  This study extends the mathematical model of emotion dimensions that we
previously proposed (Yanagisawa, et al. 2019, Front Comput Neurosci) to
consider perceived complexity as well as novelty, as a source of arousal
potential. Berlyne's hedonic function of arousal potential (or the inverse
U-shaped curve, the so-called Wundt curve) is assumed. We modeled the arousal
potential as information contents to be processed in the brain after sensory
stimuli are perceived (or recognized), which we termed sensory surprisal. We
mathematically demonstrated that sensory surprisal represents free energy, and
it is equivalent to a summation of information gain (or information from
novelty) and perceived complexity (or information from complexity), which are
the collative variables forming the arousal potential. We demonstrated
empirical evidence with visual stimuli (profile shapes of butterfly) supporting
the hypothesis that the summation of perceived novelty and complexity shapes
the inverse U-shaped beauty function. We discussed the potential of free energy
as a mathematical principle explaining emotion initiators.
