Figure 3.

The magnitude and phase of the spatial coherence of the optical signal from a space–frequency SVD analysis (Methods). (a) The coherence averaged over a T = 3 s interval both prior to and subsequent to the onset of stimulation. In the latter case the interval encompassed the entire epoch of significant spectral power in the band at 18 Hz (Fig. 2a). The coherence was estimated at successive frequency bins (2WT = 3.0; K = 7); a value of C(f) ≅ 0.14 indicates the lack of significant coherence. (b) Phase (contour lines) and amplitude (false color) of the coherence at f = 3 Hz prior to stimulation. The image formed by the magnitude of Ṽ₁(x, y, f = 3) defines the spatial distribution of coherence, and the phase of Ṽ₁(x, y, 3) defines the temporal delays between different regions. The relative magnitude is false colored with red for maximum and blue/green for zero, and the phase is overlaid as a contour plot with π/12 radians per contour. The arrow indicates the dominant direction of the gradient. (c–f) Phase and amplitude at f = 3, 8, 18, and 22 Hz, respectively, during stimulation by a loom. (g) Phase and amplitude at 18 Hz for the next trial with the same animal. Orientation of the optical field is as in Fig. 1a.