“…For example, an ordering system recommends food items to customers from their facial expressions and eye motions [1], and a therapist system infers users' emotions from facial expressions and voices to support their mental states [2]. Previous studies aimed to detect laughter based on facial expressions, voices, and electromyograms related to laughter behaviors, rather than to estimate subjective fun [3]- [6]. In some situations, sensors for measuring these signals are unavailable.…”