Mona Lisa's smile--perception or deception?

What gives Mona Lisa s smile such a mysterious quality? Livingstone (2000) has suggested that the portrait changes its expression depending on where on the portrait the observer looks. The mouth, which is the essential feature of Mona Lisa s remarkable expression (Kontsevich & Tyler, 2004), appears to form an enigmatic smile. Due to sfumato technique (Gombrich, 2005), this impression of a smile is more prominent in the gradual luminance changes that observers perceive mainly in the periphery of their vision— that is, in low spatial-frequency ranges. It is less prominent in the fine details that observers perceive only at the center of their gaze, in high spatial-frequency ranges. Consequently, the subtle smile one perceives while looking at Mona Lisa s eyes (when her mouth appears blurred) vanishes when one attempts to verify this impression by looking at the mouth with maximum visual acuity. Hence, the proposed basis for the elusive quality of Mona Lisa s smile is that ‘‘you can t catch her smile by looking at her mouth. She smiles until you look at her mouth’’ (Livingstone, 2000, p. 1299). In this study, we simulated the phenomenon for the first time experimentally via a saccade-contingent display-change technique that allowed us to subliminally alter the expression of faces depending on the beholder s gaze position.