Waveform Discrimination in the Electric Fish Eigenmannia: Sensitivity for the Phase Differences Between the Spectral Components of a Stimulus Wave

URN to cite this document:: urn:nbn:de:bvb:355-epub-21222
DOI to cite this document:: 10.5283/epub.2122

Kramer, Bernd ; Otto, Brunhilde

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Item type:	Article
Open Access Type:	Transfer of rights -1994
Journal or Publication Title:	Journal of Experimental Biology
Volume:	159
Number of Issue or Book Chapter:	1
Page Range:	pp. 1-22
Date:	September 1991
Institutions:	Biology, Preclinical Medicine > Institut für Zoologie > Alumni or Retired > Verhaltensbiologie und Verhaltensphysiologie (Prof. Dr. Bernd Kramer)
Keywords:	electrosensory; electroreception; signal waveform; phase difference; amplitude spectrum; sexual dimorphism; Eigenmannia
Dewey Decimal Classification:	500 Science > 570 Life sciences 500 Science > 590 Zoological sciences
Status:	Published
Refereed:	Yes, this version has been refereed
Created at the University of Regensburg:	Yes
Item ID:	2122

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Abstract

Eigenmannia lineata is a tropical South American gymnotiform fish that is both electrogenic and electroreceptive. Its electric organ generates a constant-frequency wave discharge (EOD) that is sexually dimorphic in waveform and harmonic content. Eigenmannia discriminates digitally synthesized, natural male
and female EOD waveforms of identical frequency and amplitude. Experiments were devised to investigate behaviourally the sensory mechanism of this discrimination.
Both the content in higher harmonics (as seen in an amplitude spectrum) and the waveform (phase spectrum) could provide the cues Eigenmannia uses for
discrimination. Five Eigenmannia were trained to discriminate artificially generated stimuli composed of the fundamental frequency,/!, and its harmonic, f2, of a
frequency twice that of /i and of weaker intensity (—13 to —3dB re / i ; a similar variation is found among the EODs of different Eigenmannia individuals). The rewarded stimulus, S+ (with a strong f2 intensity of — 3dB re /i), remained constant throughout the experiments. The family of negative (S—) stimuli all had a phase difference of 0°, that is, no phase difference, between their harmonics,
while the S+ stimulus had a phase difference of 90°. Therefore, all S— stimuli differed from the S+ stimulus in waveform, while one S— stimulus had an amplitude spectrum identical to that of the S+ stimulus.
All fish discriminated any S— signal tested from the S+ stimulus, including the S- stimulus with an identical amplitude spectrum, both when the test signals had
identical energy contents (that is, slightly different peak-to-peak amplitudes) and when they had identical peak-to-peak amplitudes (hence, slightly different energy
contents).
These results arc evidence for a true waveform (time domain) sensitivity of Eigenmannia. A sensory mechanism is proposed that enables Eigenmannia to assess the P/N ratio of a wave signal, that is, the duration ratio of positive (P) and negative (N) half-waves between zero-crossings of a stimulus cycle (the S+ and all S— stimuli, as well as female and male EODs, differ in this regard).

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