Pollimyrus adspersus discriminates the individually
variable waveforms of Electric Organ Discharges (EODs) of conspecifics of only 150–250 ms duration. We examined: (1) the discrimination threshold for artificially generated EODs of similar waveform, (2) the mechanism of signal analysis (spectral vs temporal) present, by determining the discrimination between different waveforms of identical amplitude spectra, and (3) the threshold field intensity and reach of discrimination. The triphasic
P. adspersus EOD waveform was artificially generated by
superimposing two Gaussians, one wide, the second narrow, inverted, and of threefold amplitude. The natural
variability among individual EOD waveforms was simulated
by phase-shifting one Gaussian relative to the other. The symmetrical waveform where the peaks of the two Gaussians coincided was used as a reference (phase shift=0, rewarded stimulus S+). Results were: (1) in foodrewarded conditioning experiments, trained fish (N=7) detected a phase-shift in artificial EOD stimuli as low as 2 ms (N=2 fish), 6 ms (N=1) and 10 ms (N=1). (2) All fish tested (N=3) discriminated between artificial EODs of identical amplitude spectra but different waveforms (hence, different phase spectra), demonstrating a temporal
mechanism of signal analysis. (3) The maximum reach of
waveform discrimination was 130 cm at 4.9 mVp-p/cm and
100 mS/cm water conductivity (test signal generated at
natural amplitude), that is, similar to the reach of EOD
detection. Therefore, among the three kinds of electroreceptor organ present in mormyrids, we consider Knollenorgane the relevant sensory organs for EOD waveform
discrimination
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