Fig. 6. Low-frequency (LF) electrical stimuli that recruit the ampullary electroreceptors more and the tuberous electroreceptors less than high-frequency stimuli (HF) are more efficient in eliciting post-pause responses. Means + S.E.M. of efficiency, (100), 100 electric organ discharges (EODs) after a pause were determined for three different types of stimulus: the mechanical stimulus (`Mech'; shown in Fig. 3), a low-frequency stimulus (a single cycle of a 2 Hz or a 10 Hz sine wave, selected with equal likelihood) and a high-frequency electrical stimulus (one cycle of a 1 kHz sine wave). LF and HF electrical stimuli had the same intensity (2.35 mV cm^-1 peak-to-peak). Data were obtained from 171 pauses in two fish (fish gc1, dark grey columns, 26, 35 and 20 measurements for mechanosensory, LF and HF stimuli, respectively; fish gc2, light grey columns, 30 measurements for each stimulus type).