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models have been developed. An interesting overview can be found in Ortony (1997). Among
the models cited in Ortony (1997), the model by Ekman have been chosen as basis for our
work. According to Ekman's model, there are six primary emotions: anger, disgust, fear, joy,
sadness, surprise. We have developed a reduced version of this model, including only three
of the listed basic emotions: anger, joy, sadness. We selected them as basis to express humor.
At this moment our agent is able to express one of these three emotions at a time, with a
variable intensity level. The emotional state of the agent is represented by a couple of values:
the felt emotion, and its corresponding intensity. The state is established on the basis of the
humor level detected in the conversation. As just said, there are only three possible values
for the humor level. These levels have to correspond to a specific emotion in the chatbot,
with an intensity level. The correspondence should to be defined according to a collection
of psychological criteria. At this moment, the talking head has a predefined behavior for its
humorist attitude useful to express these humor levels. Each level is expressed with a specific
emotion at a certain intensity level. This emotional patterns represent a default behavior for
the agent. The programmer can create a personal version of emotional behavior defining
different correspondences between humor levels and emotional intensities. Moreover, he can
also program specialized behaviors for single steps of the conversation or single witticisms,
as exceptions to the default one.
The established emotional state has to be expressed by prosody and facial expressions. Both
of them are generated by the EMOTIONAL AREA . This task is launched by AD HOC AIML tags.
4. EHeBby talking head
Our talking head is conceived to be a multi-platform system that is able to speak several
languages, so that various implementations have been realized. In what follows the
different components of our model are presented: model generation, animation technique,
coarticulation, and emotion management.
4.1 Face model generation
The FaceGen Modeler FaceGen (2010) has been used to generate graphic models of the 3D
head. FaceGen is a special tool for the creation of 3D human heads and characters as polygon
meshes. The facial expressions are controlled by means of numerical parameters. Once
the head is created, it can be exported as a Wavefront Technologies .obj file containing the
information about vertexes, normals and textures of the facial mesh. The .obj is compliant
with the most popular high level graphics libraries such as Java3D and OpenGL. A set of
faces with different poses is generated to represent a “viseme”, which is related to a phoneme
or a groups of phonemes. A phoneme is the elementary speech sound, that is the smallest
phonetic unit in a language. Indeed, the spoken language can be thought as a sequence of
phonemes. The term “viseme” appeared in literature for the first time in Fischer (1968) and
it is equivalent to the phoneme for the face gesture. The viseme is the facial pose obtained
by articulatory movements during the phoneme emission. Emotional expressions can be
generated by FaceGen also. In our work we have implemented just 4 out of the Ekman basic
emotions Ekman & Friesen (1969): joy, surprise, anger, sadness. The intensity of each emotion
can be controlled by a parameter or mixed to each other, so that a variety of facial expressions
can be obtained. Such “emotional visemes” will be used during the animation task. Some
optimizations can be performed to decrease amount of memory necessary to store such a set
of visemes. Just the head geometry can be loaded from the .obj file. Lights and virtual camera
parameters are set within the programming code. A part of the head mesh can be loaded as
a background mesh and after the 3 sub-meshes referred to face, tongue and teeth are loaded.
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