Fig. 9. Response probability (A) and phase distribution of response levels within the electric organ discharge (EOD) (B) for EOD shunts of lesser duration than 100 µs. (A) Responsiveness to novel feedback at the trunk/tail region decayed considerably when EOD current was shunted for less than 100 µs. In the experiments the switch was closed for a period that centered at the peak V₄ and was either 100 µs, 50 µs or 20 µs in duration. Experiments with fish 6 with electrodes positioned as shown in Fig. 5. Black bars, response probability at V₄. For each stimulus duration, response levels were additionally determined in (i) 20 controls in which the switch was closed after the EOD and (ii) in the absence of switch closure (20 tests). As response probabilities obtained under conditions (i) and (ii) showed no significant difference, data from (i) and (ii) were pooled and are displayed as grey bars. Responsiveness to 100 µs and 50 µs shunting, but not to 20 µs shunting, was significantly above the control level (P<0.001 and P<0.05, respectively; N=240 tests). (B) An attempt at a more detailed analysis of the response profile within the EOD using shortings that lasted only for 50 µs. As in Fig. 8, the horizontal position and width of the bars indicate the timing relative to the EOD (red trace). The height of each bar gives the response levels as obtained from a total of 1200 tests with fish 6. The dotted line was determined from pooling (i) 100 controls in which the switch was closed after the EOD and (ii) in the absence of switch closure (100 tests) (no significant difference in responsiveness). Only in the three phases around the final head-negative deflection (V₄) was the responsiveness significantly above control level (P<0.01).

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