Implicit Human Computer Interaction Through Context

Implicit Human Computer Interaction Through Context
Albrecht Schmidt
Telecooperation Office (TecO), University of Karlsruhe
Vincenz-Prießnitz-Str. 1, 76131 Karlsruhe
Germany
albrecht@teco.edu
www.teco.edu
Abstract
(ranging form simple temperature sensors to
In this paper the term implicit human computer
cameras), and the resulting perceptional
interaction is defined. It is discussed how the
capabilities as well as the fact that the main user
availability of processing power and advanced
group of current computing devices (e.g. mobile
sensing technology can enable a shift in HCI
phones, PDAs, etc.) are non experts, we may
from explicit interaction, such as direct
observe yet another shift in HCI. Devices that
manipulation GUIs, towards a more implicit
have perceptional capabilities (even if they are
interaction based on situational context. In the
very limited) will start the shift from explicit HCI
paper an algorithm that is based on a number of
towards a more implicit interaction with
questions to identify applications that can
machines.
facilitate implicit interaction is given. An XML-
A vision of future devices

based language to describe implicit HCI is
We will be able to create (mobile) devices that
proposed. The language uses contextual variables
can see, hear and feel. Based on their perception,
that can be grouped using different types of
these devices will be able to act and react
semantics as well as actions that are called by
according to the situational context in which they
triggers. The term of perception is discussed and
are used.
four basic approaches are identified that are
In this paper it will be shown that this vision is
useful when building context-aware applications.
not as far ahead as it seems. In our research we
Providing two examples, a wearable context
start with the perception of simple concepts and
awareness component and a sensor-board, it is
with their exploitation. Providing a number of
shown how sensor-based perception can be
examples and demonstrators it is discussed how
implemented. It is also discussed how situational
basic perception could enable a shift from explicit
context can be exploited to improve input and
towards implicit HCI.
output of mobile devices.

2 Implicit
Interaction
Keywords: context awareness, context sensing,
Observing communication between humans we
implicit human computer interaction, perception,
can see that a lot of information is only
ubiquitous computing.
exchanged implicitly. The way people interact
with each other and also the situation in which
1 Introduction
they interact carries information that is often
The way people interact with devices is vital for
implicitly exploited in the exchange of messages.
their success. Looking at HCI it is apparent that
While in a conversation the behavior of
interaction techniques are limited by the
participants as well as what happens in the
technology available. Furthermore the anticipated
surrounding environment supplies valuable
user groups influence the interaction metaphors to
information that is often vital for the
a large extent. Considering the shift from punch
understanding of messages. In many cases the
cards to interactive text terminals and also the
robustness of human-to-human communication is
shift from command line interfaces to graphical
based on the implicitly introduced contextual
user interfaces (GUI) this was observable.
information, such as gestures, body language, and
voice. Another example is redundancy between
Bearing in mind current and upcoming
body language (e.g. nodding) and spoken
technologies, such as increased processing power
languages (e.g. the word ‘yes’). This implicitly
(even on mobile devices), availability of sensors

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introduced knowledge is also used to
rudimentary level, e.g. automatic light control
disambiguate information, e.g. in a discussion
(switches on the light when it is dark and
with a student pointing at a computer the term
someone is walking by) and active badge systems
‘sun’ has a different meaning than the same term
(automatically open a door when someone with
when on the beach together with friends; a more
appropriate permission likes to enter the
in depth discussion is given in [11].
building). In current computer systems we can
observe that agent technology is used to build
2.1
Implicit vs. Explicit Human Computer
systems that have a certain ability to act
Interaction
proactively. These approaches are mainly based
Considering current computer technology
on user profiles and usage information [13]. In
interaction is explicit – the user tells the computer
these cases perception is limited to information
in a certain level of abstraction (e.g. by
gathered in the virtual space.
command-line, direct manipulation using a GUI,
If we look concepts that are needed to facilitate
gesture, or speech input) what she expects the
implicit interaction three basic building blocks
computer to do. This is considered as explicit
can be identified:
interaction.
1. the ability to have perception of the use, the
Definition: Implicit Human Computer Interaction
environment, and the circumstances,
Implicit human computer interaction is an action,
2. mechanisms to understand what the sensors
performed by the user that is not primarily aimed
see, hear and feel, and
to interact with a computerized system but which
such a system understands as input.
3. applications that can make use of this
information.
The action of a user is always performed in a
certain environment. Implicit interaction is based
On a conceptual level (1) and (2) can be
on the assumption that the computer has a certain
described as situational context. And (3) are
understanding of our behavior in the given
applications that are context enabled. In the next
situation. This knowledge is then considered as
section context is discussed in more detail.
an additional input to the computer while doing a
2.2 What is Context
task.
The notion of context is used in many different
A simple example is the garbage bin [14] that
ways. In our work we propose to regard
scans in the bar code of products and reproduces
situational context, such as location, surrounding
the information for a suggested shopping list. The
environment or state of the device, as implicit
action performed by the user (e.g. throw away an
input to the system. We use the term situational
empty can in a bin) is the same as with any other
context to describe implicit interaction fragments.
garbage bin. The recognition of the system (by
This extends the concept of context beyond the
scanning the bar code) and the built-in
informational context into real world
interpretation of the system (all things that go into
environments.
the bin may be on the next shopping list again)
make use of the action performed by the user.
The word Context in general use has a multitude
The user herself does not explicitly interact with
of meanings. Even within the field of computer
the computer, thus the process describes an
science different disciplines, such as artificial
implicit interaction. As we see from the example
intelligence, natural language processing, image
implicit interaction is based on two main
recognition, and more recently mobile computing,
concepts:
have their very own understanding of what
•=
context is. In our work we found that very general
perception
descriptions of context as given by a dictionary
•= interpretation.
and also synonyms found in a thesaurus come

very close to our understanding. To illustrate this
For most applications implicit interaction will be
we like to provide the following definitions:
used additionally to explicit interaction.
Context n 1: discourse that surrounds a
There are other systems implemented that also
language unit and helps to determine its
facilitate the idea of implicit interaction on a
interpretation [syn: linguistic context,

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context of use] 2: the set of facts or
only a few seconds and making a note on a PDA
circumstances that surround a situation or
is often in the range of several seconds up to
event; "the historical context" (Source:
some minutes. Also the fact that the applications
WordNet ® 1.6)
are mainly used while doing something else or to
Context: That which surrounds, and gives
carry out a certain task (like tools in the real
meaning to, something else.
world) calls for a reduction of the explicit human-
(Source: The Free On-line Dictionary of Computing)
machine interaction and creates the need to shift
towards implicit HCI.
Synonyms Context:
Circumstance, situation, phase, position,
Knowledge about the situational context is of
posture, attitude, place, point; terms;
primary interest to the application, because we
regime; footing, standing, status, occasion,
consider that the application will adapt to the
surroundings, environment, location,
context.
dependence. (Source: www.thesaurus.com)
It can be observed that an application (mobile or
To build applications that have knowledge about
stationary alike) is:
their situational context it is important to gain an
(a) running on a specific device (e.g. input
understanding what context is. Current research
system, screen size, network access,
in context-awareness in mobile computing shows
portability, etc.),
a strong focus on location [1], [12]. Location is a
(b) at a certain time (absolute time e.g. 9:34 p.m.,
concept that is well understood. Also the benefit
class of time e.g. in the morning)
of location-awareness is clearly given, at certain
(c) used by one or more users (concurrently or
locations particular services are more important
sequentially),
than others. An architectural approach, based on a
(d) in a certain physical environment (absolute
smart environment is described by Schilit et. al.
location, type of location, conditions such as
[17]. Other scenarios are using RF and GPS to
light, audio, and temperature, infrastructure,
determine the users location, e.g. [4], [15]. But, as
etc.),
pointed out in [20] context is more than location.
(e) social setting (people co-located and social
We use the term context considering mobile
role),
computing in a more general way, as also
(f) to solve a particular task (single task, group
suggested by [2], to describe the environment,
of tasks, or a general goal).
situation, state, surroundings, task, and so on. A
We consider the items (a) to (f) as the basic
wider view of context is also given by [19]. They
building blocks of context. For mobile
suggest to consider the way a device is used
applications especially (d) and (e) are of major
(mobile phone in the users hand, on the table, in
interest. In mobile settings the physical
pocket, etc.) to be treated as context.
environment can change while an application is
executed e.g. making a phone call while walking
2.3 Applications in Context
from the office desk to the car park. The
telephone application is running, while the noise
Analyzing the way people use ultra-mobile
level changes between office and outside.
devices (e.g. personal digital assistants, smart
mobile phones, handheld and wearable
2.4
Identifying Implicit Human Computer
computers) it becomes apparent that the periods
Interaction
of interaction are much shorter than in traditional
To identify applications that can be improved by
mobile settings. Notebooks – considered as
implicit HCI input and output of the application
mobile computers - are mainly used in stationary
and the real world environment in which it is
setting, e.g. one takes a notebook to a meeting
executed have to be analyzed. Then ways to
and takes note and a salesman takes a mobile
capture the situational context must be assessed.
computer to a customer for a presentation. In
Furthermore mechanisms for the interpretation of
general in these scenarios the application is used
the situational context have to be found. Finally
in a stationary setting between several minutes
the reaction of the application has to be defined.
and hours. Whereas considering the usage of
The following questions help to identify these
ultra-mobile devices interaction periods are often
points:
much shorter e.g. looking up an address takes

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•= What happens around an application while
On 3: For each Ci the accuracy Ai and the update
the application is in use? Are there any
rate Ui that are needed to make the measurements
changes at all?
useful are defined. Then a sensing device that
•= Do the surroundings (behavior, environment,
matches these requirements is identified. If the
circumstances) carry any valuable cost for the identified sensing device D is
i
information for the application? Does it
acceptable, then the vector describing the
matter for the application?
condition, the sensing device, the required
•= Are there any means to capture and extract
accuracy and update rate is added to the set D.
the information in a way that is acceptable for
For conditions that cannot be sensed the cost is
the application or device (processing cost,
infinite.
sensor cost, weight, etc.)?
On 4: If any conditions that are feasible to
•= How to understand the information? What
measure exist then for each of these conditions
interpretation and reasoning is possible and
one or more range values that are meaningful
useful. What is an appropriate way for the
(temperature between 15°C and 25°C, location is
application to react?
inside my office, user is moving, etc.) are
identified and for these ranges the reaction of the
Putting all of these together we can set up the
application (switch to notepad, etc.) is defined.
algorithm in figure 1. The algorithm works as
follows:
2.5 Modeling
Implicit
Human Computer
On 1: C is the set of surrounding conditions that
Interaction
carry information that is useful for the
To specify applications that facilitate implicit
application. Each element Ci stands for one
HCI it is inevitable to have a specification
condition, e.g. location, temperature, current user,
language to describe situational context linked to
device orientation, etc. The set is created by
events/change that occur in the application. In our
asking what condition change in the environment.
recent work we found it helpful to use a notation
that is human readable as well as easily to process
On 2: D is initialized – at the beginning no
using a computer. We decided to use a markup
sensing devices are identified.
language that is specified in XML for this
1. create the set C
2. set D = {}
3. for each C ∈ C
i
define Ai. // accuracy
define Ui. // update rate
identify Si // a sensor device
// that is appropriate
if cost(Si, Ai, Ui) is acceptable then
D = D ∪{( Ci, Si, Ai, Ui)}
fi
next
4. if D ≠ {} then
for each vector Di in D


define a set of application reaction Ri = {(Iij, Rij)}
// Iij is input range, application reaction pairs
Iij


// Rij is application reaction
else
// implicit interaction is not used
//(either no condition that are useful or too costly)
Figure 1: Identifying Implicit HCI.

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purpose. Extending the SGML based description
<!ELEMENT context_interaction
model introduced by Brown in [2], [3] we added
(context , action )>
two more concepts - grouping context with
<!ELEMENT context
(group+ )>
matching attributes and trigger attributes to make
<!ELEMENT group
(#PCDATA )>
<!ATTLIST group
match
the description more expressive and suitable for
(one | all | none ) #REQUIRED >
our projects. See figure 2 for the XML data type
<!ELEMENT action
(#PCDATA )>
definition (DTD).
<!ATTLIST action
In the <context> section contextual variables
time
CDATA
’0’
are used to describe the conditions. These
trigger
(enter | leave | in )
variables are made of two parts, the first is used
#REQUIRED >
to specify the context sensing module, in figure 5,
Figure 2: Data Type Definition
the sensor module (sensor_module) and the
palm pilot (pilot) and in the second part the
<context_interaction>
<context>
variables provided by this module.
<group match=’one’>
In the <action> section function calls are used
sensor_module.touch
to specify the action to be carried out in case the
pilot.on
trigger evaluates to true. These calls are also
</group>
hierarchically structured; specifying the device,
<group match=’none’>
sensor_module.alone
the application, and the function to be performed.
pilot.pen_down
Depending on the platform (e.g. context sensing
</group>
module in a microcontroller) we use a different
</context>
implementation language.
<action trigger=’enter’ time=’3’>
pilot.notepad.confidential
If contexts are composed of a number of
</action>
components we found it very helpful to have a
</context_interaction>
mechanism to bundle certain contextual variables
in groups and select a matching semantic for each
Figure 3: Context description
group description. For matching in a group we
provided the following semantics: one (match
In figure 3 an example of a description of a
one or more of the variables in the following
context and an action is shown. The context
group), all (match all variables in the following
description consists of two groups of contextual
group), none (match none of the variables in the
variables. In the first group the match semantics
following group). All groups within the context
is that at least one of the variables must be true, in
description must evaluate to true to cause the
this case either the device is touched or the state
trigger.
of the device is on. In the second group the match
semantics is ‘none’, which means that the
We discriminate three different triggers: ‘enter a
contextual variable
context’, ‘leave a context’, and ‘while in a
alone must not be true and
that the user must not have touched the screen
context’. The ‘enter’ and ‘leave’ triggers take a
with a pen.
time value that specifies the time after1 which the
action is triggered if the context stays stable over
If the context evaluates to true, an action is
this time. For the ‘while in a context’ trigger the
triggered. Here the semantics is that if the context
time indicates the interval in which the trigger is
is entered and is stable for at least three seconds
fired again.
then the action is performed.
The complete description means that if the device
is on or in the users hand and if the user is not

alone and he is not touching the screen with the
1 The parameter indicating the time after that an action is
pen then after three seconds the display should be
performed is often 0 (immediate context action coupling)
hidden by an image as depicted in figure 6 (d) in
or positive. In certain circumstances, when future
the later section.
situations can be predicted (e.g. you drive your car into the
parking, the context walking will appear soon) a negative
value does make sense, too.

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3 Perception
information of this kind is also useful for other
There are several ways to equip devices with
applications, for instance calendars, email
perceptional capabilities. The range of
notification, pagers and mobile phones can make
complexity to consider is very wide, starting from
use of any context that gives an indication of
simple sensors that know the way a device is held
whether or not it is a good time to interrupt a
[18] to complex audio and video analysis. We
user.
identified the following four basic approaches:
The specific contexts that we chose for our study
•= device-databases (e.g. calendars, todo-
are based on aural information: user speaking,
lists, address books, profile, etc.)
others speaking, noisy, and quiet. And based on
•=
movement of the user: walking, running,
input to the application running (notepad
stationary. Movement context was included as it
- taking notes, calendar - looking up a
gives an indication as to whether a user can be
date, etc.)
interrupted visually.
•= active environments (active badges [10],
For recognition of aural and movement contexts,
IR-networks, cameras, audio, etc.)
we integrated two microphones and an
•= sensing context using sensors (TEA [5],
accelerometer in our design. One of the
[21], Sensor Badges [1], GPS, cameras,
microphones is placed near the user’s throat, the
audio [16], etc.)
other pointing away from the user. With this
The perceptual capabilities can be located in the
configuration the distinction of speaker and
device itself, in the environment or in another
environment is feasible with minimal processing
device that shares the context over a network (e.g.
cost. The acceleration sensor is used to
body area network).
discriminate whether a user is standing still,
In the remainder of this section we concentrate on
walking or running.
sensor based perception, also knowing that in
The sensor placement considerations led us to
most scenarios a combination of all four cases is
build the context-awareness component into a tie
the way of choice. First we introduce two sensor
– it may be considered to build them into other
devices developed in our group and then provide
accessories worn in similar ways (e.g. jewelry,
some information on other sensor based devices
neckerchief, or necklace). We also liked that a tie
that supply contextual information.
stresses the component’s design as accessory
rather than as stand-alone device, see figure 4.
3.1 Context Awareness Component
The hardware of our context-awareness
In this part a wearable context-awareness
component is build around a TINY-Tiger
component that integrates low-cost sensors is
microcontroller, which offers four analog inputs
described. Simple methods are used to derive
context information from sensor data. The
derived context is application-independent and
can be exploited by other wearable or personal
technologies in a body network, for instance
wearable computers, mobile phones, digital
cameras, and personal digital assistants.
Here we chose to address a number of contexts
that relate to how interruptible the user is. These
contexts describe only a certain aspect of real
world situations but they are general in the sense
that they can be exploited by a range of
applications. Such context is for instance
implemented and used in the audio wearable
described in [16], mimicking the human ability to
recognize situations in which it is rude to
interrupt, for instance when a person is engaged
in a conversation or giving a talk. Context
Figure 4: Context-Awareness Tie.

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and two serial lines. The two signals from the
3.2 Sensor Board
microphones are amplified and connected to the
Using this Board we collect data on the
analog inputs. To measure the motion we used a
situational context by using a combination of low
two-axis accelerometer (Analog Devices
level sensors. In this project we built a context
ADXL202). A more detailed description has been
recognition device equipped with a light sensor,
published in [22].
acceleration sensor, a passive infrared sensor, a
The software is realized in Tiger-BASIC, a
touch sensor, and a temperature sensor. All
multitasking basic dialect for the TINY-Tiger. It
sensors, but the touch sensor are standard sensors
reads and analyzes sensor data in a time window
and produce analog voltage level. The touch
of about four seconds. The methods to analyze
sensor recognizes the human body as a capacitor
the signals are deliberately simple; they work
and supplies a digital value. The heart of the
within the time domain and are based on basic
device is a BASICTiger microcontroller that reads
statistical measurements. Based on the features
from all the physical input channels (it offers four
calculated from sensor data the contexts are
analog digital converters and a number of digital
detected.
IOs) and statistical methods are applied to
The communication is based on a serial line
recognize contexts. The board is depicted in
connection using 9600 bit/s, in a simple request-
figure 5. The PDA requests contextual variable
reply manner. The client requests the contextual
while the application is idle, e.g. catching the
variables from the context-awareness component
NullEvent on the PalmPilot.
that sends back the variables together with the
values.
3.3 Related Work on Context Sensing
Experimentation with the context-aware tie
In robotics this way of perception is widely used
showed that contexts were recognized in a very
but with a different objective – giving machines
reliable way. Both ‘user speaking’ vs. ‘others
the ability to operate autonomously.
speaking’ and ‘stationary’ vs. ‘walking’ vs.
For the use with handheld devices the project
‘running’ were discriminated correctly. A key
TEA [5] developed a sensor board (equipped with
finding is that sensor placement can be used
8 sensors, light, acceleration, pressure,
effectively to increase reliability and to reduce
temperature, etc.) that supplies contextual
required processing.
information; communication is done via serial
The device can provide information on the
line. The application described is a mobile phone
situational context of the user for other personal
that recognizes its context (in users hand, on the
technologies in a body area network. Using this
table, in suitcase, outdoors) and it adapts ringing
device the implicit HCI can be facilitated.
modes according to users preferences in that
situation [19].
Using a similar approach a system to facilitate
indoor location awareness based on low level
sensors is described in [8]. The system reads data
from different sensors (acceleration, light,
magnetic field, etc.) and provides location
information.
In [7] a cup is described that has an acceleration
and temperature sensor build in together with a
microcontoller and infrared communication. The
cup is aware of its state (warm, cold, on a table,
drinking, moved). The information from a
number of cups communicated to a server is then

used to supply information about the group of
users. All these projects focus on a completely
Figure 5: Context Sensing Device and
sensor based approach to context awareness.
PalmPilot
A jacket that knows if it is on the hanger or with
the user is presented in [6]. The sensor jacket has

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woven in sensors that give information if the user
concern. Implicit HCI does not solve these
is wearing the jacket, what movements the user is
problems in general but can help to:
making, etc. As one application correcting
•= adapt the input system to the current situation
movements in sports (automated tennis coach) is
(e.g. audio filter, recognition algorithms, etc)
suggested in the paper. In this project the
•= limit need for input (e.g. information is
development of robust sensing technology is very
already provided by the context and can be
central.
captured)
•
4
How Can HCI benefit from
= reduce selection space (e.g. only offer
Context?
appropriate options in current context)
HCI for mobile devices is concerned with the
4.3 ContextNotePad on a PalmPilot
general trade-off between devices qualities (e.g.
To explore ways of implicit communication
small size, light-weight, little energy
between users and their environment with mobile
consumption, etc.) and the demand for optimal
devices we built a context aware NotePad
input-output capabilities. Here implicit HCI can
application. The system uses the perceptional
offer interesting alternatives.
capabilities of the sensor board, described in the
previous section and provides an application that
4.1 Output in Context
is very similar in functionality as the built-in
Over recent years the output systems for mobile
notepad application on the PalmPilot.
devices became much better; features such as
Additionally the application can adapt to the
stereo audio output, high-resolution color screens
current situational context and can also react in
for PDAs and even on mobile phones as well as
this way to the implicit interaction. The
display systems for wearable computers are
application changes its behavior according to the
commercially available. Also unobtrusive
situation. The following context adaptations have
notification mechanisms (e.g. vibration) have
been implemented.
become widely used in phones and PDAs. Still on
•= On/Off. The user has the device in her hand.
the lower end devices with very poor display
In this case the application is switched on, if
quality enter the marked. Situational context can
the user is putting the device out of her hand
help to:
it is switched off after a certain time. It
•= adapt the output to the current situation
assumes that if the user takes the device in
(fontsize, volume, brightness, privacy
her hand she wants to work with the device.
settings, etc) [19].
•= Fontsize. If the device is moved (e.g. while
•= find the most suitable time interruption [16],
walking or on a bumpy road) the font size is
[22].
increased to ease reading. Whereas while
•= reduce the need for interruptions (e.g. you
having the device in a stable position (e.g.
don’t need to remind someone to go to a
device stationary in your hand or on the table)
meeting if he is already there.)
the font is made smaller to display more text
at the same screen, see figure 6(a) and(b).
4.2 Input in Context
•= Backlight. This adaptation is straightforward
Considering very small appliances the space for a
but still not build in in current PDAs. By
keyboard is very limited what results in bad
monitoring the light condition the application
usability. Other input systems, such as graffiti and
switches on the backlight if the brightness
handwriting recognition have been developed
level in the environment is below a certain
further but still lack in speed and accuracy [9].
threshold. Accordingly if it becomes brighter
Advances in voice recognition have been made in
the light is switched off again, see figure 6(c).
recent years, but for non office settings (e.g. in a
•=
car, in a crowded place, sharing rooms with
Privacy settings. If you are not alone and
others, and in industry workplaces), the
you are not writing (or touching the screen)
recognition performance is still poor. Also
the content on the display is hidden by an
privacy and acceptance issues are a major
image, see figure 6(d). To sense if someone is

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Figure 6: Adaptation to Context a) small font, b) large font, c) backlight, d) privacy
walking the passive infrared sensor is
From current projects we learned that there is a
deployed.
need for a simple specification language for
Currently we decrease the size of the context-
implicit HCI, based on situational context. We
awareness device to make it feasible to plug it
propose an XML-based markup language that
into the pilot to allow proper user studies.
supports three different trigger semantics. The
language is easily human readable and also easy
to process.
5 Conclusion and Further Work
Basic mechanisms of perception to acquire
Based on observations of new sensing
situational context are discussed. In the first
technology, available sensors and anticipated
example a wearable context awareness
users a new interaction metaphor is proposed.
component build into a tie is described. Also a
Implicit HCI is defined as an action, performed
sensor-based context-awareness device is
by the user that is not primarily aimed to interact
introduced. Both devices supply context to other
with a computerized system but which such a
devices over a simple request reply protocol over
system understands as input. It is further
the serial line.
identified that perception and interpretation of the
user, the environment, and the circumstances are
In a further section benefits of implicit interaction
key concepts for implicit HCI. Furthermore
trough situational context to HCI are discussed.
applications that exploit this information are
In an example implementation the feasibility of
required.
the concepts introduced earlier is demonstrated.
Perception and interpretation are considered as
situational context. Therefore we motivate a
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