Superposition of the deformations evoked by motoneurons innervating the same class of muscle fibers.A, Optical flow after longitudinal motoneuron L stimulation with a current pulse lasting 5 sec and evoking a spike discharge of ∼14 Hz. B, Optical flow after longitudinal motoneuron 5 stimulation with a current pulse lasting 5 sec and evoking a spike discharge of ∼34 Hz. C,Optical flow after identical simultaneous stimulations of both longitudinal motoneurons. D, Sum of the optical flows shown in A and B (red) compared with the optical flow shown in C(black). E, Elementary deformations of the optical flows shown in A and B (L,gray bars; 5, white bars).F, Sum of the elementary deformations of motoneurons L and 5 (red bars) compared with the elementary deformations of the optical flow shown in C(gray bars). The width of the annuli inA–D is ∼0.8 mm. Equal normalization inE and F.