Figure 5.

(a). Preferred posterior–anterior direction (angle 0°). Only the lower coil contributes to the field along this axis. Stimulation occurs at t = 0. (b). Preferred left-right direction (angle 90° = 0.5 π). Only the upper coil contributes to the field along this axis. Stimulation occurs at t = 0.5 π once the lower coil is operated. (c). Preferred direction at angle 0.7 π. Both coils contribute to the field along this axis. Stimulation occurs at about t = 0.6 π once the field reaches the threshold (dashed line).