Hearing in insects: The nature of the response of certain receptors to auditory stimuli

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Abstract
Stimulation was given by a heterodyne oscillator coupled through an amplifier to a loud speaker, so arranged that frequencies between 30 and 11,000 cycles/sec. and intensity variations over a range of 140db. could be obtained. The use of a balanced amplifier and balancing potentiometer eliminated electrostatic from the loud-speaker and its leads. The platinum stimulating electrodes were in direct contact with the nerve supplying the anal cercus with its sensilla. In both the cockroach and cricket, there was no lower limit to the frequency to which the cercus would respond, the sensitivity at low frequencies being much greater than that of the human ear. The upper limit was about 3000-4000 cycles/sec. The responses of these nerves resembled those of the mammalian cochlear nerve in that at the lower frequencies the response was synchronized with the frequency during a sustained stimulus, though doubling in the frequency of the response sometimes occurred in the initial stages. At higher frequencies of stimuli, "frequency-halving" in the response indicated the existence of "alternation," and "equilibration" of both the slow and rapidly responding fibers could be demonstrated. Since the cerci are relatively insensitive to all but the lowest frequencies, it is probable that their main function is the detection of earth-borne vibrations in the cricket, of air movements in the cockroach. In the tympanal organ of the locust, no synchronization of response with stimulus frequency wag found, though the organ was very sensitive to intensity fluctuations at low absolute intensities. Since these organs are paired, they are thus adapted to the localization of sources of sounds which fall within the auditory spectrum.

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