Chemotaxis

Speed refers to the distance per second covered by the worm along its central axis.

• If the sign is positive, the worm is moving forward (head direction).
• If the sign is negative, the worm is moving backward (tail direction).

The speed is based on the position of the mid-point along the central axis. Image noise may affect speed measurements.

• Use Moving Average Speed or Smoothed Speed to reduce the effects of noise.

Moving average speed refers to the speed for a particular worm, averaged across a number of frames. The number of frames is known as the size of the moving window.

Using a moving average reduces the effects of noise, and also results in a latency in speed measurement.

• To adjust the number of frames, enter a different Average across value in the Moving Average Speed parameters.

Smoothed speed refers to the Moving average speed smoothed over a user-defined frame span using locally weighted polynomial regression[1][1] William S. Cleveland and Susan J. Devlin, Locally Weighted Regression: An Approach to Regression Analysis by Local Fitting, Journal of the American Statistical Association, Vol. 83, No. 403 (Sep., 1988), pp. 596- 610..

This method can remove outliers caused by worm model fitting error.

• To adjust the span, enter a different Span value in the Smoothed Speed parameters.