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Layers of emotion Fundamental to our AE-based behavior system is the notion that emotions comprise three layers of behavior. At the top level are what we term momentary emotions; these are the behaviors that we display briefly in reaction to events. For example, momentary emotions occur when we smile or laugh at a joke or when we are surprised to see an old friend unexpectedly. At the next level are moods. Moods are prolonged emotional states caused by the cumulative effect of momentary emotions. Underlying both of these layers and always present is our personality; this is the behavior that we generally display when no momentary emotion or mood overrides (Figure 1).
These levels have an order of priority. Momentary emotions have priority over mood when determining which behavior to display. One’s mood, in turn, has priority over one’s personality (Figure 2)
Figures 1 and 2 show the various layers of emotional behavior. Momentary emotions are brief reactions to events that assume the highest priority when we select our behavior. These momentary behaviors are short-lived and decay quickly. Moods are produced by momentary emotions, usually by the cumulative affects of a series of momentary emotions. Moods can gradually increase in prominence even after the momentary emotions have subdued. The development of moods depends on whether the momentary emotions are positive or negative (punishments or rewards in a reinforcement sense). If a character were to receive a stream of negative momentary emotions, then the mood would obviously be bad and would decay slowly. The personality layer is always present and has a consistent level of prominence. The behavior that a character displays depends upon each emotional layer’s prominence. The more prominent the layer, the higher the probability of that behavior being selected. Where can we use AE? With the notable exceptions of P.F. Magic’s Catz and Dogz series, Fujitsu’s fin fin, and Cyberlife’s Creatures series, autonomous AE of any significant depth is rarely seen in the world of interactive entertainment. Why is this the case? The field of interactive entertainment is dominated by genres that require the user to either conquer and/or to kill everything in his or her path. Little emotion is required by the opposition, besides perhaps a little hard-coded fear or aggression that manifests itself in simple movement patterns. Emotion primarily serves a social function in interactive entertainment. Emotional responses are used to make the characters that we encounter believable and engaging. For example, if we were to walk into a virtual bar and all of the characters in the bar had distinct personalities, the scene would be a very immersive and believable social situation. If the characters showed no emotion, our suspension of disbelief would be immediately broken and we would be reminded that we were in a computer-generated simulation rather than in our own fantasy world. Of course, if all of the bar’s customers had guns and our sole purpose was to dispatch them to a simulated afterlife, then this really wouldn’t constitute a social situation and emotion might not be required. A key to the use of AE, then, is the context of situations in which it is used. An important area of growth is in the field of girls’ entertainment, pioneered by Purple Moon and its friendship adventures built on Brenda Laurel’s excellent research into girls’ play behavior and girls and sport. For more information on Ms. Laurel’s research, see http://www.purple-moon.com/cb/laslink/pm?stat+corp+play_behavior and http://www.purple-moon.com/cb/laslink/pm?stat+corp+girl_sport. Social cooperation is a key element in this area and as such is an ideal place to use autonomous characters with AE. In these situations, the characters’ emotional states and their emotional responses to the players’ actions are what make the experience enjoyable, interesting, and entertaining. After playing the first of Purple Moon’s titles, I was a little disappointed to find that it used only static animations, which limited its sense of immersion. A full, living, 3D world would have increased its impact (and cost) dramatically.
Of course, processor overhead is always a problem with an element as computationally complex as AE. The reason that Catz, Dogz, and Creatures succeed in displaying characters with believable emotional behavior is that this element is generally the games’ sole area of concern. Graphics and other elements are kept to an acceptable minimum so that maximum resources can be devoted to behavior generation. As we’re not yet at the stage where we can throw unlimited resources at character AE, we should learn from those titles that employ it successfully and design our simulations intelligently with these constraints in mind. In other words, fight the battles you can win. Still, a significant amount of ingenuity and optimization would certainly contribute to the use and availability of AE. Consider the graphics technique of LOD (level of detail), in which objects farther from the viewer are displayed in progressively lower and lower levels of detail. Using LOE (level of emotion), characters farther away from the viewer would generate and display progressively lower and lower levels of emotion. If a character is out of sight, we generally don’t care about its emotional state. In addition, one can also be careful in the choice of characters to use. Using human characters necessarily implies that their behavior is deep and complex. Unfortunately, because we are most attuned to recognizing human emotion, we are also very well attuned at recognizing flawed human behavior, which can break the illusion of an otherwise well-constructed simulated environment. One way to attack this problem is to use nonhuman characters. Cats, dogs, and Norns all show engaging levels of interactive emotional behavior that maintains the illusion of life without having, or needing, the complexity of human emotional responses. An important point to reiterate here is that we’re specifically dealing with autonomous interactive characters. These characters have responses and behaviors that cannot be prescripted or predefined to any great degree and must instead employ systems that are able to produce behavior in response to changes in the environment and interactions with the user. |
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