  Mid-air haptic interfaces have several advantages - the haptic information is
delivered directly to the user, in a manner that is unobtrusive to the
immediate environment. They operate at a distance, thus easier to discover;
they are more hygienic and allow interaction in 3D. We validate, for the first
time, in a preliminary study with sighted and a user study with blind
participants, the use of mid-air haptics for conveying Braille. We tested three
haptic stimulation methods, where the haptic feedback was either: a) aligned
temporally, with haptic stimulation points presented simultaneously (Constant);
b) not aligned temporally, presenting each point independently
(Point-By-Point); or c) a combination of the previous methodologies, where
feedback was presented Row-by-Row. The results show that mid-air haptics is a
viable technology for presenting Braille characters, and the highest average
accuracy (94% in the preliminary and 88% in the user study) was achieved with
the Point-by-Point method.
