When the amplitude modulation of species-specific acoustic signals is distorted in the transmission channel, signals become difficult to recognise by the receiver. Tolerant auditory pattern recognition systems, which after having perceived the correct species-specific signal transiently broaden their acceptance of communication signals, would be advantageous for animals as an adaptation to the constraints of the environment. Using a well-studied cricket species, Gryllus bimaculatus, we analysed tolerance in auditory steering responses to non-attractive “Odd” and “Silent” chirps by employing a fine-scale open-loop trackball system. Odd chirps on their own did not elicit a phonotactic response. However, when inserted into a calling song pattern with attractive Normal chirps, the females’ phonotactic response towards these patterns was significantly larger than to patterns with Silent chirps. Moreover, females actively steered towards non-attractive Odd chirps when these were presented within a sequence of attractive chirps. Our results suggest that crickets employ a tolerant pattern recognition system that, once activated, transiently allows responses to non-attractive sound patterns. As pattern recognition modulates how crickets process non-attractive acoustic signals, the finding is also relevant for the interpretation of two-choice behavioural experiments.

Data were collected from an open loop trackball set up, which was manipulated by a tethered female cricket placed on top. Trackball movements were recorded using software designed in LabView 5.01 (National Instruments, London UK). The steering velocity of the crickets was calculated based on the output of the optical sensor and the lateral deviation over each presentation was obtained by integrating the velocity data. These were pooled to obtain a measure for the phonotactic response over a one-minute window 

Experiment 1 and 2 feature lateral steering deviations (in mm) to chirp types over the course of a minute. Experiment 3 features change in steering velocity (mm) between the onset of a chirp and peak response.