Figure 1

Periodic patterns under a pulse-train signal. (a) In the presence of a square-wave field, a vertical alignment cell exhibited a random texture with umbilical defects owing to the absence of an easy axis. (b) In contrast, in response to a train of pulses (10 V and 20 Hz), a blinking periodic pattern appeared. When the crossed polarizers were rotated (arrows), dark areas became bright and vice versa (inset).