In the following analysis we will limit our consideration of emotion intensity to variables that pertain to what Frijda et al. [Frijda et al. 1992] refer to as the overall felt intensity of an emotion. They describe overall felt intensity as comprising ``whatever would go into the generation of a response to a global question such as this: `How intense was your emotional reaction to situation S?'''
We have segregated variables thought to affect the intensity of emotion into three groups. The first group, simulation-event variables, comprises variables whose values change independently of situation interpretation mechanisms. The second group, stable disposition variables, consists of variables that are involved in an agent's interpretation of situations, tend to be constant, and help to determine an agent's personality and role in the simulation. The last group, mood-relevant variables, contains those variables that contribute to an agent's mood state.
The values in the simulation-event variables group change independently of an agent's interpretation of them. In other words, although these variables are still subject to appraisal by the agent, the value changes themselves are external to the appraising agents. Another way to consider these variables is that a single change in the value of one of them may simultaneously, and differentially, affect several appraising agents. Such variables capture ``objective'' features of the world such as the loudness of a noise or the brightness of a light. Thus, for example, the objective degree of loudness of a piece of music might relate to its appealingness for one agent, but to its repulsiveness for another.
Nonetheless, the volume of the music, a variable within the emotion-eliciting situation, in both cases contributes to the calculation of the intensity for the resulting emotions.
By contrast, the stable disposition variables group contains variables that help to determine an agent's bias toward interpreting an emotion-eliciting situation one way or another. For example, it would be these which would allow us to specify that, for a given volume level, one agent experiences intense dislike for the music, whereas another experiences only mild dislike. That these variables are considered stable does not mean that they can never change but rather that such changes are rather slow, and tend to be unidirectional. For example, someone who finds rap music repulsive, may, over time, come to dislike it less, or even, ultimately, to find it appealing. This group also includes some relationship variables that help to define the strength of friendship or animosity between agents, and their emotional distance.
The last group, the mood-relevant variables, contains variables which (1) alter an agent's interpretation of situations, (2) are volatile, (3) are bipolar in nature, (4) are not dispositional, so that they naturally return to (agent-specific) default values over time, and (5) may be the result of prior affective experience. For example, if an agent is represented as ``feeling unwell or depressed,'' then hearing rap music might be simulated as being particularly uplifting, ``taking the agent's mind off her pain,'' or as particularly intolerable, ``driving her to distraction.''
Our current simulation work is based on the proposals of Ortony, et
al. [Ortony et al.
1988], and Frijda et al. [Frijda et al.
1992], and most of our
intensity variables derive in one form or anther from their work.
The main question that arises in
trying to implement these and other variables in a computer program that
generates simulated emotions is, what features are present (or might be
present) in the simulation events, and how can they be represented in ways
that lead to human-like emotions on the parts of our automated agents?
The three central variables described by Ortony, et al. [Ortony et al. 1988] (i.e., the desirability of an event, the blameworthiness or praiseworthiness of an act, or the attractiveness of an object, or agent construed as an object) determine the valence of the resulting emotion. In addition, these variables, each given here as a simulation event variable / stable disposition variable pair representing the actual feature values within the simulation, and their importance to the agent, are also the primary determinants of emotional intensity. Secondary to these are variables, such as that representing physiological arousal, which modify the base intensity levels generated by the central variables. Some variables only admit values that can reduce or maintain the intensity of an emotion. For example, events are ordinarily assumed to be perceived as real. However, if explicitly represented otherwise, the intensity of an emotion resulting from the (at least partially perceived as unreal) situation will be lessened. Lastly, some variables are represented as pairs containing a bias factor and a strength, and will act differently on the intensities of differently valenced emotions.