The use of haptic devices in Virtual Reality applications makes the interaction with the digital objects easier, by involving the sense of touch in the simulation. The most widespread devices are stylus-based, so the user interacts with the virtual world via either a tool or a stylus. These kinds of devices have been effectively used in several virtual prototyping applications, in order to allow the users to easily interact with the digital model of a product. Among the several open issues related to these applications, there is the choice of the set-up and of the techniques adopted to combine the visual and the haptic stimuli. This paper presents the comparison of three different solutions specifically studied for virtual prototyping applications and in particular for usability assessment. The first is a simple desktop configuration where the user looks at a screen, and visual and haptic stimuli are presented in a de-located manner. The second is a HMD based set-up where the user has a more natural first-person immersive interaction. The third requires a video-see-trough HMD in order to augment the virtual scene with the visualization of the real user’s hand. The test realized with the users on these three different setups have been finalized to study the effect of two different factors that are crucial for the effectiveness and the user-friendliness of the interaction. One is the perception of the visual and haptic stimuli in a collocated manner; the other is the visualization of his/her own hand during the interaction with the virtual product.
