Dr Alessandro Soranzo - Reader in Psychology

Investigating the uncatchable smile

In 1998, a little known picture was sold for a modest sum in a New York salesroom and in so doing attracted the attention of the art world. Painstaking analysis by the Oxford art historian Martin Kemp and others revealed it to be the work of Leonardo Da Vinci (Kemp & Cotte, 2010,Hodder & Stoughton). Given the considerable interest in La Bella Principessa, it is perhaps surprising now to suggest that it may contain an illusion. The Principessa mouth appears to change shape depending on whether it is viewed in foveal or peripheral vision and this in turn changes the facial expression and ambience, generating an 'uncatchable smile' experience. Experimental data showed that the uncatchable smile experience can be obtained also by approaching the picture from distance and, when a digital version of the picture was used, by either blurring or pixelating the image. The effect is similar, and perhaps stronger, to that described by the Harvard neurobiologist Margaret Livingstone, in her account of the Mona Lisa's enigmatic smile (Livingstone, 2002, Abrahams). The question arises whether Leonardo deliberately used such an artefact as a subtle embellishment to the overall aesthetic - after all, who can resist an uncatchable smile?

In this project, Michael Pickard and Alessandro Soranzo, are investigating the uncatchable smile illusion that can be noticed in La Bella Principessa's portrait.

In particular, we test four hypotheses:

• Hypothesis 1: Distance will influence the viewer's perception of contentment in La Bella Principessa's portrait, specifically that a higher level of contentment will be reported by those viewing the portrait from further away (Far condition) compared to those viewing it up close (Close condition).
• Hypothesis 2:  An increased level of Gaussian blur will increase the viewer's perception of contentment in La Bella Principessa's portrait but not the control portrait.
• Hypothesis 3: The viewer's perception of contentment in La Bella Principessa's portrait is more attributable to her mouth rather than her eyes alone, or her eyes and mouth.
• Hypothesis 4: Gaussian blur will influence the viewer's perception of the mouth slant in La Bella Principessa's portrait but not the control portrait.