By definition, sensations are experienced practically instantaneously, based on changes in the current situation. Two factors may cause sensations: the current perceptions (that is, stimuli from the environment), or cognitive activity (that is, thinking). Table 37.1 lists common sensations.
Typically, a sensation is triggered by perceptions. The body detects stimuli from the environment, and the information causes an immediate reaction in the brain. For example, a nonplayer character (NPC) may experience a sensation of surprise when a player appears suddenly.
Embodied creatures are defined by their interaction with the world, so the perceptual type of sensations will be the most common (see Table 37.2). The reactive techniques studied throughout this book are appropriate for creating such reactive emotions.
Sensations may also be triggered by reactions to the mental state (for instance, knowledge of the world or other emotions). Here, basic processing of information in the brain causes the sensation. For instance, surprise can be caused by an object not being present, when the animat thought it should be there.
Sensations based on cognition and perception have common traits: Both are triggered when a pattern is matched in the brain. With perceptions, this pattern is matched instantly based on sensory information. On the other hand, some cognition is necessary before a pattern develops in the brain (by thinking), which eventually engenders a sensation instantly when a pattern is matched.