Fig. 3. (A-C) Examples of the responses of a TS1 unit (A), a highly directional TS2 unit (B), and a TS3 unit (C) to a sphere moving from anterior-to-posterior (left) or from posterior-to-anterior (right). Top traces in A-C show original recordings. In each case raster plots of the responses to 10 stimulus presentations are also shown. The two vertical lines in the bottom traces indicate the positions of the trigger contacts. The fish symbol indicates size, location and orientation of the fish relative to the path of the moving sphere between trigger contacts. Note that sphere movements were made manually and were normalized to a length scale so that the trigger contacts indicate the length of the path (23.8 cm). Mean sphere velocity was 10.7 cm s^-1 in A, 9.8 cm s^-1 in B and 9.9 cm s^-1 in C. Arrows 1-4 in the top traces of C mark the time when the PIV images shown in D were taken. Vertical scale bars, 50 µV (A), 100 µV (B,C). (D) Velocity vector plots of vertical particle motions. The flags indicate direction and velocity of water motions. The width of each image is 58 mm, the size of each interrogation area (subimage that was subjected to the correlation procedure) is 5 mmx5 mm with an overlap of less than 50%. Scale bar, 10 mm s^-1.