Fig. 4. The arista tip response in four male and four female flies. (A) Stimuli: superimposed frequency spectra of the acoustic random-noise stimulus at the position of the antenna during vibration measurements in eight animals and a spectrum of the background noise (BN). (B) Data reliability: frequency spectra of the coherence between the laser and the microphone signals during the same eight vibration measurements. Coherence can range between 0 and 1, with a value of 1 indicating the absence of unrelated noise. (C) Superimposed magnitude responses of the eight arista tips examined (males, blue traces; females, red traces). A response magnitude of unity (_vib/_air=1), where _vib is the vibration velocity and _air is the particle velocity, means that arista tip and air particles move at the same velocity. (D) Corresponding phase responses. A phase angle of +90° means that _vib leads _air by a quarter of an oscillation cycle.