2 MATHEMATICAL
REPRESENTATION AND
STRUCTURE OF FUZZY
COGNITIVE MAPS
Methodological background of proposed approach is
based on a fuzzy cognitive maps as an extension of
knowledge maps first proposed by Robert Axelrod, a
political scientist, in 1976 (Axelrod, 1976). They
were used to present social scientific knowledge. A
fuzzy cognitive map is presented in the form of a
directed graph which can be represented in the
following manner (Froelich and Juszczuk, 2009):
<N,w>
(1)
where:
N = [N
1
,…N
n
]
T
- map factor values related to each
other by means of dependencies,
w = {w
ij
}- connection weights assigned to the edges
between nodes x expressed in the form of relation
matrices, where are w
ij
are numbers from the
interval [-1,1]; i,j = 1,….n, n- a number of factors.
Every edge w
ij
is related to a given node N
n
and
has an attributed value. The value demonstrates a
kind of relations between factors. If an edge of a
node N
1
to a node N
2
has a value of > 0, it means a
positive influence of a factor A on a factor B. If an
edge coming from the factor B in the direction of A
has a negative value, it means that the factor B has a
negative influence on the factor A. When a value of
the edge equals 0, there is no mutual factor
influence. One needs to point out that the weight of
the edge w
ij
≠ w
ji
. A disadvantage of cognitive maps
was a presentation of relations between factors. The
presentation showed only a kind of connection.
Kosko suggested a change of a method for
determining node connection force (Kosko, 1986)
(Kosko and Postma, 1988). Instead of using marks
only, each edge had an assigned number which
determined the level of connection between
examined factors. Presented values were in the range
of [-1,1]. Consequently, the relations between
the factors could be described by means of fuzzy
terms, such as weak, medium or strong
(Kosko, 1986). The factor value depends
on determining map dynamics with a formula:
1
x
t
∗w
(2)
where: i,j - factor numbers (i,j = 1, …n); n-
the number of factors; f - threshold number; t -
discreet time, x
i
- a value of i-th factor ; w
ij
– a value
of edges between a factor x
i
and a factor x
j
(Froelich
and Juszczuk, 2009). The construction of a fuzzy
cognitive map is based, to a large extent, on input
date. This methodology uses the knowledge
of indicated subjects to represent their experiences
and behaviour by means of a map. The indicated
way of gathering information is subjective,
therefore, it is necessary to collect possibly
the largest group of experts or to rely on research
which included a broad sample (Sobczak, 2007).
Therefore, in the first stage one needs to gather main
factors which have the most vital influence
on a analysed phenomenon. The factors are chosen
on the basis of the number occurrences. If a factor,
among many independent experts’ opinions, occurs
many times, it ought to be included in the model
(Sobczak, 2007). The next step is to indicate
connections between the selected factors.
The connections need to be indicated on the basis
of real mutual factor interaction. Determining edges
and their direction allows defining interaction force
between them and it is determined on the basis
of experts’ knowledge. Interaction force of a relation
C
i
with regard to C
j
can be described by means of
linguistic variables (Papageorgiou and Kontogianni,
2011). Having assigned linguistic values from a set
T to the edges of the map one can determine
a numerical value to every edge. The fuzzification
of the obtained dependences between the nodes
of the map improves mapping of real relations
between the elements of the researched environment.
3 MODEL ASSUMPTIONS AND
THE EYE TRACKING
EXPERIMENT
The universality of FCM is expressed in its wide
application in various areas. In the literature one can
find examples of its application in solving
engineering (Mohr, 1997), industrial (Stylios
and Groumpos, 2004), military (Kosko, 1988)
or economic problems (Tsadiras and Margaritis,
1999). Cognitive maps can also be adapted to solve
problems related with the optimization of an online
advertising message. The issue of optimization
is concerned with dynamic changes of content
of an advertising message and its multitude.
By applying FCM one can quickly define
the effectiveness of a given combination and choose
the most favourable one. Such an approach
minimizes the time spent on keeping online low-
efficiency advertisements. Furthermore, in order
to minimize human contribution like in surveys