Time-Characteristics of Communicative Sounds and Their Analysis in the Auditory System of Insects

This paper is concerned with the communicative code of insects, specifically crickets and cicades. Analysis of the calling songs of various species shows that they differ from each other in terms of amplitude modulation patterns (AMP) and there is direct evidence that the auditory system of insects is specialized in the analysis of AMP's. Some of the time characteristics of the calling songs, pulse rate, and chirp duration are highly stable and species specific whereas the unstable parameters, such as chirp rate, intensity, pulse form, and duration overlap broadly. The decoding of amplitude modulation patterns can be followed in the various stages of the auditory system of crickets from a peripheral stage with one group of LF receptors tuned to 4 to 6 kHz range and one HF group tuned to 10 to 16 kHz, the former dominating at low sensation levels. The neural impulse response rate is proportional to log-intensity. In the next stage 200 receptors converge in different combinations on a relatively small population of second order neurons with two specialized functions, the detection of pulse rate and chirp duration. The highest stage of the auditory system has not been studied directly. It probably classifies stimuli in terms of various temporal patterns and loudness guided by the center of sexual motivation.