Knowledge Base

Definition

A discrete (state event) variable, related to one of the body points, with two possible states, High acceleration and Low acceleration. At any sample time:

• The state is High acceleration when the running average acceleration exceeds the High acceleration above threshold.
• The state is Low acceleration when the running average acceleration is below the High acceleration above threshold.

The running average acceleration is calculated according to the formula for Acceleration for each sample, over the number of samples specified by the Averaging interval.

How to Specify Acceleration State

1. Click the Add button next to Acceleration state.
2. In the Acceleration State tab, enter the following:
   • Averaging interval. This is the number of samples over which the running average acceleration is based. The default value is 1, that is, acceleration is not smoothed before calculating the Acceleration state variable.
   • High acceleration above. The acceleration above which the animal must be considered in the High acceleration state.
3. Under Calculate statistics for, select the state you want to analyze, High acceleration and/or Low acceleration.
4. Under State duration threshold, next to Exclude instances shorter than, enter the minimum duration of the Acceleration state (see the note below).
5. In the Body Points tab (if present), select the body points for which you want to calculate Acceleration state.
6. Complete the procedure to add the variable. See Calculate statistics: procedure.

Notes

• Enter zero as High acceleration above to distinguish between positive and negative acceleration.
• To find the optimal High acceleration above threshold, run a few test trials and in the Integrated Visualization plot the values of Acceleration and Acceleration state. Adjust the threshold value in such a way that the state High acceleration is scored only when the animal shows bursts of rapid movement in the video.
• We advise you to use an Averaging interval greater than 1 to remove the effect of random changes in velocity between consecutive samples that would result in false transitions between Low and High acceleration. However, the greater the Averaging interval, the longer the delay in the determination of a state transition. See Averaging interval.
• The State duration threshold is the minimum duration of the set of consecutive samples with Acceleration above (or below) the High acceleration above threshold required in order to be scored as the corresponding state. If the set of samples passes the threshold, the samples are scored as the state. If the set of samples does not pass the threshold, the previous state ends, but no new state is defined. Use this option to filter out brief transitions between High and Low acceleration caused by body-point jitter or noise detection.

Applications

Use Acceleration state to mark bursts of rapid movement, like swimming bursts in fish.

Activity: Definition

The dependent variable Activity is only available when you selected Activity analysis in the Experiment Settings and you track only one subject per arena. Activity gives the percentage of changed pixels in the entire arena between the current sample and the previous sample.

Calculation

See step 1 and 2 in Activity state for information on how this percentage of changed pixels is calculated. With the dependent variable Activity state, you can calculate how much time and how often your subject was inactive, moderately active and active, and highly active. With the dependent variable Activity, you can calculate the average activity of your subject.

How to Specify Activity

1. Click the Add button next to Activity.
2. Under Outlier filter, select the Averaging interval. This is the number of samples over which the running average mobility is based. The default value is 1, that is, the current value of Activity is only based on the current image. See Averaging interval. See Activity state for more information.
3. Complete the procedure to add the variable. See Calculate statistics: procedure.

Source: EthoVision XT 19 Help, Noldus Information Technology