We experience spatial separation and temporal asynchrony between visual and

haptic information in many virtual-reality, augmented-reality, or teleoperation systems.

Three studies were conducted to examine the spatial and temporal characteristic of

multisensory integration. Participants interacted with virtual springs using both visual and

haptic senses, and their perception of stiffness and ability to differentiate stiffness were

measured. The results revealed that a constant visual delay increased the perceived stiffness,

while a variable visual delay made participants depend more on the haptic sensations in

stiffness perception. We also found that participants judged stiffness stiffer when they

interact with virtual springs at faster speeds, and interaction speed was positively correlated

with stiffness overestimation. In addition, it has been found that participants could learn an

association between visual and haptic inputs despite the fact that they were spatially

separated, resulting in the improvement of typing performance. These results show the

limitations of Maximum-Likelihood Estimation model, suggesting that a Bayesian

inference model should be used.