Auditory processing at two time scales by the cricketGryllus bimaculatus

Abstract

The acoustic display of many cricket species consists of series of pulses grouped into chirps, and thus information is distributed over both short and long time scales. Here we investigated the temporal cues that females of the cricket Gryllus bimaculatus used to detect a chirp pattern on a longer time scale than the fast pulse pattern. First, over a range of chirp and pause durations (100-400 ms), the duty cycle of the chirp pattern emerged as the most important cue for detection. The songs of males showed a distribution at lower duty cycles than preferred by females. The duty cycle also limited the responses of females at very short durations and pauses (below 80 ms). Second, by systematic variation of pulse and chirp periods of stimuli, an intermediate response field emerged that revealed the best responses of female crickets to patterns with amplitude modulations on both short and long time scales. On average, females also responded weakly to stimuli that contained amplitude modulations of only one time scale. Third, test patterns were constructed by addition of modulation frequencies rather than rectangular pulses. These tests showed that female crickets processed the chirp pattern in the time domain and tolerated noise levels up to a modulation depth of 50%. The combined evidence from all three approaches indicated inhibitory effects of unattractive patterns on both time scales. The fusion of short and long time scales during auditory processing by female crickets corresponded to a weighted AND-like operation of two processing modules, the pulse and the chirp filter.