Figure 4.

Temporal evolution of the band-limited electrical activity from a demodulation procedure. (a) The magnitude and phase of the optical response centered at 18 Hz as a function of time, beginning with the onset of the loom. We plotted the demodulate, Ṽ_f(x, y, t), as a sequence of false-colored images with the magnitude of the demodulate coded by the saturation level and the phase of the demodulate coded by the hue; a single normalization is used for the entire sequence. Note the presence of approximately linear (∗ and ∗∗∗) and circular (∗∗) phase shifts. Each frame corresponds to an independent sample (9 Hz); a phase shift of 2π radians corresponds to a cycling through the chromatic scale (e.g., red → green → blue → red). The final row includes contour maps of the phase only at times t = 0.68 s (∗), t = 1.45 s (∗∗), and t = 2.22 s (∗∗∗); each contour corresponds to π/12 radians. Orientation of the optical field is as in Fig. 1a. (b) The magnitude and phase of the demodulate centered at f = 8, 10, 13, 18, and 23 Hz, filtered at W = f/4 (2WT = 2; K = 1), and averaged over a period of four cycles. The center time of the interval was t = 1.51 s (∗∗ in a).