Fig. 2.

Hypothetical, perfectly cosine-tuned unit with its best direction (arrows) straight up. a, Cosine-tuned firing frequency. In the right triangle, firing ratef is equal to the cosine of the angle φ.b, Inversely cosine-tuned threshold force. In the right triangle the threshold force t is equal to 1/cosφ.c, Relation between threshold force and firing frequency. Threshold force is minimal for directions in which firing frequency is maximal and vice versa. d, The fact that threshold data in 2D can be fit by a line is consistent with a model in which 3D threshold data fall on a plane, and the best direction of the unit is given by the direction of shortest (i.e., perpendicular) distance between the plane and the origin (straight up arrow).