Abstract
The auditory stimulation method used in experiments on moth A cell(s) is generally believed to be adequate to characterize the encoding of bat echolocation signals. The stimulation method hosts, though, several biases. Their compounded effects can explain a range of discrepancies between the reported electrophysiological recordings and significantly alter the current interpretation. To test the hypothesis that the bias may significantly alter our current understanding of the moth's auditory transducer characteristics, papers using the same auditory stimulation method and reporting on either spiking threshold or spiking activity of the moth's A cells were analysed. The consistency of the reported data was assessed. A range of corrections issued from best practices and theoretical background were applied to the data in an attempt to re-interpret the data. We found that it is not possible to apply a posteriori corrections to all data and bias. However the corrected data indicate that the A cell's spiking may (i) be independent of the repetition rate, (ii) be maximum when detecting long and low-intensity pulses and (iii) steadily reduce as the bat closes on the moth. These observations raise the possibility that a fixed action pattern drives the moths' erratic evasive manoeuvres until the final moment. In-depth investigations of the potential bias also suggest that the auditory transducer's response may be constant for a larger frequency range than thought so far, and provide clues to explain the negative taxis in response to the searching bats' calls detection.
Highlights
It has been observed that moths apply a range of evasive manoeuvres that appear to depend on the distance of the moth to its main predator: the bat [1]
The intensity of the sound received by the moth is controlled by the experimenter by reading the measurement made by a sound pressure level (SPL) meter connected to a microphone
The method consists of four steps: (1) We first simulate the response of the SPL meter for the kind of pulses used in the experiment and for a series of emitted sound pressure levels, (2) we find a suitable regression that allows to convert the RMS deviation input to the SPL meter (dB SPL) readings into the sound pressure level that was received by the SPL meter’s microphone
Summary
It has been observed that moths apply a range of evasive manoeuvres that appear to depend on the distance of the moth to its main predator: the bat [1]. The ultrasonic pulses of the foraging bat vary during the chase: usually, the pulses’ intensity and duration decrease with the distance to the prey while pulses are emitted more frequently [4] This observation makes the moth’s intensity-triggered evasive behaviour even more unlikely. The intensity of the sound received by the moth is controlled by the experimenter by reading the measurement made by a sound pressure level (SPL) meter connected to a microphone This method has intrinsic biases that we will introduce as required through the course of this paper. Waters’ data [11] show that the SPL required to elicit a given spiking activity decreases as the pulse duration increases at a constant repetition rate The data from both studies are reported in figures 2 and 3. When analysing the properties of the sound stimulation method across all the papers reviewed, we formulate an alternative approach to minimize biases
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