General architecture of the model. This figure represents the different parts of the model and their feedforward and feedback connections. First, a target (T) appears on the retina and generates a position error (PE) sent to the cortex. Second, the cortex computes the desired eye displacement (Δ E) and sends it to the superior colliculus (SC) and the cerebellum (CBLM). Third, SC and CBLM send a drive to the brainstem which sends back an efference copy of the eye position to CBLM which controls eye displacement. CBLM also modulates the collicular activity through a facilitation signal. Finally, the brainstem sends a drive to the eye plant. Lines with arrowheads correspond to excitation, with filled circles correspond to inhibition, and with filled diamonds correspond to facilitation. Details of the brainstem connectivity are presented in Figure 2.