‘Frequency Discrimination’ in Insects: a New Theory

Abstract

IT has long been known that some at any rate of those insects which possess tympanic organs are able to discriminate between sounds which differ by a factor other than intensity. Regen¹, for example, showed that a long-horn grasshopper, Thamnotrizon apterus, could distinguish the stridulation of its own from that of related species, and either from various artificial noises. No insect has any peripheral mechanism which would permit harmonic analysis after the manner of the mammalian cochlea. The only alternative basis for discrimination is that different sound qualities shall be represented in their auditory nerves by different temporal patterns of afferent nervous impulses. But here a limit is imposed by the refractory period of the nerve fibres, and frequency discrimination on this basis would only be expected to be possible for frequencies up to a few hundred cycles per second.