Fig. 4. Biotest design. (A) Example of a signal recorded when an ant walks on the sand surface above the membrane of the microphone. The arrow points to the signal reproduced in B; red lines represent leg strokes. (B) A close-up of the signal identified in the recording. (C) The mean signal used for pattern recognition. This signal was derived from the mean of 20 signals randomly extracted in 15 recordings. The green envelope indicates the standard deviation. (D) Example of pattern (i.e. mean signal) recognition in the recording shown in B. The blue curve is the smoothed envelope of the normalized cross-correlation function (CCF). The signals recognized using the maximum of the normalized cross-correlation function are indicated in B and D by vertical red lines.