Fig. 1. Circuit diagram and electrode array used to study the response of scalloped hammerhead and sandbar sharks to prey-simulating dipole electric fields. During each trial, one of the four electrode pairs (e1-e4) was activated with a weak electric current (6 µA), which generated a dipole electric field around the electrodes. Electrodes were spaced 1 cm apart, and each electrode pair was equidistant from an odor-delivery tube in the center of the plate. The electrodes were spaced symmetrically on the plate, and a 10 cm radius circle was drawn around the center of each electrode pair to serve as a frame of reference for subsequent video analysis. A line drawn on the plate through the dipole axis of each electrode pair was also used in video analysis to reference the orientation angle of the shark with respect to the dipole axis. Batt, internal 9 V battery; Ext, external power supply; Hi, high current pathway through the circuit; Lo, low current pathway through the circuit.