FIG. 4.

The VAR is maintained during passive head rotation. A: movements of the head (black), left ear (blue), ear-on-head (red), gaze (green), and the platform supporting the cat (dashed black) during a trial in which an acoustic target was turned on at −447 ms (red vertical arrow) and remains on for 1,000 ms at −40° (black horizontal arrow on the right axis). All traces are synchronized to the onset time of the motor that rotates the platform in the horizontal plane, in this case to the left. The small green arrow points to a small ear saccade to the left in response to the noise of the motor coming on. B: velocity traces for the head (black), ear-on-head (red), and eye-on-head (green) for the same movements in a. The leftward head movement evokes a compensatory rightward ear movement that keeps the ear roughly stable in space and shows the passive VAR (shaded). The phase of passive VAR is denoted by the shaded areas under the ear-on-head trace and by the double-headed arrow and has a gain = 45.2/−61.9 = −0.73. C and D: another trial with platform movement in the opposite direction. Same format as in A and B. The head, gaze, and ears are near 0° when the target at −30° came on so orientation to the leftward target evokes an active VAR (left shaded region) as well as a passive VAR (right shaded). Small vertical tick marks indicate the peak ear-on-head and peak head velocity values used to estimate the active VAR gain (213.9/−184 deg/s = −1.16; at −267 and −285 ms, respectively). The passive VAR gain (−39.0/39.0) = −1.0.