Fig. 5.

Ratio of the amplitudes of measured hemoglobin concentration oscillations at the cardiac frequency for subject no. 1 for all channels. Since $\mathbf{O}$ and $\mathbf{D}$ are not in phase, it follows that $|\mathbf{O}|/|\mathbf{T}|$ (black circles) does not equal $|\mathbf{O}|/(|\mathbf{O}|+|\mathbf{D}|)$ (gray squares).