The document describes a methodology for parameterizing cognitive user models within the VERITAS project. It involves identifying cognitive parameters from literature and relating them to ACT-R parameters and tasks. An analysis of ACT-R identified it as a suitable cognitive architecture for modeling users with disabilities. The methodology defines cognitive profiles for elderly users and those with Alzheimer's or Parkinson's. Overlays are used to modify ACT-R parameters to represent cognitive impairments. Abstract cognitive models are created and related to ACT-R parameters and tasks. This will allow generating virtual user models representing individuals with specific disabilities.

1. A New Approach Parameterization of Cognitive
Disabilities
Ivo Ramos Maia Martins*1, María Fernanda Cabrera-Umpiérrez*2, Maria Teresa Arredondo*3, Ana María Navarro
Cerdá2
*
Life Supporting Technologies, ETSIT- UPM
Avda. Complutense 30, Madrid, Spain
1
iramos@lst.tfo.upm.es
2
chiqui@lst.tfo.upm.es
3
mta@lst.tfo.upm.es
#
Asociación ITACA
Instituto ITACA, Universidad Politécnica de Valencia. Camino de Vera s/n. 46022. Valencia (Spain)
2
annacer@itaca.upv.es
Abstract— This paper focuses on the description of the approach validated within VERITAS, focusing on those models that can
used to parameterize the cognitive user models developed under represent the different cognitive, psychological and perception
the FP7 EU Founded project VERITAS: Virtual and Augmented processes of elderly, cognitive impaired and physical impaired
Environments and Realistic User Interactions To achieve people.
Embedded Accessibility DesignS. The methodology defined
consists on the identification of standards, rules and guidelines
In order to create cognitive models of the target users that
found on the literature to categorize the cognitive attributes. To can be used within VERITAS accessibility tools, it is
complete the parameterized cognitive user model it was created a necessary to identify which are the cognitive and
relationship between ACT-R parameters, the affected tasks and psychological functions and corresponding parameters (e.g.
the cognitive parameters. A research on existing ACT-R models reaction time, perception, attention, working memory, etc.)
is still being carried out in order to obtain functions and values that are related with the defined VERITAS cognitive
that can be suitable for the VERITAS parameterized cognitive impairments and to define recommendations, guidelines and
user models table. The development of the previous method will values that will support the designers and developers’
provide useful information to complete this parameterization. decisions at the moment of creation of new products and
Futures steps will consist on the integration of the parameterized
cognitive user models into the virtual user models.
services.
Our paper will focus on the methodology used to define the
I. INTRODUCTION relevant cognitive parameters within the context of VERITAS.
The use of existing models of the cognitive architecture
Nowadays there is a continuous ageing of the European
Adaptive Control of Thought-Rational (ACT-R) and the
population. It is very important to provide the maximum of
relationship with existing medical studies are the main focus
independence to elderly people and people with cognitive
of our study.
impairments such as cognitive ageing, Alzheimer and
Parkinson Disease. The development of products and services II. STUDY DESCRIPTION & METHODOLOGY
accessible to everyone is the correct way to achieve the
population requirements in the future. The study description will help to understand the context of
With this objective, VERITAS project is aiming to this study within VERITAS project as well as the used
operationalize and revolutionize the accessibility testing at all methodology for modeling VERITAS users.
stages of creation of new products in the considered five A. VERITAS User Modelling Methodology
industrial domains (Automotive, Smart Living Spaces,
Virtual user modelling is considered as the core research
Workplaces, Infotainment and Healthcare) ¡Error! No se
issue in VERITAS. The virtual user models will be generated
encuentra el origen de la referencia..
based on existing standards and guidelines but also based on a
The goal is to introduce simulation-based and virtual reality
multisensorial platform designed and implemented within
testing at all stages of the design process in order to ensure
VERITAS that will “sense” the needs of real users with
that future products and services can be “universally” used,
disability by measuring their behaviour in simulated
including people with disabilities and elders. For creating VR
environments [1].
tools with high acceptability amongst users, not only physical,
Since, virtual user modelling with disabilities is considered
but also cognitive and psychological models that represent the
a very challenging task which is not yet fully developed, not
cognitive capabilities should be integrated in the design
even at research level, VERITAS will follow an innovative
process.
approach of generating virtual user models based on
Different theories of human cognitive & psychological
combining the results of three different but complementary (in
modelling and interaction should be therefore integrated and
most of the cases) approaches. Thus the Virtual user

2. modelling process of VERITAS consists of the following generate, including relevant parameters, measurements and
steps: metrics found in literature and computational modelling
- Abstract User Models (AUM) creation that can be approaches.
implemented within VERITAS based on Analysis of These models will be - in a second step - refined with the
existing models, medical studies, guidelines, Multisensorial platform.
methodologies and existing practices, User needs and The Multisensorial platform is used to fine tune the virtual
well known accessibility guidelines and standards. models with the result of the interaction of real users and the
An AUM represents the different facets of a virtual environments and to provide feedback for quantitative
disability. evaluation and verification of the user models [1].
- Appropriate Task models implementation, based on On one hand, an initial research was made in order to
UIML/USIXML language, when users performing determine the most relevant cognitive processes in the context
specific tasks and interactions of the cognitive disabilities to be used for representation of the
- Iterative update and verification of the models using abstract cognitive user models. These processes were divided
the implemented VERITAS multisensorial platform. in two major groups: basic and higher-level processes.
- Generation of Generic Virtual User Models (GVUM), The basic cognitive processes are composed by reaction
by merging the Abstract User Model with the time, attention (which is subdivided in selective, divided and
affected tasks per disability. sustained), memory (subdivided in semantic, episodic,
- Creation of the Virtual User Models, by instantiating procedural and working) and perception (subdivided in visual,
the GVUM, which represents a specific user with a auditory and haptic).The higher-level group is composed by
disability/s. decision making, orientation, and speech and language [2].
Once the relevant cognitive processes were selected, the
In the following scheme, the steps followed in VERITAS following step was to determine how the different cognitive
for creating a model can be seen: disabilities - Alzheimer, Parkinson and cognitive ageing -
affects on the cognitive processes. With this aim, a deep
research in medical literature was performed. Table 1
represents the change or affect of the cognitive processes in
the normal elderly, early DAT, and early PD. The losses are
qualitatively indicated by the + sign. A greater number of
crosses indicate a more pronounced degree of severity [2].
TABLE I
COGNITIVE PROFILES OF THE ELDERLY AND PATIENTS WITH DEMENTIA OF
ALZHEIMER’S TYPE (DAT) AND PARKINSON’S DISEASE (PD)
Figure 1 - Representation of the architecture of the VERITAS SP1,
methodology to create the virtual user models
Ontologies will be used to provide a powerful and growing
specification of the abstract user models. An abstract user
model stored in the ontology will include the type of user
disability, user capabilities, user needs, characteristics from
cognitive user models, physical user models, behavioural &
psycholological user models, guidelines and standards.
In the following sections, each element of this schema will
be further detailed under the cognitive perspective.
B. Abstract Cognitive User Models
An Abstract User Model (AUM) is a descriptive
representation of the different dimensions of a human being.
In Veritas, a cognitive abstract user model of each cognitive
disability categorizes the representative features of the
cognitive and psychological facets of an individual:
definitions, types, cognitive functional limitations that may

3. On the other hand, under the perspective of VERITAS measured by comparing the results of the model with the
domains (Automotive, Smart Living Spaces, Workplaces, results of people doing the same task [2].
Infotainment and Healthcare), existing approaches (mainly ACT-R is a hybrid cognitive architecture: its symbolic
computational and cognitive architecture models such as structure is a production system, whereas the subsymbolic
ACT-R, GOMS, GOMS-Simple, ACT-Simple, EPIC, SOAR, structure is represented by a set of massively parallel
PUM, ANNs, Fuzzy Logic and Markov) that address and/or processes that can be summarized by a number of
model aspects of the cognitive processes were analyzed [2]. mathematical equations, with parameters. The subsymbolic
A state of art with the strengths and weaknesses of these equations control many of the symbolic processes. For
modeling approaches was performed. This analysis pointed instance, whether (or how fast) a fact can be retrieved from
out ACT-R as the most promising and extended modelling declarative memory depends on subsymbolic retrieval
approach, that is consistent with the Abstract User Model equations, which take into account the context and the history
intended in VERITAS: an explicit descriptive model of human of usage of that fact.1
cognition and behaviour that can be afterwards parameterized. ACT-R architecture allows, through the subsymbolic
In the following section a complete analysis of ACT-R as structure with parameters, and the symbolic structure (task
reference cognitive architecture will be shown. models) the generalization of new situations, users and
domains, which means that allows a wide variation among
C. The ACT-R research approach models.
The cognitive architectures are theories to simulate and
understand how the human mind works. They are based on D. Cognitive moderators in ACT-R: Disabilities as overlays
cognitive psychology theories and assumptions and are An overlay is a technique for including a theory of how a
implemented in a computer program that uses knowledge moderator (ie: aging) influences cognition across all models
representations to reproduce the human thinking [3] . within a cognitive architecture [4]. An overlay is an
The Adaptive Control of Thought-Rational (ACT-R) was adjustment or set of adjustments to the parameters or
the selected cognitive architecture to obtain the missing values mechanisms that influence all models implemented in the
and parameters for the different disabilities. It provides a architecture to reflect changes due to an altered mental state or
conceptual framework for the creation of the models of how due to long term changes such as development [5]. The main
people will perform the tasks. It reproduces assumptions about idea of an overlay is to change the architecture in such a
the human cognition based on facts resultant from psychology manner that the behavior of all models developed under that
experiments. ACT-R uses a modular organization, which architecture will be affected.
means that the cognition emerges from the interaction of In many architectures, such as the one described here,
independent modules, each of them is related with a function ACT-R, there are a set of mechanisms and a number of
and specific regions of the brain (Figure 2)[2]. parameters that play a role in the model’s functioning; an
overlay will modify a combination of parameters and
mechanisms to represent situation specific but relatively long
acting changes to information processing. For example, an
eyeglasses overlay would allow more inputs to be passed to
the vision processor; a caffeine overlay could increase
processing speed by 3% and improve vigilance by 30% [4].
Overlays are based on popular theories and studies about
cognitive and behavioural moderators that can be applied to
cognitive architectures. The goal is to specify mechanisms
that can be implemented within the architecture or changes to
current mechanisms to simulate the effect of the cognitive
impairments on embodied cognition.
These theories are typically not cast as additions to the
knowledge necessary to perform a task (it would mean
creating a cognitive model), but are described as changes
to how people process information under a psychological
state. Thus, they make suggestions about process, about how
the mechanisms of embodied cognition change across all tasks
under this facet.
In the case of VERITAS, an analysis was performed in
Figure 2 - ACT-R 6.0. Each ACT-R module is associated with a function order to determine these overlays: the values of the parameters
(from the subsymbolic structure) per cognitive disability that
Different models written in ACT-R are created per each
task. Beside the incorporation of the ACT-R’s view of
cognition it is necessary to incorporate assumptions about the
particular task. The veracity of these assumptions can be 1
http://act-r.psy.cmu.edu/about/

4. were related with the cognitive processes (high level and low- TABLE II
RELATION BETWEEN ACT-R (SGP) PARAMETERS AND VERITAS COGNITIVE
level) detected in the AUM. PARAMETERS
After that, a wide literature research has been conducted in
order to extract the values of these parameters for the different
VERITAS end-users: elderly and cognitive impaired in
different domains.
For example, the ACT-R parameter activation spread (:ga)
of the goal module is related with the VERITAS basic
cognitive process memory. According with the research made
so far it is possible to say that the value of the activation
spread parameter (:ga) for moderate Alzheimer is 0,68.
Currently, an ongoing research is focusing on extracting
production task models that correspond to the primitive
cognitive task models defined in VERITAS,
The final development of the ongoing research will provide
useful information to complete the parameterized cognitive
user models. One of the major difficulties is the large
unpredictability and variability that different persons with the
same cognitive problem can have while performing the same
task. To improve the obtained results, would be necessary a
large research in collaboration with psychologists and users in
order to develop ACT-R models per each task.
E. Virtual User Models
The creation of Virtual User Models is considered as the
core research issue in VERITAS. They will be generated from
an instantiation of the Generic Virtual User Models [6].
Their creation is based on the result of the unification of the The ACT-R parameters listed in the table II, intrinsically
Abstract User Models, the collection of parameters, the ACT- (meaning at a subsymbolic level) correspond to a specific
R productions that are related with the primitive tasks, the ACT-R module (Figure 2), which, at the same time, are
result of the measurements and the feedback of real users related with the different cognitive processes relevant for
obtained with the Multisensorial Platform. VERITAS previously described.
Literature has shown that two disabilities may share the
same parameters and value – for instance, medical literature
shows that Parkinson and Alzheimer at level 1 have the same
CRD value –. In those cases, we can use analogy to transfer
the value of the corresponding ACT-R parameter of a specific
disability (Alzheimer) to the same parameter of the other
disability (Parkinson).
The use of results from medical studies is then a useful way
Figure 3 - Process of creation of the Virtual User Model to obtain values for overlaying the equations that represents
the cognitive processes.
The Generic Virtual User Models will be used by the user So far we have 5 ACT-R (sgp) parameters related with
model generator to create instances of the Virtual User cognitive ageing, 12 related with Alzheimer’s disease and 5
Models per each application scenario (Figure 3) [6]. related with Parkinson’s disease. All these values are related
The Virtual User Models will be described with the use of as well with the VERITAS cognitive processes and primitive
ontologies for the representation of the Abstract User Models tasks.
and UIML/USIXML files for the association of the virtual
users with tasks. The final step is their inclusion on the IV. CONCLUSIONS AND NEXT STEPS
simulation platform in SP2 (Innovative VR models, tools and Though the study is not yet finalized, so far we are able to
simulation environments) [7]. conclude that it is possible to find ACT-R studies related with
the VERITAS cognitive parameters which will be relevant to
III. RESULTS
model VERITAS end-users with cognitive impairments.
Table II shows the list of the ACT-R (sgp) parameters Mostly, the parameters are values and ranges.
found so far in literature and medical studies that are It is also important to refer that with the research in medical
connected with VERITAS primitive tasks and cognitive studies related with the disabilities previously referred, we
processes. were able to find values (i.e. CDR of Alzheimer studies with

5. the Parkinson’s disease) that were useful to use as well in the
ACT-R modelling process.
Finally, it has to be mentioned that to improve the obtained
results and to extract missing values, a large research in
collaboration with psychologists and users would be necessary
in order to develop ACT-R models per each task.
ACKNOWLEDGMENT
Authors thank the VERITAS consortium for their
contribution to this work.
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