Fig. 13.

Least square fits of g by the sigmoid function of Equation 4 (same preparation as in Fig.12B). A, Static nonlinearity g at four values of l/‖v‖ determined following the procedure outlined in Fig. 12A. For each panel thesolid line is the mean value of g , and thedotted line represents 1 SD from the mean. The dashed line is the best least square fit with the sigmoid function of Equation 4 (Materials and Methods). B, Fits of the time course of DCMD firing rate during object approach using Equation 11 and the function g determined in A. In each panel thesolid line is the time course of the firing rate during object approach (mean over 10 trials), the dotted line is the time course of the kinematic variable z(t) (see Eq. 12), and the dashed line is the fit with g, α, and δ determined as explained in Results. Note that in thebottom panel the fit is good up to the time point indicated by the arrow: for larger values of t, z(t) is identically equal to zero, and the time course of the firing rate falls outside the range of validity of Equation 11. A failure to fit the entire time course of LGMD and DCMD firing rate was observed in all of our 15 neurons at values of l/‖v‖ = 5 and 10 msec (see Discussion).