Hodne – Omnivoyance / 1 Omnivoyance: The Use of Optical Illusion in the Depiction of the Face of God in Medieval Art by Lasse Hodne Department of Art and Media Studies Norwegian University of Science and Technology (NTNU) lasse.hodne@ntnu.no Abstract: The illusion of omnivoyance (also called the Mona Lisa effect) as an embodiment of mysterious powers is suited for the representation of the Supreme Being in any religion, but its central position in Christian art may be due to the fact that the Christian god is defined as all-seeing. The conscious use of this effect throughout the Middle Ages is testified to not only by the systematic use of the full-face view in representations of divinity but also by the inclusion of inscriptions that emphasise God’s absolute nature in the same way as omnivoyance does. Scientifically speaking, the illusion of omnivoyance, the feeling that the eyes of a person depicted in a painting follow you, is a well-known optical illusion that only works with flat images. In order for the effect to be achieved, the face must be painted or drawn on a flat surface with the eyes directed out of the picture at an angle of 90 degrees with respect to the picture plane (Fig. 1). It may be turned to us en face but not necessarily so. In the psychological literature, the phenomenon is most commonly referred to as ‘the Mona Lisa effect’ named after Leonardo da Vinci’s famous painting in the Louvre in Paris. Cognitive psychologists have dedicated some attention to the omnivoyance effect, trying to find out whether or not the optical illusion also works along the vertical axis as well as the horizontal. 1 Others have 1 Boyarskaya and Hecht, p. 31. experimented to determine to which degree the direction of the eyes and the head’s orientation work together to define the direction of the gaze. 2 Standing on Meyer Schapiro’s brief historical survey from 1973, 3 one of the first who brought attention to the phenomenon was Pliny the Elder (AD 23–AD 79). In his Naturalis Historia, he described a painting by the artist Famulus of the goddess Athena ‘whose eyes are turned to the spectator from whatever side he may be looking.’ 4 In the following century, Lucian (AD 125– AD 180) observed about an image of the goddess Hera in the Temple at Hierapolis: ‘. . . if you stand over against it, it looks you in the face, and as you pass it the gaze still follows you, and if another approaching from a different quarter looks at it, he is similarly affected.’ 5 The first who attempted to give this optical illusion a scientific explanation was Ptolemy (AD 90–AD 168), who, more than a thousand years before the introduction of central perspective, described the phenomenon by means of terms normally associated with Renaissance perspective, like ‘visual cone’ and ‘visual axis.’ 6 2 Todorović, pp. 3549–3562. 3 Schapiro, p. 39, n. 80. See also Barasch, p. 41; Koerner, p. 127. 4 Quoted through Schapiro, p. 39, n. 80; Pliny, Naturalis Historia 35, p. 149. 5 Lucian, p. 73. 6 Emphasising that the omnivoyance effect is limited to images painted on panel and not to sculpture, Ptolemy concluded that: ‘. . . the reason is that the true direction of the painted face’s gaze is perceived by means only of the stationary disposition of the visual cone that strikes the painted face. The visual faculty does not recognize this, but the gaze remains fixed solely along the visual axis. . . . Thus, as the observer moves away, he supposes that the image’s gaze follows him.’ Ptolemy, p. 124.