Physical basis for auditory frequency analysis in field crickets (Gryllidae)

Summary1.The large posterior tympanic membrane in intact field crickets vibrates up to several hundred. Angstroms in response to sounds of the same frequency and intensity as the cricket's calling song. The mechanical response is linear (Fig. 3), shows a peak near 5kHz (Figs. 2, 5), and the membrane vibrates in the same simple mode in response to tones from 4 to 20kHz (Fig. 4).2.Reducing the movement of the large tympanic membrane by covering it with vaseline or by tearing holes in it (Fig. 7) causes a corresponding decrease in sensitivity of auditory interneurons (Figs. 6, 8).3.The measured vibration of the small tympanic membrane is of the same order of magnitude as that of the cuticle adjacent to the membrane and it shows no selective tuning.4.Introducing helium into the leg trachea changes the sensitivity of auditory interneurons. Thresholds near 5kHz increase by up to 30 dB and thresholds near 18kHz decrease by up to 13 dB (Fig. 9). This shift in tuning of the organ appears to be due to a change in the resonant frequency of the leg trachea.5.Acoustical calculations are consistent with our conclusion that the dominant tuning of the large tympanic membrane and of the organ to 5 kHz is due to a tracheal resonance.