  The release of Microsoft's HoloLens headset addresses new types of issues
that would have been difficult to design without such a hardware. This
semi-transparent visor headset allows the user who wears it to view the
projection of 3D virtual objects placed in its real environment. The user can
also interact with these 3D objects, which can interact with each other. The
framework of this new technology is called mixed reality. We had the
opportunity to numerically transform a conventional human nutrition workshop
for patients waiting for bariatric surgery by developing a software called
HOLO_NUTRI using the HoloLens headset. Unlike our experience of user and
conventional programmer specialized in the development of interactive 3D
graphics applications, we realized that such a mixed reality experience
required specific programming concepts quite different from those of
conventional software or those of virtual reality applications, but above all
required a thorough reflection about communication for users. In this article,
we propose to explain our design of communication (graphic supports, tutorials
of use of material, explanatory videos), a step which was crucial for the good
progress of our project. The software was used by thirty patients from Le
Puy-en-Velay Hospital during 10 sessions of one hour and a half during which
patients had to take in hand the headset and software HOLO_NUTRI. We also
proposed a series of questions to patients to have an assessment of both the
adequacy and the importance of this communication approach for such experience.
As the mixed reality technology is very recent but the number of applications
based on it significantly increases, the reflection on the implementation of
the elements of communication described in this article (videos, exercise of
learning for the use of the headset, communication leaflet, etc.) can help
developers of such applications.
