The theoretical development, above, resulting in Eq. (7) for the two-dimensional case and Eq. (12) for the 1-D case, along with the experimental findings, lends credence to the choice of a Voigt model. From these equations, it becomes apparent that this model selection is not binary, but is actually points along a continuum, with the Lorentzian and Gaussian models serving only as the outer limits to the continuum. Inspection of Eq. (12) reveals that LSCI is sensitive to both diffusive flux, and advective flux, , where the total flux, . If the particle motion is assumed to be entirely random (Brownian), then LSCI is revealing and the Lorentzian model should be adopted. Alternatively, if the particle motion is assumed to be entirely ordered, then LSCI is revealing and the Gaussian model should be adopted. However, in most normal cases of interest both components of total flux will be present and the appropriate statistical model is some combination between the Lorentzian and Gaussian models. As suggested above, one solution to this is to employ a Voigt model,8 which is the convolution of the Lorentzian and Gaussian models, or some other weighted linear combination of the two, where the weights reflect the relative contributions of diffusive flux and advective flux. Readers are referred to Duncan and Kirkpatrick8 for more details on this model. When viewed in terms of mass transport, then, it becomes apparent that the oft cited binary decision between the Lorentzian and Gaussian models is a false decision and that these two models are simply limiting behaviors governed by the diffusion with drift equation. 9 As noted in Sec. 2, a clear relationship between flux, flow model, speckle contrast, and decorrelation time of the speckle has not yet been fully developed and presented in the literature. Some authors, notably Kazmi et al.13 have made some progress in this area, however.