01857nas a2200145 4500008004100000245015900041210006900200520126800269653003301537653002701570653002801597653001601625100002201641856004801663 1993 eng d00a‘Absolute steepness’ of ramps as an essential cue for auditory pattern recognition by a grasshopper (Orthoptera; Acrididae; Chorthippus biguttulus L.)0 aAbsolute steepness of ramps as an essential cue for auditory pat3 a

Male grasshoppers of the species Chorthippus biguttulus react to female songs with a characteristic turn towards the female. The probability of turning towards female song models was used to evaluate those parameters which are essential for a signal to be interpreted as female song.

1. The shape of sound pulses turned out to be most decisive; pulses with ramps rising gradually over 3 and more ms were efficient (Figs. 2, 3), whereas rectangularly modulated pulses evoked only weak responses and only when pulse intervals were between 3 and 5 ms (Fig. 2). The decline of a pulse did not influence its efficiency (Fig. 3). In particular, pulses with sudden onsets and gradual declines were as weakly effective as rectangularly modulated ones and thus remarkably less effective than pulses with ramp-like onsets (Fig. 4).

2. Intensity tuning curves suggest, that the absolute steepness of ramps (expressed as μbar/ms) is detected by the grasshopper nervous system (Figs. 6, 7), possibly by processing the delay in excitation onset of at least two receptor types differing in threshold sensitivity.

3. The sawtooth shape of pulses in female signals is suggested to be adaptive with respect to directional hearing.

10aAcoustic pattern recognition10aChorthippus biguttulus10aEnvelope of soundpulses10aGrasshopper1 avon Helversen, D. uhttp://link.springer.com/10.1007/BF00213685