Fig. 9. Changes in waveform and amplitude have additive effects. (A) Four loads, open circuit (generating the minimum rms value, black trace), short circuit (generating the maximum rms, 15 , grey trace) and two different impedances (generating the same intermediate rms value but very different waveform, a resistor of 21 k, red trace, and a capacitor of 10 nF, blue trace) were selected to test whether amplitude and waveform are independently evaluated by the fish. Right: the differences in amplitude and waveform of the signals compared by the fish. The differences in amplitude are shown by the main slope of the loop and the differences in waveform by its deviation from a straight line. (B—E) Each panel represents paired experiments in which the stimulus-object impedance was changed in either direction between open circuit and resistance (B), short circuit and resistance (C), open circuit and capacitance (D) and short circuit and capacitance (E). When resistive load were used, waveform changes were small (B,C) and novelty responses were only elicited by increases in sLEOD rms value. Consistently with the experiment shown in Fig. 7, the amplitude of the elicited novelty responses was graded with the increase in rms value. When large waveform changes (caused by a capacitive load, D and E) were associated with the same changes in rms value, the amplitude of the elicited novelty responses varied as if the rms value and the waveform were independently evaluated. The amplitude of the novelty response was relatively increased by a waveform change consisting of a reduction of the early slow-negative wave plus an increase and advance of phase of the late sharp-negative wave (compare the responses marked with filled symbols in D and E). When a similar waveform change was associated with a decrease in the rms value it provoked a small novelty response (compare E, open symbols, with C, open symbols). Finally, when increases in rms value were associated with opposite changes in waveform (reduction of the late negative wave and increase of the positive-negative slope), novelty responses were not elicited (E, filled symbols)

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