Optical see-through head-mounted displays (OST HMDs) are becoming increasingly popular as they get better and smaller. One application area is interaction with virtual content, which is more intuitive when using physical objects as tangibles. Since it is not possible to use a matching replica for each virtual object, it is necessary to identify physical objects that can represent several different virtual objects. As a first step, we investigated to what extent a physical object can differ in size from its virtual counterpart.Since the perception of content in optical see-through Augmented Reality (OST AR) is strongly influenced by the ambient lighting, the illumination intensity was considered in our study. We investigated three indoor lighting conditions and their effects on the perception of seven different size variations between the physical object and its virtual overlay.The results of the study show that there is a decrease in usability and presence with increasing illuminance. However, this cannot be avoided when applications are run under realistic interior lighting conditions. Furthermore, the results demonstrate that the size ranges in which a physical object can deviate from its virtual counterpart without having a strong negative impact on usability, presence and performance increase with increasing environmental illumination. Therefore, it is possible to interact with even smaller and even larger physical props to manipulate the associated virtual content under brighter lighting conditions.

Optical see-through AR headsets are becoming increasingly attractive for many applications. Interaction with the virtual content is usually achieved via hand gestures or with controllers. A more seamless interaction between the real and virtual world can be achieved by using tangible objects to manipulate the virtual content. Instead of interacting with detailed physical replicas, working with abstractions allows a single physical object to represent a variety of virtual objects. These abstractions would differ from their virtual representations in shape, size, texture and material. This paper investigates for the first time in optical see-through AR whether size variations are possible without major losses in performance, usability and immersion. The conducted study shows that size can be varied within a limited range without significantly affecting task completion times as well as feelings of disturbance and presence. Stronger size deviations are possible for physical objects smaller than the virtual object than for larger physical objects.