The Jamming Avoidance Response of High Frequency Electric Fish

Abstract

II. Quantitative Aspects 1. Using a frequency difference (LlF) clamp to maintain a stimulus and frustrate the normal escape from a jamming frequency, the response is found to be a. characteristic function of the LlF between stimulus and fish (Figs_ 2, 3, 4, 6). It is graded on both sides of a best Ll F of about 3 Hz ( = 0.3 % in Sternarchu8, 1.0 % in Eigenmannia). There is no systematic response when Fstimulus = Ffish , regardless of phase. 2. The J.A.R. is graded with intensity (voltage gradient) of the stimulus over a range of more than 100-fold; higher intensities cause some reduction (Fig. 5). The threshold for longitudinal stimulation under certain conditions is lower than 0.25 fJ. V (peak to peak)Jcm; for transverse stimulation as in most of the present experiments 0.5 fJ. V (peak to peak)/cm. 3. The best Ll F is the same when added to the fundamental of any harmonic (response detectable at least to the fifth) (Fig. 6). Stimulation around a subharmonic does not elicit the J. A. R. 4. A response to a small LlF, e.g. 0.2 Hz, can begin within < 1/4 cycle of the beat frequency and, without "hunting", shift in the correct direction. 5. Stimulating with an optimal beat-frequency by amplitude modulation (AM) of a stimulus at .Ffish' with an AM frequency of 3 Hz, can cause a response though it is confused as to sign. If the stimulus frequency unmodulated is at a Ll F = - 20 Hz and therefore almost ineffectual, A}1 at 17 Hz will cause a response upwards and at 23 Hz downwards (Eigenmannia). These results and the following suggest the fish performs the equivalent of a Fourier analysis and responds to sidebands according to their Ll F. 6. In a 300 Hz Eigenmannia, if an ineffective stimulus at 280 Hz (LlF = - 20 Hz) is frequency modulated (FM) sinusoidally at 17 Hz between peaks of about 274 and 286 Hz, the fish gives an upwards J.A.R. 7. By curarizing Eigenmannia to silence its electric organ we can apply a phase modulated stimulus - a carrier wave whose cycles are systematically phase shifted by a few degrees back and forth at a few Hz. This also causes a response, though only in one direction. 8. If a stimulus is slowly frequency modulated (FM