Knowledge Base

Definition

A segment of track from sample A to sample B, where A and B are determined by a time, the value of another dependent variable, a Trial Control event, or the value of a signal from a hardware device.

Use Cases

Frequent cases:

• Group instances of behavior (e.g. Immobile) in a bout.
• Filter instances of behavior (e.g. Not moving) longer than one second.

See Examples of Free Intervals in the Analysis Profile.

Calculation

A Free interval is defined by a Start criterion and a Stop criterion. Depending on whether and how often the criteria are met within a track, a Free interval may result in zero, one or more instances of the interval within the same track.

NOTE Like all intervals defined with Nesting, a Free interval is left-closed [A, B). That is, the start sample A, not the stop sample B, is included in the analysis.

Multiple Instances of the Same Interval Definition

When you define a Free interval, this may result in zero, one or more (up to 2000) instances of an interval depending on where the Start and Stop criteria are met.

An instance of a free interval starts at the sample time when the Start criterion is met, and stops at the sample time when the Stop criterion is met.

A new instance is defined if the Start criterion and Stop criterion are met again, after the time in the track that the last Stop criterion was met.

NOTE Multiple instances of the same free interval definition cannot overlap. An interval is NOT defined when its start criterion falls within a previous instance of the same interval definition. For example, you define a Free interval that starts when the subject enters zone A, to 10 seconds after that time. If a new instance of In zone A occurs before the end of the interval, that instance of In zone is ignored.

Similarly, if you define a Free interval that goes from track start to when the external data Heart rate > 400, then one interval is defined, from Track start to the time when Heart rate reaches 400 bpm for the first time. This is because the "Track start" criterion is met once in each track, no matter how many times Heart rate reaches 400 bpm.

Multiple Free Intervals in the Analysis Profile

You can define multiple intervals in the Analysis profile by repeating the procedure below. The interval definitions are independent of each other; therefore the resulting intervals may be overlapping.

To Specify a Free Interval

1. In the Analysis Profile, under Custom Variables, click the button next to Free Interval.

2. Under Start criterion select the starting point of the interval:

   • Time. To select a time. For example, Track start (that is, the first sample in a track) or an Elapsed time after the track start (format: H:mm:ss.fff). For example 0:01:00.00 for one minute after the start. NOTE Track start corresponds to the first sample in the track (Recording time = 0.0), not the Trial time. For multiple-subject setups, Track start is the first sample of the animal detected first.
   • Dependent Variable. To select the time that a dependent variable has a specific value. For example, Distance moved >= 1 m, or frequency of In zone >=10. This list also includes behaviors scored manually and external data. See Free Interval Based on a Dependent Variable.
   • Trial Control. To select the time that an event in your trial control procedure occurs. For example, when a condition becomes true, or a command to a hardware device is given. See Free Interval Based on a Trial Control Event.
   • Hardware. To select the time that a hardware-related variable has a specific value. For example, when the number of food pellets dropped by a Pellet Dispenser is greater than 10. This option is only available when hardware devices are defined in your experiment. See Free Interval Based on Hardware.

3. Under Stop criterion select the end point of the interval. See above for most of the options.

   If you choose Time, and under Interval stop you choose Elapsed time, you have two options: after track start to stop the interval at a specific time after the track start (that is, the first sample in the track); after start event to stop the interval a specific time after the event selected as start criterion. Note that this "start event" is not the same as the start time of the resulting interval, if you set some time before the event (for example, 10 s before the frequency of In zone becomes 1). The "start event" is when the Frequency of In zone becomes 1. However, the interval starts 10 s earlier.

4. Select Ignore last interval if incomplete to ignore the interval when the stop criterion is not met. If you do not select this option, and the stop criterion is not met, EthoVision XT defines an interval up to the end of the track.

5. A free interval may occur once or more in a track (see above). To analyze each instance separately, select Calculate statistics per interval and enter the number of intervals you want to view in the results (1 to 2000). To be sure you view all intervals, enter a large number that exceeds the maximum possible number of instances per track. See Restrictions in EthoVision XT.

   To analyze all instances as one, de-select Calculate statistics per interval.

6. Complete the procedure to add the variable. See Calculate Statistics: Procedure.

Source: EthoVision XT 19 Help, Noldus Information Technology