Pendular optokinetic nystagmus(P-OKN) was studied with the use of a rotating optic cylinder, artificial visual field defects and a rotating chair. The optokinetic stimuli consisted of twelve stripes rotating with a variable velocity (pendular rotation). The pendular rotation was applied at a frequency of 0.1 Hz and a peak velocity of 120 degrees/sec. Artificial visual field defects were made with contact lenses to simulate foveal vision, peripheral vision, and hemianopsia. Rotation of the chair was applied at 2 and 8 degrees/sect at a uniform angular acceleration and a peak angular velocity of 100 and 160 degrees/sec.
1. At the same absolute speed of the optical cylinder, nystagmus was larger in the accelerating phase than in the decelerating phase. The P-OKN field was on the quick phase side during cylinder acceleration and on the slow phase side during cylinder deceleration.
2. Foveal and peripheral vision had the same effect on P-OKN. With foveofugal optokinetic stimulation, P-OKN showed good release in the accelerating phase but poor release in the decelerating phase. With foveo-petal optokinetic stimulation, P-OKN release showed no relationship between acceleration and deceleration. With artificial visual field defects, the P-OKN field was on the quick phase side when visual function was good and shifted to the slow phase side when visual function was reduced.
3. P-OKN was promoted when the head was rotated in the direction opposite to that of optical cylinder rotation. On the other hand, when the head and the optical cylinder both rotated in the same direction, P-OKN was inhibited. With head rotation at 2 degrees/sec2, promotion of P-OKN was stronger than inhibition. On the other hand, promotion was weaker than inhibition at 8 degrees/sec2. The field of optokinetic nystagmus was biased to the quick phase side (promotion) compared with the slow phase side (inhibition).
