Haptic interface technologies for virtual reality applications have been developed to increase the reality and manipulability of a virtual object by creating a diverse tactile sensation. Most evaluation of the haptic technologies, however, have been limited to the haptic perception of the tactile stimuli via static virtual objects. Noting this, we investigated the effect of lateral cutaneous feedback, along with kinesthetic feedback on the perception of virtual object weight during manipulation. We modeled the physical interaction between a participant's finger avatars and virtual objects. The haptic stimuli were rendered with custom-built haptic feedback systems that can provide kinesthetic and lateral cutaneous feedback to the participant. We conducted two virtual object manipulation experiments, 1. a virtual object manipulation with one finger, and 2. the pull-out and lift-up of a virtual object grasped with a precision grip. The results of Experiment 1 indicate that the participants felt the virtual object rendered with lateral cutaneous feedback significantly heavier than with only kinesthetic feedback (p < 0.05 for m ref = 100 and 200 g). Similarly, the participants of Experiment 2 felt the virtual objects significantly heavier when lateral cutaneous feedback was available (p < 0.05 for m ref = 100, 200, and 300 g). Therefore, the additional lateral cutaneous feedback to the force feedback led the participants to feel the virtual object heavier than without the cutaneous feedback. The results also indicate that the contact force applied to a virtual object during manipulation can be a function of the perceived object weight (p = 0.005 for Experiment 1 and p = 0.02 for Experiment 2).

We investigate how different types of haptic feedback to hand affect the perceived size of a virtual object. Multiple haptic interfaces are designed to deliver different types of haptic feedback to hand. In the preliminary experiment, we investigated the effect of cutaneous feedback on the perceived size of the virtual object. The experimental results indicate that the availability of cutaneous feedback resulted in an insignificant effect on the perceived size of the virtual object. On the other hand, the availability of cutaneous feedback led the participants to exert significantly smaller grip force than when there is only force feedback. In the main experiment, we provided haptic feedback to the dorsum of the hand to modulate the hand kinesthesia at the moment of contact with the virtual object. For the reference stimuli, skin-stretch or vibrotactile feedback was provided to a participant's hand along with cutaneous and force feedback to the fingertips. Reference stimuli were rendered only with cutaneous and force feedback to the fingers. The experimental results indicate a significant effect of the type of haptic feedback to the dorsum of a hand. The skin-stretch feedback led the participants to feel virtual objects with a size of 40 mm, larger than without the feedback. The vibrotactile feedback resulted in the perceived size of virtual objects with a size of 20 or 40 mm, smaller than without the vibrotactile feedback.INDEX TERMS Haptic interface, pinch grip, virtual reality, size perception, feedback control. II. GENERAL METHODS A. APPARATUS

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Most of the previous haptic interfaces provides tactile feedback directly to the hand, which can impede the operability. Noting the issue, we propose a haptic system that can provide 3D vector information with continuous skin-stretch feedback. We designed the system to render a 3D vector by combining two orthogonally located continuous skin-stretch modules whose orientation could be controlled. To optimize the stimuli, we conducted a psychophysical experiment that measured human sensitivity to the orientation of the continuous skin-stretch feedback. Considering the asymmetry of tactile sensitivity, we collected the data at two locations of the forearm. The results indicate that the participants were more sensitive to the angle change when the skin-stretch feedback was aligned in the proximal-distal direction. Based on the information, we built an algorithm to set the rotation angle of the skin-stretch module to render any target 3D vector. We conducted two experiments for virtual interaction to evaluate our proposed method. In Experiment 1, we tested if adjusting the skin-stretch orientation could improve the human perception of the virtual surface features, and the result indicated a significant improvement in the surface feature perception with the orientation adjustment. Experiment 2 tested a participant's ability to follow a random 3D contour under two conditions, visual cue (V) condition, and visual and continuous skin-stretch (V+CF) cues condition. For the V+CF condition, the skin-stretch interface rendered the error 3D vector to the participant's forearm. The result indicated a significantly lower root-mean-square error for the V+CF condition than the V condition. Thus, the addition of the continuous skin-stretch feedback benefitted the participants to stay closer to the target virtual contour than with visual information only.

The original version of this Article contained errors in the Abstract."Haptic interface technologies for virtual reality applica have been developed to increase the reality and manipulability of a virtual object by creating a diverse tactile sensation. " now reads:"Haptic interface technologies for virtual reality applications have been developed to increase the reality and manipulability of a virtual object by creating a diverse tactile sensation. ""The results also indicate that the contact force applied to a virtual object during manipulation can be a function of the perceived object weight p = 0.005 for Experiment 1 and p = 0.2 for Experiment 2. " now reads:"The results also indicate that the contact force applied to a virtual object during manipulation can be a function of the perceived object weight (p = 0.005 for Experiment 1 and p = 0.02 for Experiment 2). "These errors have now been corrected in the PDF and HTML versions of the Article.