Realistic eye model for embodied conversational agents

The eyes play an essential role during face to face communication. They provide important information about visual attention and turn-taking during human-human and human-avatar interaction. In fact, the eye is a complex organ and gaze is only one of its behaviours. It is composed, among other components, of an eyeball, an iris, a pupil and a cornea. The pupil and the cornea present time-varying phenomena that a realistic eye model should take into account. The primary role of the pupil is to regulate the amount of light entering the eye in response to the changing environmental illumination. The pupil dilates in low illumination conditions and constricts in high illumination conditions. A physiologically inspired (time varying) model of pupil light reflex was proposed by Pamplona and colleagues [Pamplona et al. 2009]. Another kind of pupillary movements are hippus which correspond to spontaneous oscillations of the pupil diameter under steady conditions of illumination. It is considered as a chaotic system with period doubling [Rosenberg and Kroll 1999]. In fact, the oscillations (with a frequency equal to 0.2 Hz) go from chaotic to periodic behaviours and vice-versa. The eyeball is composed of the sclera and the cornea. The sclera is the tough, fibrous outer layer of the eyeball that forms the whites of the eyes. Another eye component is the cornea which is a transparent tissue that covers the iris. On its surface, a reflection of the world surrounding the person appears: this effect is called corneal reflection. Only recently, an anatomically accurate eye model (replicating video of human eye) has been implemented that takes into account this reflection [François et al. 2007] but not tested embedded in an avatar interacting with humans. The aim of this study was to build a 3D eye model for virtual humans replicating corneal reflection, pupil size variation due to bottom-up processes and the hippus phenomenon.