Biomedical Engineering Reference
In-Depth Information
Fig. 17.12
A user interacts with floor-based interface widgets implemented using the interface
design toolkit described in the text
the vibrotactile actuators, in the form of click-like transient vibrations or sliding
frictional vibrations.
A software layer and network protocol is used to facilitate the design of interactive
applications using these techniques. It abstracts the hardware systems, which are
accessed over a local Ethernet network, connects them to the user interface, and
allows an interface designer to instantiate an array of standard user interface controls,
such as sliders, buttons, or toggle switches.
The software processes the sensor data to extract foot-floor contact points that
are used for interaction, provides them with unique IDs that persist while contact is
sustained, and allows to remotely cue localized vibrotactile feedback. Figure
17.12
illustrates a virtual floor-based touch interface.
17.4.4 Usability of Foot-Floor Touch-Surface Interfaces
The authors investigated users' abilities to select on-screen virtual buttons of different
sizes presented at different distances and directions using the floor tile interface
described in the preceding section [
39
]. In this task, the limited resolution of the
force sensors (Fig.
17.7
) was one factor that could influence performance. Users
could activate a button by pressing it within the area of the button with a force
exceeding a threshold of about 35N. Round, virtual buttons ranging in diameter
from 4.5 to 16.5 cm, and presented at four distances, on lines radiating at two angles
from between their feet. Upon selection, the buttons provided visual feedback in
the form of a 20 cm white disc centered in place of the original graphic. Results are
summarized in Fig.
17.13
. Users were found to have selected larger targets within the
allotted two-second interval at a significantly higher rate of success than smaller ones.
Performance with the largest was very high (98 %), and that for the smallest was low
(44 %). Small targets can pose difficulties due to their tendency to be occluded by
the foot during selection, which is mitigated during top-down projection, since they
are projected on top of the foot, and can be more affected by limitations arising from
factors such as shoe width, human motor abilities, and sensor positioning errors.
