Figure 3. Performance of Model Before, During and After Training with an Undelayed Retinal-Slip Signal.

The plant P is first-order filter with time constant 0.1 s, and the brainstem controller B has an undergained (50%) direct pathway and a leaky integrator (TC = 1 s) in the indirect pathway (details in Methods).

(A) Eye-position response to sudden head displacement. The desired and post-training performances are effectively identical, so that only the latter is shown.

(B) System gain for sinusoidal input signals as a function of frequency (Bode gain plot). Gain is measured as ratio of eye velocity amplitude to head velocity amplitude. Performance before training is shown both for the complete brainstem controller (“pre”), and for the brainstem controller as simple gain (“B = 0.5”), which corresponds to the direct pathway on its own. After training, the desired and post-training performances overlap and only the latter is shown.

(C) Decline in retinal-slip amplitude with training. Root-mean-square (RMS) retinal-slip amplitudes, measured over a 5 s training batch, plotted against number of training batches.

(D) Example of retinal-slip to mixed-frequency head-velocity input before and after training.