Fig. 4. Deflection shapes of a female right tympanal membrane. TM was stimulated with a FM sweep signal. The oscillations are shown for four different driving frequencies (5, 10, 15, 20 kHz) at four different phases (0, 90, 180, 270°) along the oscillation cycle. For 10 kHz, the dominant frequency of male calling song, deflections are shown as profiles, as if looking at the tympanum from its side. Deflections are expressed as displacement gain following the colour scale. Red indicates outward tympanal deflections and green inward tympanal deflections. Note the difference in scale for each driving frequency. Orientation is indicated by a 3D space reference (D, dorsal; V, ventral; P, posterior; A, anterior; L, left; R, right). The horizontal black arrow indicates the direction of wave propagation. The ridge is visible as a black elongated teardrop (blue arrow) on the scan map.