Overview
Traditionally, augmented reality (AR) applications have primarily
used head mounted displays (HMDs) for visual output. Most designers
want the AR experience to be a seamless and mode-less
integration between real and virtual worlds. Many argue that this
can best be facilitated using HMDs, which augment the user’s visual
field directly and persistently. No further user-controlled tools
are necessary to visualize the virtual layer. This is particularly useful
for hands-free operation and interaction with dynamic virtual
content.
Recently, there have also been an increasing number of AR applications
that use hand held displays such as ultra-mobile computers,
PDAs, or cell phones as the primary display. The reason most
often cited for using hand held displays is user acceptance. Proponents
of this technology claim that for AR to be broadly adopted in
the short term, it will need to run on devices similar to those that
are already ubiquitous.
Little is known about the relationship between display type and
user performance in AR. In this project, we describe a user study
that examines how display choice affects selection and annotation
in an AR environment. These general tasks can be broken up into
two conceptual parts. First the user must search for and locate the
object they wish to select or annotate, and second they must move
some sort of cursor or selection device to that location. One difference
that sometimes exists between selection and annotation is
that it is often necessary to assign a distance to place an annotation,
as well as a direction vector. In the past, we have looked at techniques
for creating annotations at a distance, including techniques
to determine the distance to the object being annotated, but for
this study we are only concerned with selection or annotation on
the image plane, and assume that there is sufficient world model
information for finding the 3D location of objects using techniques
like ray casting.
This project compares two different tasks, selection and visual
search, among three representative display types. The selection
task tested how easily people would move the display to center it
on target objects. For the search task, we had users look for items
among both real and virtual objects in order to determine if display
choice has different effects based on the amount of virtual content
present in the AR scene. The first display device we used is a head
mounted display, and the second is a hand held display, which we
used in two different configurations. First, users were asked to hold
the hand held display at approximately waist height and look down
at it, like they would do with a tablet computer. The camera was pointed directly
forward. The second configuration involved
holding the hand held display like a magic lens where the camera
is pointing behind the display, with users holding the display up
at head height, and looking “through” it.
In our original study we found several significant results. We found that for
certain annotation and selection tasks, a magic lens may be more
suitable than a HMD. It performed faster for the cursor movement
portion of the study and no worse than the others during the visual
search part of the study. For the visual search portion of our study,
we found it surprising that there was no significant difference in either
the virtual or real case in task performance among the different
displays. In spite of that, users had strong feelings that they had performed
better with particular displays. They favored the hand held
displays that they could look away from when searching for real
objects, and the HMD when searching for virtual objects. These results
suggest to us that there were other factors involved that caused
the task performance to be so similar. Perhaps the user’s high task
attention overwhelmed the smaller differences caused by visual difference
among displays.
Ongoing Work
We are planning a follow up study for this project to further clarify our results.
We hope that including a secondary distraction task will break users focus on then
task, simulating a user who is switching between different tasks within an application.
We also plan to require the users to conduct the visual search task over a largera,
making it necessary for users to move the display device far more than they did
in the original study.
Publications
Jason Wither, Stephen DiVerdi, and Tobias Höllerer
Evaluating Display Types for AR Selection and Annotation
In Proc. International Symposium on Mixed and Augmented Reality, November 2007
(PDF)
(Video)
|