  An increasing number of virtual reality applications require environments
that emulate real-world conditions. These environments often involve dynamic
virtual humans showing realistic behaviors. Understanding user perception and
navigation among these virtual agents is key for designing realistic and
effective environments featuring groups of virtual humans. While collision risk
significantly influences human locomotion in the real world, this risk is
largely absent in virtual settings. This paper studies the impact of the
expected collision feedback on user perception and interaction with virtual
crowds. We examine the effectiveness of commonly used collision feedback
techniques (auditory cues and tactile vibrations) as well as inducing
participants to expect that a physical bump with a real person might occur, as
if some virtual humans actually correspond to real persons embodied into them
and sharing the same physical space. Our results indicate that the expected
collision feedback significantly influences both participant behavior
(encompassing global navigation and local movements) and subjective perceptions
of presence and copresence. Specifically, the introduction of a perceived risk
of actual collision was found to significantly impact global navigation
strategies and increase the sense of presence. Auditory cues had a similar
effect on global navigation and additionally enhanced the sense of copresence.
In contrast, vibrotactile feedback was primarily effective in influencing local
movements.
