Figure 2. Linearised Model of Horizontal Vestibulo-Ocular Reflex, Derived from the Neural Circuitry Illustrated in Figure 1 .

(A) Head velocity x(t) is processed by the filter V, then added to the output z(t) of the adaptive filter C (which corresponds to the floccular region of cerebellum). The summed signal is then passed to the brainstem controller B. The output of B is a motor command y(t), which acts on the plant P. A copy of y(t) is sent back to the adaptive filter C. The command y(t) acts on P to move the eyes, a movement which is added to the head velocity x(t): net image movement is detected as retinal slip e(t) and sent to C.

(B) Structure of the adaptive filter shown as C in (A). The copy of the eye-movement command y(t) arrives as mossy fiber input, and is decomposed into components y₁(t) .... y_n(t) by the granule cell layer. Each output component y_i(t) is weighted by w_i, corresponding to the efficacy of the corresponding synapse between a parallel fiber and the Purkinje cell. The weighted components are summed by the Purkinje cell and constitute the filter output. The value of each weight w_i is adjusted according to the current value of the correlation between its component y_i(t) and the global retinal slip signal e(t), which arrives as climbing fiber input.