OTOLITH ORIENTATION AND DOWNBEAT NYSTAGMUS IN THE NORMAL CAT

Upward drift of the eyes in darkness, influenced by whole body orienta tion, was studied in 12 cats using electromagnetic search coil and ele ctro-oculographic techniques. Animals were positioned stationary with respect to gravity with 0 degrees tilt (''upright'') or rolled 90 degr ees (''on side''), pitched 90 degrees (''on nose'' or ''on tail''), or inverted 180 degrees (''upside down''). A downbeat quick-phase nystag mus (slow-phase upward in the cat's orbit) was measured, varying in ma gnitude with angle of tilt (0.21 degrees/s at 0 degrees tilt, 4.14 deg rees/s at 180 degrees tilt). The drift was not present in the light. U pward eye velocities over a range of body orientations in darkness sug gest a systematic drive to the eyes which increases with tilt away fro m upright, The relationship of this behavior to previous models of ang ular velocity estimation by an otolith-driven central mechanism is dis cussed.