Generally I think of it in terms of number of frames @ 60 fps. Anything below one frame (16.66ms) and whether or not any sort of real feedback is even received

Generally I think of it in terms of number of frames @ 60 fps. Anything below one frame (16.66ms) and whether or not any sort of real feedback is even received (let alone interpreted by the brain) becomes a probability density function. With each additional frame after that providing more and more kinesthetic friction until you become completely divorced from the feedback around 15-20 frames.