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6.4. Eye-tracking for Interaction
6.4 Eye-tracking for Interaction
In this experiment, our aim was to evaluate and validate our application allowing interaction
between a user and a virtual character using gaze. As in the previous experiments, we used
the combination of eye- and head-tracking described at the beginning of this chapter. The
subjects participating in the experiment were seated in front of our back-projection screen
on which we projected the bar environment depicted on the middle left of Figure 3.1. As
explained in Chapter 3.3, our application then receives the eye-tracking and the head-tracking
data and determines whether the user is looking at the virtual character or not. When the user
is looking at the character, hence, when the tracking coordinates are within the bounds of the
virtual character projected on screen, this character demonstrates positive attitudes, shows
interest in what the user is saying and looks back at him/her. On the other hand, when the
user is not looking at the character, hence, when the tracking coordinates are outside the
virtual human bounds, this character’s attitude changes and becomes bored and distracted.
The character looks away, at the ceiling or in other directions, sighs, or looks at his/her
fingernails or watch.
6.4.1 Experimental Protocol - Healthy Subjects
Our hypotheses before conducting this experiment were the following: first, we believed that
the subjects would evaluate a character changing behavior as more realistic than a character
being always attentive or always distracted. Secondly, we believed that the subjects would
consider a character changing attitude with respect to the user’s eye contact behavior as
more realistic than a character that randomly changes behavior. In order to evaluate our
application, we have conducted an experiment in which 12 healthy people were asked to
talk to a virtual character in a bar environment for a couple of minutes. These subjects
were not from any specific socio-economical background. However, they were all aged
25 − 35. The exposure was four-fold; each of the subjects was exposed during 2 to 3 minutes
to four different characters, depicted in Figure 6.11: one which was always attentive and
demonstrated a positive attitude, one which always looked away from the user and seemed
bored and distracted, one which randomly changed attitude between attentive and distracted
throughout the session, and one that changed attitude depending on the subject’s eye-contact
behavior. More specifically, in this last case, the virtual character looked at the user and
seemed attentive and interested when it was being looked at. On the other hand, it lost
interest and even seemed bored when it was avoided by eye contact. The four versions of
this same scene were set in front of each of the 12 subjects in pseudo-random order. However,
the order in which the characters were presented stayed the same.
We included the always attentive and always distracted versions in the study in order to
verify that the subjects could identify the differences in behavior of our virtual characters.
We then included the random and eye-tracked versions of the scene in order to verify our
hypotheses: that a character that changed behavior was more realistic than a character that
did not and that it was even more realistic when these changes were not random but depended
on human actions. Finally, the subjects were asked to evaluate each of the four characters by
answering a set of questions using a five-point Likert scale [Likert, 1932]:
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