Figure 7. The proposed path integration circuit is resilient to disturbance.

(A) Performance during increasingly longer outbound journeys and increasing neural noise. Closest distance to nest during homing (mean ± SD from 1000 runs) plotted against length of outbound journey. (B) Distribution of angular deviations from true home after initiation of steering (10° bins, 1000 trials) for different noise levels (colors as in A). (C) Deviation from the best possible route (straight line) during homing (10% noise). C: distance covered towards the nest after L steps, (L = straight-line distance to nest); L/C = path tortuosity (average: 1.150). (D-H,I) Responses to disturbances reveal the robustness of the circuit. Plotted is the closest distance to home during homing after a 1500 step random outbound route against different types of disturbances (mean ± SD). Dashed grey line: 20 step home range used to illustrate successful homing. (D) stochastic noise in the sigmoids of each neuron. The 0.1 level was also used for all remaining trials (blue curves; green curves are without sigmoid noise). (E) Effect of randomly varying synaptic weights. (F) Effect of shifting clockwise and counter-clockwise preference angles of compass signal. Orange line: Value found for Megalopta compass neurons (Figure 1). (G) Effect of deviation of translational optic-flow preference axis from the bee’s body axis in TN2-neurons. Orange line: Average value obtained in Megalopta TN-neurons (Figure 3). (H) Effect of actual speed exceeding capacity of speed neuron (TN2) coding range. Right: Example routes show that the agent undershoots, but maintains the correct heading, when speed neurons saturate during outbound route. (I) Effect of low-pass filtering of the speed signal (as found for TN1-neurons). Right: Example of how a smoothed speed signal affects homing.