Knowledge Base

Introduction to Trial Control (Continued)

For a Reference box. Control is passed to the Sub-rule Begin box. The Reference box makes the sub-rule active. The Reference box stays active until the last sub-rule repeat is completed. Next, the Reference box makes the sub-rule inactive and passes control to the box that follows. Next, the Reference box becomes inactive.

The events marked in italics above are those you can define in the Analysis profile and analyze or visualize in a chart. When a box becomes active, the previous one becomes inactive.

Schematic Representation of Trial Control Execution

The following steps describe how Trial Control Instructions are executed, using an example of a Start-Stop trial rule:

1. Tracking starts, either manually or because a previous condition has been met.
2. Control passes to a Condition box (for example "Is mouse on top of Shelter?"), which becomes active. The condition is evaluated.
3. The Condition is met (becomes true).
4. Control passes to the next box. In this case, it is an Action. Actions are taken immediately (but see the note below on actions on hardware devices).
5. The Action box becomes inactive, and the next box becomes active.

For clarity, certain steps have been placed separately. In reality, the software is so fast that when a condition becomes true it also becomes inactive at the same sample time, and control passes to the next box.

• Hatched Outlines: Condition box becomes active.
• Dark Outlines: Condition becomes true or Action is taken.
• Pale Outlines: Box becomes inactive.

Evaluation of Trial Control Boxes

Boxes combined in parallel using operators are evaluated at about the same time, in random order. This means that you cannot establish which condition is evaluated or which action is taken first.

When your trial control is complex, for example when it includes sub-rules or conditions combined with operators, it is possible that two or more Trial Control boxes are evaluated at the same sample time.

When a condition based on a dependent variable is evaluated (and therefore may or may not be met) also depends on the statistic used.

If two or more boxes are evaluated at the same time, an action on a hardware device is taken only after all active boxes that must be evaluated have been evaluated.

Time Plot of Trial Control Events

When tracking starts, the Action "Start track" becomes active (1st line) and immediately inactive (2nd line) as control passes to the next box. The condition "On top of Shelter?" becomes active (3rd line) and immediately false (4th line) since the animal is not in that zone. When the animal enters the zone, the condition becomes true (5th line), and becomes immediately inactive (6th line) as control passes to the next box. The action becomes active (7th line) and immediately inactive (8th line) as the command "drop a pellet" is sent to the pellet dispenser.

If the next box to be evaluated contains a condition that is fulfilled immediately, the program passes control to the next box. Therefore, within one sample time the program can pass control to two or more boxes to the right.

When you stop the trial or the Maximum trial duration has been reached, all Trial Control boxes are deactivated.

When the Rule End box of the Start/Stop trial rule is evaluated for an arena, data recording stops for that arena. From that moment, Trial Control is deactivated for that arena, even in those sub-rules that were ongoing in the meantime.

A trial stops when trial control is deactivated in all arenas.

Actions on Hardware Devices

A command is sent to a device after all boxes that must be evaluated have been evaluated. However, it may take some time for the outcome to be seen. For example, when a pellet dispenser is almost empty it may take a few seconds before a pellet is released.

Important: When two or more actions on hardware devices follow each other, it is possible that they are evaluated at the same sample time. This happens because the computer is fast enough to analyze multiple Trial Control boxes in the sample interval. To make sure that actions are taken in the correct sequence and do not interfere with each other, add a Time condition between the action boxes, so after the first action is carried out EthoVision XT waits for a short time (for example, 0.1 s) before carrying out the next one.

Sub-Rules

A sub-rule is completed when the Rule End box has been evaluated, or when it is interrupted.

If two or more sub-rules are evaluated at the same time, it is not possible to establish which sub-rule is evaluated first at a specific sample.

Trial Control in Multiple Arenas

If your experimental setup includes two or more arenas, Trial Control is applied to each arena separately. This means that, if a condition is met in one arena, EthoVision XT takes the corresponding action in that arena, not the others.

Example: The setup includes four cages, each defined as an arena. A Trial Control "In zone" condition has been defined so that tracking starts when the animal is first detected in the arena. When you first put an animal in Arena 2, the condition is met in this arena and tracking starts for that arena. When you release the second animal in Arena 4, two seconds later, tracking in that arena starts two seconds later than in Arena 2.

The advantage of Trial Control in multiple arenas is that you can put one animal at a time into the arenas, and EthoVision XT will start tracking in each arena at the appropriate moment.

If your setup includes multiple arenas, you cannot define a condition or action specific to one arena. This means that the zones and hardware devices specified in the condition or action must be present in all arenas, and have the same name.

If a zone or hardware device is not present in an arena, and a condition is based on that zone or device, Trial Control cannot progress for that arena. Therefore, tracking does not stop unless you set a maximum trial duration or tracking reaches the end of the video.

Source: EthoVision XT 18 - THC - Trial and Hardware Control, Noldus Information Technology