State dependence of stimulus-induced variability tuning in macaque MT
Fig 7
Fano factor tuning and heterogeneity both contribute to lower discriminability thresholds in MT populations.
(A) Model population with 20 homogeneous tuning curves. (B) Cramer-Rao bound in homogeneous population models of 200 neurons over time with short-range correlations (cmax = 0.1, 〈c〉 = 0.0438) and information-limiting correlations (ϵ = 4). Tuning curves are fit to the average cumulative response from motion onset up to time T. Black traces show performance of models with varying stimulus-dependent variance. The solid trace is FFTI > 0, the dashed trace is FFTI = 0, and the dotted trace is FFTI < 0. The dashed gray line indicates the stimulus discriminability threshold for smooth pursuit behavior in macaques 125 ms after pursuit initiation. The red trace indicates the bound on discriminability at 2° set by the information-limiting correlations. (C) Same as in (B) but for neuronal populations of different sizes with first-order statistics matched to the average response at time 250 ms after motion onset. (D) Sample population of 20 heterogeneous tuning curves drawn from measured tuning curves in recorded neurons. (E,F) Same as in (B,C) but for heterogeneous populations. The shaded areas show the standard deviation of the Cramer-Rao bound.