  Screen-based Augmented Reality (AR) systems can be built as a window into the
real world as often done in mobile AR applications or using the Magic Mirror
metaphor, where users can see themselves with augmented graphics on a large
display. Such Magic Mirror systems have been used in digital clothing
environments to create virtual dressing rooms, to teach human anatomy, and for
collaborative design tasks. The term Magic Mirror implies that the display
shows the users enantiomorph, i.e. the mirror image, such that the system
mimics a real-world physical mirror. However, the question arises whether one
should design a traditional mirror, or instead display the true mirror image by
means of a non-reversing mirror? This is an intriguing perceptual question, as
the image one observes in a mirror is not a real view, as it would be seen by
an external observer, but a reflection, i.e. a front-to-back reversed image. In
this paper, we discuss the perceptual differences between these two mirror
visualization concepts and present a first comparative study in the context of
Magic Mirror anatomy teaching. We investigate the ability of users to identify
the correct placement of virtual anatomical structures in our screen-based AR
system for two conditions: a regular mirror and a non-reversing mirror setup.
The results of our study indicate that the latter is more suitable for
applications where previously acquired domain-specific knowledge plays an
important role. The lessons learned open up new research directions in the
fields of user interfaces and interaction in non-reversing mirror environments
and could impact the implementation of general screen-based AR systems in other
domains.
