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in the 3D space; zooming in/out enables better
focus of the data, and cropping enables users to
cut off and look inside the image, for example,
two or three vertebrae from a human spine. With
little tweaking, these techniques could equally be
applied to both learning games and rehabilitation
games. In terms of learning, they could be used
to stimulate hand-eye coordination, which can be
a problem for people with certain visual impair-
ments, as well as to strengthen the muscles in the
hand, wrist, and forearm, which invariably will
atrophy while the patient is wearing a cast while
healing a bone fracture.
Several innovative uses of gestures have been
proposed for interaction with small mobile devices
such as mobile phones and MP3 players. Hudson
and his colleagues (2010), for example, report a
study involving a category of what they refer to as
'inexact and inattentive interactions'. With their
'Whack Gestures' technique, common interactions
are handled with gross motor movements such as
firmly striking the device with an open palm or
heel of the hand moving towards the waist, where
the device is worn at the waist, for example, in a
holder attached to a belt. The authors attempt to
overcome the important problem of accidental
activation of the device by unintended jostling
or bumping that can lead to false positives, by
requiring the user to perform a sequence of sev-
eral movements to signal intended activation of
the device. At present, the whack vocabulary is
quite limited. However, rather than focusing on
the ease of learning the vocabulary and carrying
out the correct movements associated with these,
as would be the typical HCI approach to forma-
tive testing of early prototypes, the preliminary
user-based study aimed to assess the effectiveness
of the proof-of-concept implementation. The
11 participants were shown how to attach the
device correctly before going about their normal
routine while wearing the device for two hours
each, yielding data for 22 hours of use. Thus,
there were no set tasks, no questions to answer,
and no routes or procedures to follow. The data
analysis focused on identifying the frequency of
occurrence of false positives of which they found
only one per 12 hours of this in-the-wild usage,
assessed on six of the 11 participants. No false
positives were found among the remaining five
participants. In addition, the recognizers correctly
classified 100% of the known framing gestures.
The short sequences of gestures are easy to learn,
and, to the extent that these early results may be
indicative of the system's performance, the ac-
curacy levels appear to be impressive.
Relying on rather finer movements, the 'Ges-
ture Watch' (Kim, He, et al., 2007; Lee & Starner,
2009), a wrist-mounted mobile gesture interface
worn on the non-dominant hand, allows non-
contact hand gestures above the wrist to control
mobile devices. Much in the same fashion as the
Whack Gestures technology, the Gesture Watch
requires the user to perform three interactive
movements to avoid accidental activation. First,
the sensors must be triggered, then the command
gesture must be performed, and finally, the sensors
must be de-activated. As in the Whack Gestures
study, the results of a small pilot study are reported.
It included a sample of four participants testing
multiple tactile patterns in two sessions. Data from
a total of 384 trials were thus collected. The level
of performance accuracy was 85.98% in the first,
and 89.45% in the second session. Given the high
accuracy rates for both the Whack Gestures and
the Watch Gesture devices, one may speculate that
the range of movements (commands/vocabulary)
could quite readily be increased. So, the Whack
Gestures could perhaps be employed in situations
in which movement is unrestricted but hands/
fingers or eyes are 'busy/unavailable'. Similarly,
the Gesture Watch could be used in situations
that are unsuitable for wearing a mobile device
on a belt. First responders to a large disaster, for
example, typically wear heavy suits, gas masks
or Head-Up Displays (HUDs), making it difficult
or impossible to handle a device requiring fine
movements. Both technologies could be explored
in that context.
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