Fig. 5
Computer simulation of acidic pH avoidance behavior using a two-distinct-threshold model. a Schematic drawings of the locomotion of the model worm. The position of the model worm (Pn, Pn+1,…) and the pH sensor of the worm (Sn, Sn+1,…) at each time point is shown by filled and open circles, respectively. b–d Behavior of the model worm. Results are shown as in Fig. 3c (left) and Fig. 4 (center and right). Right and dark green represents reversal and curve, respectively. From b to d, acidic pH gradient used for simulations was as same as that shown in Fig. 3a, left to right. Conditions for (d) were used to obtain an optimal set of parameters. Parameters used were α c 0.5, β c 4.3, α r 0.5, β r β c  − 1.6, φ c 30, Δφ c 10, initial position of the model worm: <−2.0 (see Methods in detail). The ratio of reversal had a positive correlation with the angle in all conditions (R > 0.9, p < 0.01)