Abstract: In this research 30 military university students each experienced a series of optokinetic step stimulation(5 , 10,15,20,30,40,60,80,100,120deg/sec)under two different instructions, Each stimulus continued for 20 seconds. The optokinetic nystagmus was recorded with tape recorder, at the same time, the latency and fuzzy estimate magnitude of the illusion were recorded. The nystagmus was analysed with a computer analysis system of ENG,the magnitude of illusion was measured with a fuzzy set model to estimate the magnitude of vestibular sensation.The main results are as follows:1.The SV, FV, SA, FA of Optokinetic nystagmus incresed with optokinetic speed, between 60-120/s, after that they stayed constant,but the ST and FT were different by decresing with stimulus speed, the lowest point was at 60/s, then incresing slowly.2. Between 5-120/s,the magnitude of optokinetic illuision incresed with stimulus speed lineally.3.There was no cause and result between OKN and optokinetic illusion. OKN does not elict optokinetic illusion, and optokinetic illusion does not produce OKN.Under low stimulus velocity,the fuzzy magnitude of the illusion increased significantly while the OKN was refrained. Indicating that OKN reduced the optokinetic illusion.

Key words: optokinetic stimulus, optokinetic nystagmus, optokinetic illusion