Labyrinthine and extra-labyrinthine effects on ocular counter-rolling

Ocular torsion was measured in alert monkeys. There was about 5'7' of compensatory ocular counter-rolling (CR) when the head and body were tilted 45' to the right or to the left. CR was the same whether the head or head and body were tilted, and was not much different in the presence or absence of vision. One monkey was tested after serial destruction of the labyrinths. Counterclockwise CR was reduced after left labyrinthectomy and clockwise CR after right labyrinthectomy. That is, each labyrinth appeared to exert the strongest effect on CR to the opposite side. After bilateral labyrinthectomy small but definite amounts of CR were induced by head or by head and body tilt. This has been designated as residual CR. In the intact animal CR is mainly induced by the labyrinths. In the absence of the labyrinths, however, other types of sensory activity can influence the steady angle of torsion of the eyes.