Figure 11. Spatiotemporal summation of protraction angles in response to stimulation of two adjacent intrinsic muscles. A, Scheme of the biomechanical model. The middle follicle is innervated by two intrinsic muscles, the anterior (red) and the posterior (black). The arrows indicate stimuli to the posterior and anterior muscles (denoted by “Stim Post” and “Stim Ant,” respectively). B, Maximal amplitudes of protraction angles of the middle whisker as functions of the muscle force scaling factor, A, in response to the innervations of the posterior (θpost,musclemax, black), anterior (θant,musclemax, red), or both (θpost+ant,musclemax, green) muscles. The maximum value of the linear sum of the separate responses to each muscle is also plotted ((θpost,muscle(t) + θant,muscle(t)), blue). The whisker resting angle is θ0 = 70° and the two muscles are stimulated simultaneously (Δt = 0). C, The maximal amplitudes of protraction angles described in B as functions of Δt for θ0 = 70°, A = 10. Lines are as in B. D, The “spatiotemporal linearity index” [S(A, Δt), Eq. 16] for A = 10 as a function of θ0 and Δt. Inset, S(A, 0) as a function of θ0 for A = 10. E, F, Peak amplitudes of whisker protraction angles, θposteriorpeak (black), θmiddlepeak (blue), and θanteriorpeak (red), as functions of θ0. Parameters, A = 1.33 (E, same as in Fig. 6F) and A = 10 (F); Δt = 0. Note that the θpeak values of the posterior and anterior whiskers among the three (black and red lines) when A is small (F) are equal to the θpeak values of the posterior and anterior whiskers in Figure 6F, where they are adjacent.