Fig. 4. Turning responses to motion in the rear quarter-fields are non-directionally selective. Motion across the front half-field (A) or the constituent quarter-fields (B,C) generates turning responses that follow the sign of image motion (D). Front quarter-field motion produces saturated responses, thus the sum of responses (dotted red line in A) exceeds responses to half-field motion. (E) Motion across the rear half-field generates counterdirectional turning responses. However, responses to motion restricted to constituent quarter-fields show a sign inversion (F,G). Both clockwise and counterclockwise motion centered in a rear quarter-field triggers clockwise turns (G,H). Assuming bilateral symmetry, data from F are inverted and re-plotted here. As a consequence, the sum of rear quarter-field responses (dotted red line in E) does not approximate the response to half-field motion. This indicates non-linear processing of binocular motion information in the rear part of the visual field.