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The chirp rate in a territorial male cricket can be increased by playing chirps from a tape recorder. The increase is independent of the cricket's chirp rate before stimulation as long as the highest possible chirp rates are not yet reached (Figs. 5, 6, 8), but the size of the increase depends on the chirp rate of the stimulus used. After the end of stimulation the chirp rate returns exponentially to its previous level with a half Me of about 20 seconds.

A momentarily silent cricket is more likely to start chirping at the beginning of stimulation and less so after a few minutes of stimulation than would be expected without stimulation. The chirp rate reached in these cases is higher the sooner the cricket starts chirping during stimulation (Figs. 9, 10, 11). These regularities can easily be deduced by allowing the chirp activity to have negative values if no chirps occur (see discussion).

The following phenomena were found when chirps were played to a territorial male cricket:

1. A stimulus chirp not coinciding with a chirp of the cricket inhibits chirping from the 40th to the 180th msec following the onset of the stimulus.
2. It additively increases the chirp rate of the cricket by approximately 0.3 chirps/sec.
3. About 99% of this additive increment decays with a half life period of approximately 2 sec (phasic effect), the rest decays with a half life period of approximately 140 sec (tonic effect).
4. The effects of successive stimulus chirps are superimposed, however neither the phasic nor the tonic total increment ever passes a particular upper limit. If the total tonic increment becomes large enough, a previously silent cricket will start to chirp.
5. If chirps are played at a sufficiently high rate, the cricket tries to chirp in alternation.

The effect of acoustic signals on the control of chirp production has been investigated using the insect's own chirp to trigger artificial sound signals (100 msec, 7odB, 12 or 15 kHz) at predetermined phases of the chirp cycle. The signals appear to reset the phase of the chirp rhythm generator, and signals given late in the cycle are followed by the greatest phase shifts. The signals may also have excitatory after-effects which are usually small, but can summate to give a slow, longer lasting increase in chirp rate. This appears to happen during alternation with a natural or artificial partner.