Fig. 8

Fractions of four sample observations. Two are in agreement with the proposed heading model, and two are in disagreement. For each observation, three wing-beat periods are shown together with the frequency contents of the signal up to 1 kHz. Top left: short insect observation with a strong first overtone, similar to what would be expected from an insect entering the FOV at a normal angle. Top right: long insect observation with a strong first overtone, in disagreement with the proposed heading model. Bottom left: short insect observation with a strong fundamental frequency, in disagreement with the proposed model. Bottom right: long insect observation with a strong fundamental frequency, similar to what would be expected from an insect entering the FOV at a large angle and flying along it