Figure 3.

Schematic diagram showing the major features of the saccade control circuit. Desired displacement of the eye serves as the reference input to a comparator. An internal estimate of current eye displacement is subtracted from the reference signal to produce a signal of current motor error. This is the input to the saccade burst generator – an exponential function that produces a signal proportional to saccade velocity (burst generator function is displayed: “Vel” is the velocity command as a function of time; G is the asymptotic value of the exponential function or “gain”; ME is the motor error input). The saccade velocity command is the direct input to the “oculomotor plant” (muscles, connective tissue and orbital mechanical properties approximated by a second order linear filter). The second input to the plant is the integral of the velocity command (1/s = Laplace notation for integration). In addition a second resettable integrator resides in the feedback pathway and contributes to the generation of the internal estimate of current displacement.