Figure 4. Aversive learning measured by an orientation test. Worms were suspended in a microdroplet and subjected to alternating air streams odorized with either OP-50 (non-pathogenic bacteria) or PA14 (pathogenic bacteria). A camera tracked the worm’s turning frequencies toward each other. Learning was seen when worms that had been exposed to PA14, later decreased their turning frequencies toward PA14, compared to worms that had not previously been exposed to PA14. The results are vertically arranged on raster plots where each dot represents one omega bend (a deep bend that is usually on the worm’s ventral side and changes the direction of its forward movement). Each row represents one cycle of the orientation test on one worm, and each worm was subjected to 12 cycles continuously in every test.