  Early visual to auditory substitution devices encode 2D monocular images into
sounds while more recent devices use distance information from 3D sensors. This
study assesses whether the addition of sound-encoded distance in recent systems
helps to convey the "where" information. This is important to the design of new
sensory substitution devices. We conducted experiments for object localization
and navigation tasks with a handheld visual to audio substitution system. It
comprises 2D and 3D modes. Both encode in real-time the position of objects in
images captured by a camera. The 3D mode encodes in addition the distance
between the system and the object. Experiments have been conducted with 16
blindfolded sighted participants. For the localization, participants were
quicker to understand the scene with the 3D mode that encodes distances. On the
other hand, with the 2D only mode, they were able to compensate for the lack of
distance encoding after a small training. For the navigation, participants were
as good with the 2D only mode than with the 3D mode encoding distance.
