The time intervals for display of shapes are illustrated. Fig. 1a shows the duration of emission from any given LED, designated as T1, this being 0.1 ms. Fig. 1b specifies that the onset-to-onset interval of successive pulses within a given subset, designated as T2, which was also 0.1 ms. In Fig. 1c the pulses are illustrated as a string of beads. The four addresses of each subset are displayed as a group, separated by the T3 interval. For display of a given shape, theT3 interval was 1, 3, 9 or 27 ms.