shown the buttons should be approximately 9.2 mm
wide for a mobile device: with these dimensions, the
target areas are as small as possible, without decreas-
ing performance. Moreover, as Yang (Yang, ) states,
complex control techniques should be avoided - older
people may find it difficult to perform sliding and re-
volving gestures on touch screen. While evaluating
the use of web-based interfaces by the elderly, Kur-
niawan and Zaphiris (Kurniawan and Zaphiris, 2005)
found that they prefer the presence of graphics if it is
logically associated with the content, and not only for
decorative purposes. Animated elements tend to con-
fuse older users and therefore should be avoided in
general, while animated avatars are considered use-
ful. The icons should be simple and meaningful, and
large enough to be identified by people with impaired
vision (Maguire, 1999). All these studies help us to
create an overall picture about the general rules for de-
signing usable touch screen interfaces, which require
a minimal effort in understanding by older users.
4.2 Behavioural Analysis Through
Environmental Sensors
In the literature there are a multitude of AAL systems
aimed at monitoring the daily activities to support in-
dependent living, evaluating in a natural and continu-
ous way the health and cognitive state, providing au-
tomated assistance, and reducing the pressure on rel-
atives or caregivers. In this context, one of the most
important applications is represented by the fall detec-
tion. As previously mentioned, in fact, falls are one of
the main threats to independent life of the elderly sub-
jects. Several systems have been developed for this
purpose, especially based on computer vision, such as
(Gasparrini et al., 2014), or wearable sensors (Huynh
et al., 2014; Pierleoni et al., 2014). Other solutions
focus, instead, on the individual activity detection,
such as moving (walking, standing, etc.), as shown
in (De Santis et al., 2014). In (Zhang et al., 2013) a
platform, called ENLIVEN,using environmental non-
intrusive sensors, has been presented: the system is
able to understand activities and vital signs, and, us-
ing such data, to make decisions. Algorithms based
on fuzzy logic have been used in (Medjahed et al.,
2009) for the recognition of different activities, such
as Sleeping, Getting up, Toileting, etc. In this case,
the monitoring system uses three main subsystems:
two microphones to monitor the sound, a wearable de-
vice that measures physiological data, a set of infrared
sensors for detection of the presence and posture of
the subject. Even in (Fleury et al., 2010), the mon-
itoring system consists of presence sensors (IR), mi-
crophones for the sound and speech recognition and
a wearable sensor; contacts on doors and refrigerator,
temperature sensors and humidity are also added. The
technique used for the activity classification exploits
the Support Vector Machines (SVMs). The method
presented in (Nam et al., 2011), based on (Kim et al.,
2009), allows to obtain, instead, data such as time of
occurrence, probability of occurrence, daily time in-
tervals and the relations between the various activity
sets, shown according to a specific graphical model.
Algorithms that can distinguish patterns of activity
occurring frequently, through the analysis of the tem-
poral relations in a multi-user environment, have been
described in (Jakkula et al., 2007). These algorithms
have been used in the context of the CASAS project
(Rashidi and Cook, 2009), a smart environment pro-
viding a non-invasive assistive tool for dementia pa-
tients at home.
5 METHODOLOGY
The following section describes the platform adopted,
the design choices and the methodologies used in the
development phase. A brief overview on the AAL
platform underlying the project is presented first, then
the user interface based on touch screen technology is
explained in detail, paying close attention to the de-
sign choices. Finally, algorithms for the presence and
activity recognition are exposed.
5.1 Context: A Smart Home in AAL
Before discussing the design methodologies used, a
quick overview of the underlying AAL framework
will be provided. Such a framework covers several
aspects of the home living, such as independent liv-
ing, home security, health monitoring and environ-
mental control. From a general point of view, in the
system architecture the information is generated by a
multiplicity of subsystems. They implement specific
functionalities and, through well defined policies and
rules, send the data to a local server (some specific
information are delivered remotely), which correlates
all the received data, collects information on the status
of the system and on the user’s habits and behaviour
(see Fig 1).
The system is able to:
• analyse behavioural data in a unobtrusive way on
the long term in order to make a preliminary diag-
nosis compared to the observed changes in habits;
• allow the user to interact with the home environ-
ment, facilitating certain tasks, such as opening or
closing windows and blinds, and turning on or off
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