Fig. 1. Modulation of the sLEOD by loading the stimulus-object with resistors. (A) The diagram illustrates the methodology employed. LEOD of Gymnotus carapo was recorded between an electrode adjacent to the skin and the closest base of a cylindrical object placed 2 mm away from the skin. The electrode was a 100 µm bare-tip insulated wire; the object consisted of a plastic tube 2 mm diameter () and 10 mm long with a carbon plug electrode in each opening. An external variable impedance z₀ was connected to the carbon plugs to modify the object longitudinal impedance. To evaluate impedance discrimination, a second impedance was alternatively connected using a timed switch. Changes in object longitudinal resistance resulted in marked changes in image contrast as shown by recorded sLEOD waveforms corresponding to open circuit (black), 22 k (red), 68 k (blue) and short circuit (gray; same color code throughout the figure). To align the traces we used as a time reference a far-field recording of the EOD that was not modified by the presence of our small stimulus-object. (B) sLEOD corresponding to the three first loads as a function of the sLEOD corresponding to open circuit. Note the small phase shift. (C) Spectral density of the same signals. The ordinate corresponds to the energy dissipated locally during eacy EOD. Note the hump in the high frequency shoulder of all spectra (arrow).