparent size: The subject must be large enough to get a constant body contour. Small animals and large arenas pose detection problems with nose- and tail-base points. When you mix the image of multiple cameras with a quad unit, like in the case of a group of PhenoTypers, a group of 4 cameras gives good results. When mixing 16 PhenoTypers, the apparent size of the subject is generally too small.

▪Subject's color variation: For hooded rats, both the flanks (white) and the head (dark) must contrast with the background, otherwise detection of body contour is sub-optimal. In the Detection Settings, next to Subject color compared to background select Brighter and darker than background. You can also try the Differencing detection method instead of the Subtraction methods.

▪Subjects in a water maze: Tracking nose- and tail-base points in a water maze is impossible because the tail-base is under the water, and it is not possible to obtain a proper body contour.

▪Subject's behavior: Immobile animals are hard to track because their body contour differs from that of a mobile animal. Nose-points are therefore hard to detect.

Important choices

▪Tracking live vs. from video files. We recommend to track from video files if you use one of the methods named For occlusions. Tracking live requires high processor load, which may result in many missing points, especially when you use multi-subject tracking and multiple arenas simultaneously.

▪When tracking from video files. Keep the DDS (Detection determines speed) option selected, unless you score behaviors manually.

▪Missing tail-base points: The high percentage of missing tail-base points is an indication of poor detection. The higher this percentage, the greater the probability that the nose-point is not placed in the correct location. To estimate the proportion of missing tail-base points, run some test trials and visualize the Sample list in the Track Editor screen. You can also calculate the Number of samples as a statistic for a dependent variable such as Velocity for the nose point.

In practice…

The contour of the blob detected as subject is crucial for proper detection of nose- and tail-base points. If only part of the subject is detected, EthoVision XT may swap the pixels assigned as nose-point and tail-base.

Or the nose-point is not placed on the subject's nose tip (for clarity, the nose point is shown together with the Head direction):

If you use a Subtraction method, select a wider range of gray scale values or, for Differencing, adjust the sensitivity to increase the number of pixels detected as subject.

Detection of the tail depends on which method you use for detecting the body points. See Methods for estimating the body points

▪When you use the Any species / Default method for estimating the body points, make sure that the tail is fully detected.

▪When you use one of the Rodents method, remove the tail from the detected subject using the Erosion then the Dilation filter. See Subject contour for nose-tail base detection