A Syndetic Approach to Human Computer Interfaces
by Giorgio Faconti and Mieke Massink
With the advent of new multimedia interaction technologies, the challenge
is to demonstrate their usability. The role of human cognitive abilities
is becoming increasingly important. It must be possible to reason about
usability long before a system is built or even designed. In the early
stages, the most important issues are requirement capturing and the development
of an abstract design specification. As no prototypes of the human computer
interface are available at that point, no experimental information can
be obtained about its usability. A theoretical model of the cognitive aspects
of human information processing can help to reason about the requirements
for the interface. Unfortunately, traditional software engineering and
system design methods do not offer the necessary support for this reasoning.
Our research attempts to fill this gap by expressing user and system
representations in a common framework. The aim is to develop a theoretical
background of cognition that provides a basis for arguing whether an interface
is successful, discovering potential problems and suggesting solutions.
Our approach does not aim at substituting existing methods of interface
design but at achieving a qualitatively better initial design from which
to begin an iterative design process.
In previous approaches, theoretical psychologically-based models have
been used indirectly. We now directly adopt cognitive models within the
specification process, as factors that affect usability depend on psychological
and social properties of cognition and work, rather than on abstract mathematical
models of programming semantics. Claims made through formal methods about
a system's usability must, therefore, be grounded in some psychological
or social theory.
Although in principle any cognitive theory could be adopted, we address
Phil Barnard's Interacting Cognitive Subsystems (ICS), shown in the figure,
in which a gesturing configuration is deployed. We formally model aspects
of this theory so that it can be combined with a system specification following
the syndetic modelling approach developed within the ESPRIT BRA AMODEUS
project.
The 'Interacting Cognitive Subsystem' model with the gesturing configuration.
The word syndesis comes from the ancient Greek meaning to bring together.
It conveys the idea of being able to reason about complex systems as a
whole while keeping the capability of isolating and reasoning about their
basic components. In our case, the syndetic model of an interactive system
extends the formal model of its interface with the model of the cognitive
resources needed to interact with the devices. The formal model of the
system on its own provides few insights into the usability of its interface,
while the formal model of ICS supports general claims about the user's
cognitive processes but not about the effective use of cognitive resources
in a given context. However, combining them in a syndetic model, we can
reason about how cognitive resources are mapped onto the functionality
of the system.
Currently, two different modelling approaches have been investigated:
the first is based on the Modal Action Logic (MAL), the other on a functional
data flow approach. In the first approach, the various components, such
as interaction devices, system and user, are modelled as interactors
object-like entities with an internal state, a presentation and actions
that bring about changes to the state. The behaviour of each interactor
can be formulated as an axiomatic model. In this way, both the user's cognitive
resources and the behaviour of the interface can be described in the same
framework, allowing for an integration of different models at a relatively
high level of abstraction.
In the second approach, it is recognised that the structure of the cognitive
ICS theory closely resembles a data flow oriented approach. The formal
model and the more informal psychological model remain similar which is
an advantage in multi-disciplinary discussions. The ICS concepts we address
are the formal modelling of the continuous flow of information between
subsystems and the transformation of these flows. Since the information
flow is not always linear from the sensory subsystems to the effector subsystems,
interesting problems concern the delay and synchronisation of information.
The speed of information processing depends on the particular cognitive
configuration, and the ability of the processes to operate on the available
information. The delay observed between a stimulus and a response depends
on whether a particular reaction has been proceduralised by the processes
involved, or whether a level of reciprocal interchange of information or
buffered processing of information is needed to interpret the available
information. These differences are well-illustrated by the data flow approach
and within this formalism we can formulate solutions for delay-related
synchronisation problems. These solutions can be matched with results obtained
from psychological experiments on human information handling.
The ICS model has been applied to the evaluation of gesture-based Human
Computer Interfaces and of a more complex case of deitic reference employing
gesture and speech. This work has shown that a formalisation of certain
aspects of human behaviour is valuable in evaluating usability aspects
based on initial formal designs of interfaces. Moreover, a more precise
mathematical model of cognitive aspects can help to improve cognitive theory
by raising new questions about its contents and application. These in turn
can shed new insights into design issues for interactive systems. The formulation
of the cognitive theory in a formal framework has the advantage that it
can be easily introduced and explained to the computer science community.
Please contact:
Giorgio Faconti or Mieke Massink - CNR-CNUCE
Tel: +39 50 593 241
E-mail: G.Faconti@cnuce.cnr.it
and M.Massink@guest.cnuce.cnr.it
