Stiffness Perception With Delayed Visual Feedback During Unimanual and Bimanual Interactions

During interactions with elastic objects, we integrate haptic and visual information to create stiffness perception. In many practical applications, either haptic or visual feedback may be delayed. Previous studies have investigated stiffness perception with delayed force or visual feedback in vertical interactions using the right hand. However, most daily interactions entail bimanual interactions that may be performed horizontally. Here, we studied the effect of visual delay sizes on stiffness perception during horizontal right-hand unimanual and bimanual interactions. We designed two forced-choice paradigm experiments. We asked right-handed participants to interact with pairs of elastic objects with either their right hand or both hands and determine which object felt stiffer. We delayed the visual information of one of the objects. In right-hand unimanual and bimanual interactions, consistent with previous studies, visual delay caused an overestimation of stiffness that increased with delay size. Interestingly, the participants' sensitivity to small differences in stiffness deteriorated due to delay only in right-hand unimanual and not bimanual interactions. The advantage in sensitivity of bimanual interactions compared to right-hand unimanual interactions could be considered in designing visual-haptic interfaces with delayed feedback. However, future studies are needed to determine the sensory mechanism that is responsible for this result.