Fig. 7. Typical measurement data of the force response of the bees. The red lines represent the raw measurement data of the vertical force (F₀), without any compensations. The source of fine oscillations in F₀ is certainly the wingbeat of the bee; the oscillation frequency is approximately 150 Hz in common throughout A-D. The broken blue lines represent the filtered data of F₀. The bold broken green lines represent the visual stripe position. The upward direction is defined as the positive direction for both F₀ and z_v. (A) Visual oscillation frequency is 0.9 Hz (5.6 rad s^-1). The phase of F₀ obviously precedes that of z_v. (B) Visual oscillation frequency is 1.8 Hz (11 rad s^-1). The phase of F₀ still precedes that of z_v. (C) Visual oscillation frequency is 3.6 Hz (22 rad s^-1). The phase difference between F₀ and z_v is small. (D) Visual oscillation frequency is 7.4 Hz (46 rad s^-1). The phase of F₀ obviously lags behind that of z_v. Although the variation in the phase through A-D is clear, the amplitude of F₀ is relatively constant.