Fig. 5. A model of correction. (A) Model trajectories were generated with a sine function scaled to approximate the characteristics of real trajectories. The tangent to the curve gives the orientation of the model ant, and the apparent height of the wall is defined as the vertical angle subtended by the portion of the wall that is viewed by the frontal retina of the model ant. The clockwise scanning phase, during which the ant turns towards the wall, ends when the apparent height of the wall reaches the stored value, and the counterclockwise scanning phase ends at a set angle. With training conditions, a starting y distance of 20 cm from a 20 cm high wall, the trajectory is parallel to the wall. With a 40 cm high wall and a starting y distance of 20 cm, the view on the frontal retina matches the required retinal height at a reduced deviation from the straight-ahead direction. Since rotation in the counterclockwise phase is unchanged, the trajectory veers away from the wall. Conversely, with a 40 cm y distance from a 20 cm high wall, the model ant rotates further towards the wall to match retinal height, and its course veers towards the wall. (B) The scanning model was tested in experiments in which ants were guided along the middle of a 60 cm wide channel by two 20 cm high walls. (C-E) Plots of the orientation at the end of each scan cycle for the training wall and the low (15 cm) and high (40 cm) test walls. The shaded areas in D and E indicate the predicted mode for the distribution based on the scan model and on the mode of the distribution for training runs in C.