Dr Alessandro Soranzo, psychology professor and visual perception expert at Sheffield Hallam University led the research into the comparison between La Bella Principessa and La Gioconda. The former features, Bianca Sforza, the 13-year-old daughter of the duke of Milan, Ludovico Sforza, before she is to be wed to a commander of the Milanese forces.

The research included comparing how viewers perceived both the paintings at different distances and levels of focus, with Piero del Pollaiuolo's Portrait of a Girl used as a control. The researchers discovered that from a greater distance or with a greater blur, both Da Vinci's paintings were perceived as having smiles, whilst Del Pollaiuolo's subject did not. Although Dr Soranzo states that this is not conclusive proof that Da Vinci used the same 'smile' technique for both portraits.