  As augmented reality technology and hardware become more mature and
affordable, researchers have been exploring more intuitive and discoverable
interaction techniques for immersive environments. In this paper, we
investigate multimodal interaction for 3D object manipulation in a multi-object
virtual environment. To identify the user-defined gestures, we conducted an
elicitation study involving 24 participants for 22 referents with an augmented
reality headset. It yielded 528 proposals and generated a winning gesture set
with 25 gestures after binning and ranking all gesture proposals. We found that
for the same task, the same gesture was preferred for both one and two object
manipulation, although both hands were used in the two object scenario. We
presented the gestures and speech results, and the differences compared to
similar studies in a single object virtual environment. The study also explored
the association between speech expressions and gesture stroke during object
manipulation, which could improve the recognizer efficiency in augmented
reality headsets.
