Fig. 3.

Correction for hemodynamic signals. A–C: Fourier phase maps in response to a 5-s on, 5-s off binary noise stimulus (as in Fig. 2), showing significant vascular artifact present in green (A) and blue (B) illumination but greatly reduced in the subtraction (C). Scale bar, 1 mm. D–F: time course of signals for point shown by circles in A–C, demonstrating that blue − green subtraction eliminates a delayed, slow dip, evident in the green reflectance signal. Stimulus duration is shown in gray.